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Vitamin A - Wikipedia
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class="vector-toc-list"> </ul> </li> <li id="toc-Activation_and_excretion" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Activation_and_excretion"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Activation and excretion</span> </div> </a> <ul id="toc-Activation_and_excretion-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Metabolic_functions" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Metabolic_functions"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Metabolic functions</span> </div> </a> <button aria-controls="toc-Metabolic_functions-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Metabolic functions subsection</span> </button> <ul id="toc-Metabolic_functions-sublist" class="vector-toc-list"> <li id="toc-Vision_and_eye_health" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Vision_and_eye_health"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Vision and eye health</span> </div> </a> <ul id="toc-Vision_and_eye_health-sublist" class="vector-toc-list"> <li id="toc-Vision" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Vision"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1.1</span> <span>Vision</span> </div> </a> <ul id="toc-Vision-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Night_blindness" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Night_blindness"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1.2</span> <span>Night blindness</span> </div> </a> <ul id="toc-Night_blindness-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Xerophthalmia_and_childhood_blindness" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Xerophthalmia_and_childhood_blindness"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1.3</span> <span>Xerophthalmia and childhood blindness</span> </div> </a> <ul id="toc-Xerophthalmia_and_childhood_blindness-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Gene_regulation" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Gene_regulation"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Gene regulation</span> </div> </a> <ul id="toc-Gene_regulation-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Embryology" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Embryology"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Embryology</span> </div> </a> <ul id="toc-Embryology-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Immune_functions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Immune_functions"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Immune functions</span> </div> </a> <ul id="toc-Immune_functions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Skin" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Skin"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.5</span> <span>Skin</span> </div> </a> <ul id="toc-Skin-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Units_of_measurement" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Units_of_measurement"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Units of measurement</span> </div> </a> <ul id="toc-Units_of_measurement-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Dietary_recommendations" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Dietary_recommendations"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Dietary recommendations</span> </div> </a> <button aria-controls="toc-Dietary_recommendations-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Dietary recommendations subsection</span> </button> <ul id="toc-Dietary_recommendations-sublist" class="vector-toc-list"> <li id="toc-Safety" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Safety"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1</span> <span>Safety</span> </div> </a> <ul id="toc-Safety-sublist" class="vector-toc-list"> <li id="toc-Retinol_safety" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Retinol_safety"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1.1</span> <span>Retinol safety</span> </div> </a> <ul id="toc-Retinol_safety-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-β-carotene_safety" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#β-carotene_safety"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1.2</span> <span>β-carotene safety</span> </div> </a> <ul id="toc-β-carotene_safety-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Carotenosis" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Carotenosis"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1.3</span> <span>Carotenosis</span> </div> </a> <ul id="toc-Carotenosis-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-U.S._labeling" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#U.S._labeling"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.2</span> <span>U.S. labeling</span> </div> </a> <ul id="toc-U.S._labeling-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Sources" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Sources"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Sources</span> </div> </a> <button aria-controls="toc-Sources-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Sources subsection</span> </button> <ul id="toc-Sources-sublist" class="vector-toc-list"> <li id="toc-Fortification" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fortification"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Fortification</span> </div> </a> <ul id="toc-Fortification-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Vitamin_A_supplementation_(VAS)" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Vitamin_A_supplementation_(VAS)"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>Vitamin A supplementation (VAS)</span> </div> </a> <ul id="toc-Vitamin_A_supplementation_(VAS)-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Deficiency" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Deficiency"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Deficiency</span> </div> </a> <button aria-controls="toc-Deficiency-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Deficiency subsection</span> </button> <ul id="toc-Deficiency-sublist" class="vector-toc-list"> <li id="toc-Primary_causes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Primary_causes"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.1</span> <span>Primary causes</span> </div> </a> <ul id="toc-Primary_causes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Secondary_causes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Secondary_causes"> <div class="vector-toc-text"> <span class="vector-toc-numb">7.2</span> <span>Secondary causes</span> </div> </a> <ul id="toc-Secondary_causes-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Animal_requirements" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Animal_requirements"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Animal requirements</span> </div> </a> <ul id="toc-Animal_requirements-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Medical_uses" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Medical_uses"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Medical uses</span> </div> </a> <button aria-controls="toc-Medical_uses-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Medical uses subsection</span> </button> <ul id="toc-Medical_uses-sublist" class="vector-toc-list"> <li id="toc-Preventing_and_treating_vitamin_A_deficiency" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Preventing_and_treating_vitamin_A_deficiency"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.1</span> <span>Preventing and treating vitamin A deficiency</span> </div> </a> <ul id="toc-Preventing_and_treating_vitamin_A_deficiency-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Acne" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Acne"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.2</span> <span>Acne</span> </div> </a> <ul id="toc-Acne-sublist" class="vector-toc-list"> <li id="toc-Topical_retinoic_acid_and_retinol" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Topical_retinoic_acid_and_retinol"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.2.1</span> <span>Topical retinoic acid and retinol</span> </div> </a> <ul id="toc-Topical_retinoic_acid_and_retinol-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Oral_isotretinoin" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Oral_isotretinoin"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.2.2</span> <span>Oral isotretinoin</span> </div> </a> <ul id="toc-Oral_isotretinoin-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Other_dermatological_conditions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Other_dermatological_conditions"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.3</span> <span>Other dermatological conditions</span> </div> </a> <ul id="toc-Other_dermatological_conditions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Immune_function" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Immune_function"> <div class="vector-toc-text"> <span class="vector-toc-numb">9.4</span> <span>Immune function</span> </div> </a> <ul id="toc-Immune_function-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Synthesis" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Synthesis"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>Synthesis</span> </div> </a> <button aria-controls="toc-Synthesis-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Synthesis subsection</span> </button> <ul id="toc-Synthesis-sublist" class="vector-toc-list"> <li id="toc-Biosynthesis" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Biosynthesis"> <div class="vector-toc-text"> <span class="vector-toc-numb">10.1</span> <span>Biosynthesis</span> </div> </a> <ul id="toc-Biosynthesis-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Industrial_synthesis" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Industrial_synthesis"> <div class="vector-toc-text"> <span class="vector-toc-numb">10.2</span> <span>Industrial synthesis</span> </div> </a> <ul id="toc-Industrial_synthesis-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Research" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Research"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>Research</span> </div> </a> <button aria-controls="toc-Research-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Research subsection</span> </button> <ul id="toc-Research-sublist" class="vector-toc-list"> <li id="toc-Brain" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Brain"> <div class="vector-toc-text"> <span class="vector-toc-numb">11.1</span> <span>Brain</span> </div> </a> <ul id="toc-Brain-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Cancer" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cancer"> <div class="vector-toc-text"> <span class="vector-toc-numb">11.2</span> <span>Cancer</span> </div> </a> <ul id="toc-Cancer-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Fetal_alcohol_spectrum_disorder" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fetal_alcohol_spectrum_disorder"> <div class="vector-toc-text"> <span class="vector-toc-numb">11.3</span> <span>Fetal alcohol spectrum disorder</span> </div> </a> <ul id="toc-Fetal_alcohol_spectrum_disorder-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Malaria" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Malaria"> <div class="vector-toc-text"> <span class="vector-toc-numb">11.4</span> <span>Malaria</span> </div> </a> <ul id="toc-Malaria-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-In_history" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#In_history"> <div class="vector-toc-text"> <span class="vector-toc-numb">12</span> <span>In history</span> </div> </a> <ul id="toc-In_history-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">13</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">14</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Vitamin A</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 86 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-86" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">86 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Vitamien_A" title="Vitamien A – Afrikaans" lang="af" hreflang="af" data-title="Vitamien A" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%81%D9%8A%D8%AA%D8%A7%D9%85%D9%8A%D9%86_%D8%A3%D9%84%D9%81" title="فيتامين ألف – Arabic" lang="ar" hreflang="ar" data-title="فيتامين ألف" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Asturian" lang="ast" hreflang="ast" data-title="Vitamina A" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/A_vitamini" title="A vitamini – Azerbaijani" lang="az" hreflang="az" data-title="A vitamini" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-azb mw-list-item"><a href="https://azb.wikipedia.org/wiki/%D9%88%DB%8C%D8%AA%D8%A7%D9%85%DB%8C%D9%86_%D8%A2" title="ویتامین آ – South Azerbaijani" lang="azb" hreflang="azb" data-title="ویتامین آ" data-language-autonym="تۆرکجه" data-language-local-name="South Azerbaijani" class="interlanguage-link-target"><span>تۆرکجه</span></a></li><li class="interlanguage-link interwiki-ban mw-list-item"><a href="https://ban.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Balinese" lang="ban" hreflang="ban" data-title="Vitamin A" data-language-autonym="Basa Bali" data-language-local-name="Balinese" class="interlanguage-link-target"><span>Basa Bali</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%AD%E0%A6%BF%E0%A6%9F%E0%A6%BE%E0%A6%AE%E0%A6%BF%E0%A6%A8_%E0%A6%8F" title="ভিটামিন এ – Bangla" lang="bn" hreflang="bn" data-title="ভিটামিন এ" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-bcl mw-list-item"><a href="https://bcl.wikipedia.org/wiki/Bitamina_A" title="Bitamina A – Central Bikol" lang="bcl" hreflang="bcl" data-title="Bitamina A" data-language-autonym="Bikol Central" data-language-local-name="Central Bikol" class="interlanguage-link-target"><span>Bikol Central</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_%D0%90" title="Витамин А – Bulgarian" lang="bg" hreflang="bg" data-title="Витамин А" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Bosnian" lang="bs" hreflang="bs" data-title="Vitamin A" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Catalan" lang="ca" hreflang="ca" data-title="Vitamina A" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Vitam%C3%ADn_A" title="Vitamín A – Czech" lang="cs" hreflang="cs" data-title="Vitamín A" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/Fitamin_A" title="Fitamin A – Welsh" lang="cy" hreflang="cy" data-title="Fitamin A" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target"><span>Cymraeg</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Danish" lang="da" hreflang="da" data-title="Vitamin A" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – German" lang="de" hreflang="de" data-title="Vitamin A" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-dv mw-list-item"><a href="https://dv.wikipedia.org/wiki/%DE%88%DE%A8%DE%93%DE%A6%DE%89%DE%A8%DE%82%DE%B0_%DE%87%DE%AD" title="ވިޓަމިން އޭ – Divehi" lang="dv" hreflang="dv" data-title="ވިޓަމިން އޭ" data-language-autonym="ދިވެހިބަސް" data-language-local-name="Divehi" class="interlanguage-link-target"><span>ދިވެހިބަސް</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/A-vitamiin" title="A-vitamiin – Estonian" lang="et" hreflang="et" data-title="A-vitamiin" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%92%CE%B9%CF%84%CE%B1%CE%BC%CE%AF%CE%BD%CE%B7_%CE%91" title="Βιταμίνη Α – Greek" lang="el" hreflang="el" data-title="Βιταμίνη Α" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Spanish" lang="es" hreflang="es" data-title="Vitamina A" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Vitamino_A" title="Vitamino A – Esperanto" lang="eo" hreflang="eo" data-title="Vitamino A" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/A_bitamina" title="A bitamina – Basque" lang="eu" hreflang="eu" data-title="A bitamina" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%88%DB%8C%D8%AA%D8%A7%D9%85%DB%8C%D9%86_%D8%A2" title="ویتامین آ – Persian" lang="fa" hreflang="fa" data-title="ویتامین آ" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fo mw-list-item"><a href="https://fo.wikipedia.org/wiki/A_vitamin" title="A vitamin – Faroese" lang="fo" hreflang="fo" data-title="A vitamin" data-language-autonym="Føroyskt" data-language-local-name="Faroese" class="interlanguage-link-target"><span>Føroyskt</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Vitamine_A" title="Vitamine A – French" lang="fr" hreflang="fr" data-title="Vitamine A" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Galician" lang="gl" hreflang="gl" data-title="Vitamina A" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EB%B9%84%ED%83%80%EB%AF%BC_A" title="비타민 A – Korean" lang="ko" hreflang="ko" data-title="비타민 A" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%8E%D5%AB%D5%BF%D5%A1%D5%B4%D5%AB%D5%B6_A" title="Վիտամին A – Armenian" lang="hy" hreflang="hy" data-title="Վիտամին A" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%B5%E0%A4%BF%E0%A4%9F%E0%A4%BE%E0%A4%AE%E0%A4%BF%E0%A4%A8_%E0%A4%8F" title="विटामिन ए – Hindi" lang="hi" hreflang="hi" data-title="विटामिन ए" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr badge-Q17437796 badge-featuredarticle mw-list-item" title="featured article badge"><a href="https://hr.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Croatian" lang="hr" hreflang="hr" data-title="Vitamin A" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Indonesian" lang="id" hreflang="id" data-title="Vitamin A" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/A-v%C3%ADtam%C3%ADn" title="A-vítamín – Icelandic" lang="is" hreflang="is" data-title="A-vítamín" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%95%D7%99%D7%98%D7%9E%D7%99%D7%9F_A" title="ויטמין A – Hebrew" lang="he" hreflang="he" data-title="ויטמין A" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-jv mw-list-item"><a href="https://jv.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Javanese" lang="jv" hreflang="jv" data-title="Vitamin A" data-language-autonym="Jawa" data-language-local-name="Javanese" class="interlanguage-link-target"><span>Jawa</span></a></li><li class="interlanguage-link interwiki-kn mw-list-item"><a href="https://kn.wikipedia.org/wiki/%E0%B2%8E_%E0%B2%9C%E0%B3%80%E0%B2%B5%E0%B2%B8%E0%B2%A4%E0%B3%8D%E0%B2%B5" title="ಎ ಜೀವಸತ್ವ – Kannada" lang="kn" hreflang="kn" data-title="ಎ ಜೀವಸತ್ವ" data-language-autonym="ಕನ್ನಡ" data-language-local-name="Kannada" class="interlanguage-link-target"><span>ಕನ್ನಡ</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%95%E1%83%98%E1%83%A2%E1%83%90%E1%83%9B%E1%83%98%E1%83%9C%E1%83%98_A" title="ვიტამინი A – Georgian" lang="ka" hreflang="ka" data-title="ვიტამინი A" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-rw mw-list-item"><a href="https://rw.wikipedia.org/wiki/Vitamini_A" title="Vitamini A – Kinyarwanda" lang="rw" hreflang="rw" data-title="Vitamini A" data-language-autonym="Ikinyarwanda" data-language-local-name="Kinyarwanda" class="interlanguage-link-target"><span>Ikinyarwanda</span></a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Vitamini_A" title="Vitamini A – Swahili" lang="sw" hreflang="sw" data-title="Vitamini A" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target"><span>Kiswahili</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Vitaminum_A" title="Vitaminum A – Latin" lang="la" hreflang="la" data-title="Vitaminum A" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/A_vitam%C4%ABns" title="A vitamīns – Latvian" lang="lv" hreflang="lv" data-title="A vitamīns" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Vitaminas_A" title="Vitaminas A – Lithuanian" lang="lt" hreflang="lt" data-title="Vitaminas A" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-lfn mw-list-item"><a href="https://lfn.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Lingua Franca Nova" lang="lfn" hreflang="lfn" data-title="Vitamina A" data-language-autonym="Lingua Franca Nova" data-language-local-name="Lingua Franca Nova" class="interlanguage-link-target"><span>Lingua Franca Nova</span></a></li><li class="interlanguage-link interwiki-jbo mw-list-item"><a href="https://jbo.wikipedia.org/wiki/abumoi_mivytcuxu%27i" title="abumoi mivytcuxu'i – Lojban" lang="jbo" hreflang="jbo" data-title="abumoi mivytcuxu'i" data-language-autonym="La .lojban." data-language-local-name="Lojban" class="interlanguage-link-target"><span>La .lojban.</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/A-vitamin" title="A-vitamin – Hungarian" lang="hu" hreflang="hu" data-title="A-vitamin" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_%D0%90" title="Витамин А – Macedonian" lang="mk" hreflang="mk" data-title="Витамин А" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%9C%E0%B5%80%E0%B4%B5%E0%B4%95%E0%B4%82_%E0%B4%8E" title="ജീവകം എ – Malayalam" lang="ml" hreflang="ml" data-title="ജീവകം എ" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-mr mw-list-item"><a href="https://mr.wikipedia.org/wiki/%E0%A4%85-%E0%A4%9C%E0%A5%80%E0%A4%B5%E0%A4%A8%E0%A4%B8%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A5%8D%E0%A4%B5" title="अ-जीवनसत्त्व – Marathi" lang="mr" hreflang="mr" data-title="अ-जीवनसत्त्व" data-language-autonym="मराठी" data-language-local-name="Marathi" class="interlanguage-link-target"><span>मराठी</span></a></li><li class="interlanguage-link interwiki-xmf mw-list-item"><a href="https://xmf.wikipedia.org/wiki/%E1%83%95%E1%83%98%E1%83%A2%E1%83%90%E1%83%9B%E1%83%98%E1%83%9C%E1%83%98_A" title="ვიტამინი A – Mingrelian" lang="xmf" hreflang="xmf" data-title="ვიტამინი A" data-language-autonym="მარგალური" data-language-local-name="Mingrelian" class="interlanguage-link-target"><span>მარგალური</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Malay" lang="ms" hreflang="ms" data-title="Vitamin A" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_%D0%90" title="Витамин А – Mongolian" lang="mn" hreflang="mn" data-title="Витамин А" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-nl badge-Q70894304 mw-list-item" title=""><a href="https://nl.wikipedia.org/wiki/Vitamine_A" title="Vitamine A – Dutch" lang="nl" hreflang="nl" data-title="Vitamine A" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ne mw-list-item"><a href="https://ne.wikipedia.org/wiki/%E0%A4%AD%E0%A4%BF%E0%A4%9F%E0%A4%BE%E0%A4%AE%E0%A4%BF%E0%A4%A8_%E0%A4%8F" title="भिटामिन ए – Nepali" lang="ne" hreflang="ne" data-title="भिटामिन ए" data-language-autonym="नेपाली" data-language-local-name="Nepali" class="interlanguage-link-target"><span>नेपाली</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%83%93%E3%82%BF%E3%83%9F%E3%83%B3A" title="ビタミンA – Japanese" lang="ja" hreflang="ja" data-title="ビタミンA" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Vitamin A" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-oc mw-list-item"><a href="https://oc.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Occitan" lang="oc" hreflang="oc" data-title="Vitamina A" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target"><span>Occitan</span></a></li><li class="interlanguage-link interwiki-or mw-list-item"><a href="https://or.wikipedia.org/wiki/%E0%AC%9C%E0%AD%80%E0%AC%AC%E0%AC%B8%E0%AC%BE%E0%AC%B0_%E0%AC%95" title="ଜୀବସାର କ – Odia" lang="or" hreflang="or" data-title="ଜୀବସାର କ" data-language-autonym="ଓଡ଼ିଆ" data-language-local-name="Odia" class="interlanguage-link-target"><span>ଓଡ଼ିଆ</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%B5%E0%A8%BF%E0%A8%9F%E0%A8%BE%E0%A8%AE%E0%A8%BF%E0%A8%A8_%E0%A8%8F" title="ਵਿਟਾਮਿਨ ਏ – Punjabi" lang="pa" hreflang="pa" data-title="ਵਿਟਾਮਿਨ ਏ" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-ps mw-list-item"><a href="https://ps.wikipedia.org/wiki/%D9%88%D9%8A%D9%BC%D8%A7%D9%85%D9%8A%D9%86_%D8%A7%DB%90" title="ويټامين اې – Pashto" lang="ps" hreflang="ps" data-title="ويټامين اې" data-language-autonym="پښتو" data-language-local-name="Pashto" class="interlanguage-link-target"><span>پښتو</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Witamina_A" title="Witamina A – Polish" lang="pl" hreflang="pl" data-title="Witamina A" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Portuguese" lang="pt" hreflang="pt" data-title="Vitamina A" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Romanian" lang="ro" hreflang="ro" data-title="Vitamina A" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru badge-Q17437798 badge-goodarticle mw-list-item" title="good article badge"><a href="https://ru.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_A" title="Витамин A – Russian" lang="ru" hreflang="ru" data-title="Витамин A" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Albanian" lang="sq" hreflang="sq" data-title="Vitamina A" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-scn mw-list-item"><a href="https://scn.wikipedia.org/wiki/Vitamina_A" title="Vitamina A – Sicilian" lang="scn" hreflang="scn" data-title="Vitamina A" data-language-autonym="Sicilianu" data-language-local-name="Sicilian" class="interlanguage-link-target"><span>Sicilianu</span></a></li><li class="interlanguage-link interwiki-si mw-list-item"><a href="https://si.wikipedia.org/wiki/%E0%B7%80%E0%B7%92%E0%B6%A7%E0%B6%B8%E0%B7%92%E0%B6%B1%E0%B7%8A_A" title="විටමින් A – Sinhala" lang="si" hreflang="si" data-title="විටමින් A" data-language-autonym="සිංහල" data-language-local-name="Sinhala" class="interlanguage-link-target"><span>සිංහල</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Simple English" lang="en-simple" hreflang="en-simple" data-title="Vitamin A" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sd mw-list-item"><a href="https://sd.wikipedia.org/wiki/%D9%88%D9%BD%D8%A7%D9%85%D9%86_%D8%A7%D9%8A" title="وٽامن اي – Sindhi" lang="sd" hreflang="sd" data-title="وٽامن اي" data-language-autonym="سنڌي" data-language-local-name="Sindhi" class="interlanguage-link-target"><span>سنڌي</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Slovenian" lang="sl" hreflang="sl" data-title="Vitamin A" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-ckb mw-list-item"><a href="https://ckb.wikipedia.org/wiki/%DA%A4%DB%8C%D8%AA%D8%A7%D9%85%DB%8C%D9%86_%D8%A6%DB%95%DB%8C" title="ڤیتامین ئەی – Central Kurdish" lang="ckb" hreflang="ckb" data-title="ڤیتامین ئەی" data-language-autonym="کوردی" data-language-local-name="Central Kurdish" class="interlanguage-link-target"><span>کوردی</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_%D0%90" title="Витамин А – Serbian" lang="sr" hreflang="sr" data-title="Витамин А" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Vitamin A" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/A-vitamiini" title="A-vitamiini – Finnish" lang="fi" hreflang="fi" data-title="A-vitamiini" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%89%E0%AE%AF%E0%AE%BF%E0%AE%B0%E0%AF%8D%E0%AE%9A%E0%AF%8D%E0%AE%9A%E0%AE%A4%E0%AF%8D%E0%AE%A4%E0%AF%81_%E0%AE%8F" title="உயிர்ச்சத்து ஏ – Tamil" lang="ta" hreflang="ta" data-title="உயிர்ச்சத்து ஏ" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/A_%D0%B2%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD%D1%8B" title="A витамины – Tatar" lang="tt" hreflang="tt" data-title="A витамины" data-language-autonym="Татарча / tatarça" data-language-local-name="Tatar" class="interlanguage-link-target"><span>Татарча / tatarça</span></a></li><li class="interlanguage-link interwiki-te mw-list-item"><a href="https://te.wikipedia.org/wiki/%E0%B0%B5%E0%B0%BF%E0%B0%9F%E0%B0%AE%E0%B0%BF%E0%B0%A8%E0%B1%8D_%E0%B0%8E" title="విటమిన్ ఎ – Telugu" lang="te" hreflang="te" data-title="విటమిన్ ఎ" data-language-autonym="తెలుగు" data-language-local-name="Telugu" class="interlanguage-link-target"><span>తెలుగు</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%A7%E0%B8%B4%E0%B8%95%E0%B8%B2%E0%B8%A1%E0%B8%B4%E0%B8%99%E0%B9%80%E0%B8%AD" title="วิตามินเอ – Thai" lang="th" hreflang="th" data-title="วิตามินเอ" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/A_vitamini" title="A vitamini – Turkish" lang="tr" hreflang="tr" data-title="A vitamini" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-tyv mw-list-item"><a href="https://tyv.wikipedia.org/wiki/%D0%92%D0%B8%D1%82%D0%B0%D0%BC%D0%B8%D0%BD_A" title="Витамин A – Tuvinian" lang="tyv" hreflang="tyv" data-title="Витамин A" data-language-autonym="Тыва дыл" data-language-local-name="Tuvinian" class="interlanguage-link-target"><span>Тыва дыл</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%92%D1%96%D1%82%D0%B0%D0%BC%D1%96%D0%BD_A" title="Вітамін A – Ukrainian" lang="uk" hreflang="uk" data-title="Вітамін A" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D8%AD%DB%8C%D8%A7%D8%AA%DB%8C%D9%86_%D8%A7%D9%84%D9%81" title="حیاتین الف – Urdu" lang="ur" hreflang="ur" data-title="حیاتین الف" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-ug mw-list-item"><a href="https://ug.wikipedia.org/wiki/%DB%8B%D9%89%D8%AA%D8%A7%D9%85%D9%89%D9%86_A" title="ۋىتامىن A – Uyghur" lang="ug" hreflang="ug" data-title="ۋىتامىن A" data-language-autonym="ئۇيغۇرچە / Uyghurche" data-language-local-name="Uyghur" class="interlanguage-link-target"><span>ئۇيغۇرچە / Uyghurche</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Vitamin_A" title="Vitamin A – Vietnamese" lang="vi" hreflang="vi" data-title="Vitamin A" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-wa mw-list-item"><a href="https://wa.wikipedia.org/wiki/Vitamene_A" title="Vitamene A – Walloon" lang="wa" hreflang="wa" data-title="Vitamene A" data-language-autonym="Walon" data-language-local-name="Walloon" class="interlanguage-link-target"><span>Walon</span></a></li><li class="interlanguage-link interwiki-war mw-list-item"><a href="https://war.wikipedia.org/wiki/Bitamina_A" title="Bitamina A – Waray" lang="war" hreflang="war" data-title="Bitamina A" data-language-autonym="Winaray" data-language-local-name="Waray" class="interlanguage-link-target"><span>Winaray</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/%E7%BB%B4%E7%94%9F%E7%B4%A0A" title="维生素A – Wu" lang="wuu" hreflang="wuu" data-title="维生素A" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E7%B6%AD%E4%BB%96%E5%91%BDA" title="維他命A – Cantonese" lang="yue" hreflang="yue" data-title="維他命A" 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<div class="vector-body-before-content"> <div class="mw-indicators"> <div id="mw-indicator-good-star" class="mw-indicator"><div class="mw-parser-output"><span typeof="mw:File"><a href="/wiki/Wikipedia:Good_articles*" title="This is a good article. Click here for more information."><img alt="This is a good article. Click here for more information." src="//upload.wikimedia.org/wikipedia/en/thumb/9/94/Symbol_support_vote.svg/19px-Symbol_support_vote.svg.png" decoding="async" width="19" height="20" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/94/Symbol_support_vote.svg/29px-Symbol_support_vote.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/94/Symbol_support_vote.svg/39px-Symbol_support_vote.svg.png 2x" data-file-width="180" data-file-height="185" /></a></span></div></div> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Essential nutrient</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">This article is about the family of <a href="/wiki/Vitamer" title="Vitamer">vitamers</a>. For the form usually used as a supplement, see <a href="/wiki/Retinol" title="Retinol">Retinol</a>.</div> <p class="mw-empty-elt"> </p> <div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Pharmaceutical compound</div> <style data-mw-deduplicate="TemplateStyles:r1269284339">@media screen{html.skin-theme-clientpref-night .mw-parser-output .dark_mode_safe img{background-color:var(--background-color-inverted,#f8f9fa)}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .dark_mode_safe img{background-color:var(--background-color-inverted,#f8f9fa)}}</style> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox" style="border-spacing:2px;"><caption class="infobox-title"><span title="International nonproprietary name (INN): Vitamin A">Vitamin A</span></caption><tbody><tr><td colspan="2" class="infobox-image"><span class="mw-default-size skin-invert-image" typeof="mw:File/Frameless"><a href="/wiki/File:All-trans-Retinol2.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/All-trans-Retinol2.svg/220px-All-trans-Retinol2.svg.png" decoding="async" width="220" height="68" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/All-trans-Retinol2.svg/330px-All-trans-Retinol2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5c/All-trans-Retinol2.svg/440px-All-trans-Retinol2.svg.png 2x" data-file-width="457" data-file-height="141" /></a></span></td></tr><tr><td colspan="2" class="infobox-image"><span class="mw-default-size dark_mode_safe" typeof="mw:File/Frameless"><a href="/wiki/File:Retinol_3D_balls.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Retinol_3D_balls.png/220px-Retinol_3D_balls.png" decoding="async" width="220" height="105" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Retinol_3D_balls.png/330px-Retinol_3D_balls.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Retinol_3D_balls.png/440px-Retinol_3D_balls.png 2x" data-file-width="2094" data-file-height="1000" /></a></span><div class="infobox-caption">Retinol (depicted) and retinal play a biological role in vision, but most of the effects of vitamin A are exerted by retinoic acid, which binds to nuclear receptors and regulates gene transcription.</div></td></tr><tr><th colspan="2" class="infobox-header" style="background:#ddd;color:inherit;">Clinical data</th></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/American_Society_of_Health-System_Pharmacists" title="American Society of Health-System Pharmacists">AHFS</a>/<a href="/wiki/Drugs.com" title="Drugs.com">Drugs.com</a></th><td class="infobox-data"><span title="www.drugs.com"><a rel="nofollow" class="external text" href="https://www.drugs.com/monograph/vitamin-a.html">Monograph</a></span></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Regulation_of_therapeutic_goods" title="Regulation of therapeutic goods">License data</a></th><td class="infobox-data"><style data-mw-deduplicate="TemplateStyles:r1126788409">.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style><div class="plainlist"> <ul><li><small><abbr class="country-name" title="United States">US</abbr></small> <a href="/wiki/DailyMed" title="DailyMed">DailyMed</a>: <span title="dailymed.nlm.nih.gov"><a rel="nofollow" class="external text" href="https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=Retinol">Retinol</a></span></li></ul></div> </td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Route_of_administration" title="Route of administration">Routes of<br />administration</a></th><td class="infobox-data"><a href="/wiki/By_mouth" class="mw-redirect" title="By mouth">By mouth</a>, <a href="/wiki/Intramuscular_injection" title="Intramuscular injection">intramuscular</a><sup id="cite_ref-AHFS2016_1-0" class="reference"><a href="#cite_note-AHFS2016-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Drug_class" title="Drug class">Drug class</a></th><td class="infobox-data"><a href="/wiki/Vitamin" title="Vitamin">Vitamin</a></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Anatomical_Therapeutic_Chemical_Classification_System" title="Anatomical Therapeutic Chemical Classification System">ATC code</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><a href="/wiki/ATC_code_A11" title="ATC code A11">A11CA01</a> (<span title="www.whocc.no"><a rel="nofollow" class="external text" href="https://www.whocc.no/atc_ddd_index/?code=A11CA01">WHO</a></span>) <a href="/wiki/ATC_code_D10" title="ATC code D10">D10AD02</a> (<span title="www.whocc.no"><a rel="nofollow" class="external text" href="https://www.whocc.no/atc_ddd_index/?code=D10AD02">WHO</a></span>), <a href="/wiki/ATC_code_R01" title="ATC code R01">R01AX02</a> (<span title="www.whocc.no"><a rel="nofollow" class="external text" href="https://www.whocc.no/atc_ddd_index/?code=R01AX02">WHO</a></span>), <a href="/wiki/ATC_code_S01" title="ATC code S01">S01XA02</a> (<span title="www.whocc.no"><a rel="nofollow" class="external text" href="https://www.whocc.no/atc_ddd_index/?code=S01XA02">WHO</a></span>)</li></ul></div></td></tr><tr><th colspan="2" class="infobox-header" style="background:#ddd;color:inherit;">Legal status</th></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Regulation_of_therapeutic_goods" title="Regulation of therapeutic goods">Legal status</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"> <ul><li><small><abbr class="country-name" title="United States">US</abbr>:</small> <a href="/wiki/Over-the-counter_drug" title="Over-the-counter drug">OTC</a> / Rx-only<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup></li></ul></div> </td></tr><tr><th colspan="2" class="infobox-header" style="background:#ddd;color:inherit;">Identifiers</th></tr><tr><td colspan="2" class="infobox-full-data"><div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold;"><div><a href="/wiki/IUPAC_nomenclature_of_chemistry" title="IUPAC nomenclature of chemistry">IUPAC name</a></div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit; list-style: none; margin-left: 0; word-break:break-all; text-align:left; padding-left:1.5em; text-indent:-1.5em;"><li style="line-height: inherit; margin: 0"><div style="font-size: 97%;">(2<i>E</i>,4<i>E</i>,6<i>E</i>,8<i>E</i>)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraen-1-ol</div></li></ul> </div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/CAS_Registry_Number" title="CAS Registry Number">CAS Number</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="commonchemistry.cas.org"><a rel="nofollow" class="external text" href="https://commonchemistry.cas.org/detail?cas_rn=68-26-8">68-26-8</a></span></li><li>mixture: <span title="commonchemistry.cas.org"><a rel="nofollow" class="external text" href="https://commonchemistry.cas.org/detail?cas_rn=11103-57-4">11103-57-4</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/PubChem#CID" title="PubChem">PubChem</a> <span style="font-weight:normal"><abbr title="Compound ID">CID</abbr></span></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="pubchem.ncbi.nlm.nih.gov"><a rel="nofollow" class="external text" href="https://pubchem.ncbi.nlm.nih.gov/compound/1071">1071</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Guide_to_Pharmacology" title="Guide to Pharmacology">IUPHAR/BPS</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="www.guidetopharmacology.org"><a rel="nofollow" class="external text" href="https://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=4053">4053</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/ChemSpider" title="ChemSpider">ChemSpider</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="www.chemspider.com"><a rel="nofollow" class="external text" href="https://www.chemspider.com/Chemical-Structure.393012.html">393012</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Unique_Ingredient_Identifier" title="Unique Ingredient Identifier">UNII</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="precision.fda.gov"><a rel="nofollow" class="external text" href="https://precision.fda.gov/uniisearch/srs/unii/G2SH0XKK91">G2SH0XKK91</a></span></li><li>mixture: <span title="precision.fda.gov"><a rel="nofollow" class="external text" href="https://precision.fda.gov/uniisearch/srs/unii/81G40H8B0T">81G40H8B0T</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/ChEBI" title="ChEBI">ChEBI</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="www.ebi.ac.uk"><a rel="nofollow" class="external text" href="https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:17336">CHEBI:17336</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/ChEMBL" title="ChEMBL">ChEMBL</a></th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="www.ebi.ac.uk"><a rel="nofollow" class="external text" href="https://www.ebi.ac.uk/chembl/explore/compound/ChEMBL986">ChEMBL986</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/ECHA_InfoCard" class="mw-redirect" title="ECHA InfoCard"><span title="echa.europa.eu">ECHA InfoCard</span></a></th><td class="infobox-data"><a rel="nofollow" class="external text" href="https://echa.europa.eu/substance-information/-/substanceinfo/100.031.195">100.031.195</a> <span class="mw-valign-text-top noprint" typeof="mw:File/Frameless"><a href="https://www.wikidata.org/wiki/Q18225#P2566" title="Edit this at Wikidata"><img alt="Edit this at Wikidata" src="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/10px-OOjs_UI_icon_edit-ltr-progressive.svg.png" decoding="async" width="10" height="10" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/15px-OOjs_UI_icon_edit-ltr-progressive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/20px-OOjs_UI_icon_edit-ltr-progressive.svg.png 2x" data-file-width="20" data-file-height="20" /></a></span></td></tr><tr><th colspan="2" class="infobox-header" style="background:#ddd;color:inherit;">Chemical and physical data</th></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Chemical_formula" title="Chemical formula">Formula</a></th><td class="infobox-data"><span title="Carbon">C</span><sub>20</sub><span title="Hydrogen">H</span><sub>30</sub><span title="Oxygen">O</span></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Molar_mass" title="Molar mass">Molar mass</a></th><td class="infobox-data"><span class="nowrap"><span data-sort-value="7002286459000000000♠"></span>286.459</span> g·mol<sup>−1</sup></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;">3D model (<a href="/wiki/JSmol" class="mw-redirect" title="JSmol">JSmol</a>)</th><td class="infobox-data"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="chemapps.stolaf.edu (3D interactive model)"><a rel="nofollow" class="external text" href="https://chemapps.stolaf.edu/jmol/jmol.php?model=OC%2FC%3DC%28C%29%2FC%3DC%2FC%3DC%28C%29%2FC%3DC%2FC1%3DC%28C%29%2FCCCC1%28C%29C">Interactive image</a></span></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Melting_point" title="Melting point">Melting point</a></th><td class="infobox-data">62–64 °C (144–147 °F)</td></tr><tr><th scope="row" class="infobox-label" style="line-height:1.2em;"><a href="/wiki/Boiling_point" title="Boiling point">Boiling point</a></th><td class="infobox-data">137–138 °C (279–280 °F) (<span class="nowrap"><span data-sort-value="6994100000000000000♠"></span>10<sup>−6</sup> mm Hg</span>)</td></tr><tr><td colspan="2" class="infobox-full-data"><div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold;"><div><a href="/wiki/Simplified_molecular-input_line-entry_system" class="mw-redirect" title="Simplified molecular-input line-entry system">SMILES</a></div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit; list-style: none; margin-left: 0; word-break:break-all;"><li style="line-height: inherit; margin: 0"><div style="word-wrap:break-word; text-indent:-1.5em; text-align:left; padding-left:1.5em; font-size:97%; line-height:120%;">OC/C=C(C)/C=C/C=C(C)/C=C/C1=C(C)/CCCC1(C)C</div></li></ul> </div></td></tr><tr><td colspan="2" class="infobox-full-data"><div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold;"><div><a href="/wiki/International_Chemical_Identifier" title="International Chemical Identifier">InChI</a></div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit; list-style: none; margin-left: 0; word-break:break-all;"><li style="line-height: inherit; margin: 0"><div style="word-wrap:break-word; text-indent:-1.5em; text-align:left; padding-left:1.5em; font-size:97%; line-height:120%;">InChI=1S/C20H30O/c1-16(8-6-9-17(2)13-15-21)11-12-19-18(3)10-7-14-20(19,4)5/h6,8-9,11-13,21H,7,10,14-15H2,1-5H3/b9-6+,12-11+,16-8+,17-13+</div></li><li style="line-height: inherit; margin: 0"><div style="word-wrap:break-word; text-indent:-1.5em; text-align:left; padding-left:1.5em; font-size:97%; line-height:120%;">Key:FPIPGXGPPPQFEQ-OVSJKPMPSA-N</div></li></ul> </div></td></tr></tbody></table> <p><b>Vitamin A</b> is a <a href="/wiki/Fat-soluble" class="mw-redirect" title="Fat-soluble">fat-soluble</a> <a href="/wiki/Vitamin" title="Vitamin">vitamin</a> that is an <a href="/wiki/Essential_nutrient" class="mw-redirect" title="Essential nutrient">essential nutrient</a>. The term "vitamin A" encompasses a group of chemically related <a href="/wiki/Organic_compounds" class="mw-redirect" title="Organic compounds">organic compounds</a> that includes <a href="/wiki/Retinol" title="Retinol">retinol</a>, retinyl <a href="/wiki/Ester" title="Ester">esters</a>, and several <a href="/wiki/Provitamin" title="Provitamin">provitamin</a> (precursor) <a href="/wiki/Carotenoid" title="Carotenoid">carotenoids</a>, most notably <a href="/wiki/%CE%92-Carotene" title="Β-Carotene">β-carotene</a> (<i>beta</i>-<a href="/wiki/Carotene" title="Carotene">carotene</a>).<sup id="cite_ref-ods_3-0" class="reference"><a href="#cite_note-ods-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-lpi_4-0" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-DRI_VitA_5-0" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-PKIN2020VitA_6-0" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Vitamin A has multiple functions: growth during <a href="/wiki/Embryo" title="Embryo">embryo</a> development, maintaining the <a href="/wiki/Immune_system" title="Immune system">immune system</a>, and healthy vision. For aiding vision specifically, it combines with the protein <a href="/wiki/Opsin" title="Opsin">opsin</a> to form <a href="/wiki/Rhodopsin" title="Rhodopsin">rhodopsin</a>, the light-absorbing molecule necessary for both low-light (<a href="/wiki/Scotopic" class="mw-redirect" title="Scotopic">scotopic</a> vision) and <a href="/wiki/Color_vision" title="Color vision">color vision</a>.<sup id="cite_ref-Wolf2001_7-0" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>Vitamin A occurs as two principal forms in foods: A) retinoids, found in <a href="/wiki/Animal_source_foods" title="Animal source foods">animal-sourced foods</a>, either as retinol or bound to a <a href="/wiki/Fatty_acid" title="Fatty acid">fatty acid</a> to become a retinyl ester, and B) the carotenoids <a href="/wiki/%CE%91-Carotene" title="Α-Carotene">α-carotene</a> (<i>alpha</i>-carotene), β-carotene, <a href="/wiki/%CE%93-Carotene" title="Γ-Carotene">γ-carotene</a> (<i>gamma</i>-carotene), and the <a href="/wiki/Xanthophyll" title="Xanthophyll">xanthophyll</a> <a href="/wiki/Beta-cryptoxanthin" class="mw-redirect" title="Beta-cryptoxanthin">beta-cryptoxanthin</a> (all of which contain β-<a href="/wiki/Ionone" title="Ionone">ionone</a> rings) that function as provitamin A in <a href="/wiki/Herbivore" title="Herbivore">herbivore</a> and <a href="/wiki/Omnivore" title="Omnivore">omnivore</a> animals which possess the <a href="/wiki/Enzyme" title="Enzyme">enzymes</a> that cleave and convert provitamin carotenoids to retinol.<sup id="cite_ref-Wu2016_8-0" class="reference"><a href="#cite_note-Wu2016-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Some <a href="/wiki/Carnivore" title="Carnivore">carnivore</a> species lack this enzyme. The other carotenoids do not have retinoid activity.<sup id="cite_ref-PKIN2020VitA_6-1" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p>Dietary retinol is absorbed from the <a href="/wiki/Digestive_tract" class="mw-redirect" title="Digestive tract">digestive tract</a> via <a href="/wiki/Passive_transport" title="Passive transport">passive diffusion</a>. Unlike retinol, β-carotene is taken up by <a href="/wiki/Enterocyte" title="Enterocyte">enterocytes</a> by the membrane transporter protein <a href="/wiki/SCARB1" title="SCARB1">scavenger receptor B1</a> (SCARB1), which is upregulated in times of <a href="/wiki/Vitamin_A_deficiency" title="Vitamin A deficiency">vitamin A deficiency</a> (VAD).<sup id="cite_ref-PKIN2020VitA_6-2" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Retinol is stored in <a href="/wiki/Lipid_droplet" title="Lipid droplet">lipid droplets</a> in the <a href="/wiki/Liver" title="Liver">liver</a>. A high capacity for long-term storage of retinol means that well-nourished humans can go months on a vitamin A-deficient diet, while maintaining <a href="/wiki/Blood" title="Blood">blood</a> levels in the normal range.<sup id="cite_ref-lpi_4-1" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Only when the liver stores are nearly depleted will signs and symptoms of deficiency show.<sup id="cite_ref-lpi_4-2" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Retinol is reversibly converted to <a href="/wiki/Retinal" title="Retinal">retinal</a>, then irreversibly to <a href="/wiki/Retinoic_acid" title="Retinoic acid">retinoic acid</a>, which activates hundreds of <a href="/wiki/Gene" title="Gene">genes</a>.<sup id="cite_ref-Kedish2016_9-0" class="reference"><a href="#cite_note-Kedish2016-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p>Vitamin A deficiency is common in developing countries, especially in <a href="/wiki/Sub-Saharan_Africa" title="Sub-Saharan Africa">Sub-Saharan Africa</a> and <a href="/wiki/Southeast_Asia" title="Southeast Asia">Southeast Asia</a>. Deficiency can occur at any age but is most common in pre-school age children and pregnant women, the latter due to a need to transfer retinol to the fetus. Vitamin A deficiency is estimated to affect approximately one-third of children under the age of five around the world, resulting in hundreds of thousands of cases of <a href="/wiki/Visual_impairment" title="Visual impairment">blindness</a> and deaths from childhood diseases because of immune system failure.<sup id="cite_ref-UNICEFvitaminA_10-0" class="reference"><a href="#cite_note-UNICEFvitaminA-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> Reversible <a href="/wiki/Nyctalopia" title="Nyctalopia">night blindness</a> is an early indicator of low vitamin A status. Plasma retinol is used as a <a href="/wiki/Biomarker" title="Biomarker">biomarker</a> to confirm vitamin A deficiency. Breast milk retinol can indicate a deficiency in nursing mothers. Neither of these measures indicates the status of liver reserves.<sup id="cite_ref-PKIN2020VitA_6-3" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p>The <a href="/wiki/European_Union" title="European Union">European Union</a> and various countries have set recommendations for dietary intake, and upper limits for safe intake. Vitamin A toxicity also referred to as <a href="/wiki/Hypervitaminosis_A" title="Hypervitaminosis A">hypervitaminosis A</a>, occurs when there is too much vitamin A accumulating in the body. Symptoms may include nervous system effects, liver abnormalities, <a href="/wiki/Fatigue" title="Fatigue">fatigue</a>, muscle weakness, bone and skin changes, and others. The adverse effects of both acute and chronic toxicity are reversed after consumption of high dose supplements is stopped.<sup id="cite_ref-PKIN2020VitA_6-4" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Definition">Definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=1" title="Edit section: Definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A is a <a href="/wiki/Fat-soluble" class="mw-redirect" title="Fat-soluble">fat-soluble</a> <a href="/wiki/Vitamin" title="Vitamin">vitamin</a>, a category that also includes <a href="/wiki/Vitamin_D" title="Vitamin D">vitamins D</a>, <a href="/wiki/Vitamin_E" title="Vitamin E">E</a> and <a href="/wiki/Vitamin_K" title="Vitamin K">K</a>. The vitamin encompasses several chemically related naturally occurring compounds or metabolites, i.e., <a href="/wiki/Vitamer" title="Vitamer">vitamers</a>, that all contain a β-<a href="/wiki/Ionone" title="Ionone">ionone</a> ring.<sup id="cite_ref-lpi_4-3" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> The primary dietary form is <a href="/wiki/Retinol" title="Retinol">retinol</a>, which may have a <a href="/wiki/Fatty_acid" title="Fatty acid">fatty acid</a> molecule attached, creating a retinyl <a href="/wiki/Ester" title="Ester">ester</a>, when stored in the liver. Retinol – the transport and storage form of vitamin A – is interconvertible with <a href="/wiki/Retinal" title="Retinal">retinal</a>, catalyzed to retinal by <a href="/wiki/Retinol_dehydrogenase" title="Retinol dehydrogenase">retinol dehydrogenases</a> and back to retinol by retinaldehyde reductases.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <dl><dd>retinal + <a href="/wiki/Nicotinamide_adenine_dinucleotide_phosphate" title="Nicotinamide adenine dinucleotide phosphate">NADH</a> + H<sup>+</sup> ⇌ retinol + NAD<sup>+</sup></dd> <dd>retinol + <a href="/wiki/Nicotinamide_adenine_dinucleotide" title="Nicotinamide adenine dinucleotide">NAD</a><sup>+</sup> ⇌ retinal + NADH + H<sup>+</sup></dd></dl> <p>Retinal (also known as retinaldehyde) can be irreversibly converted to <i>all-trans</i>-<a href="/wiki/Retinoic_acid" title="Retinoic acid">retinoic acid</a> by the action of <a href="/wiki/Retinal_dehydrogenase" title="Retinal dehydrogenase">retinal dehydrogenase</a> </p> <dl><dd>retinal + NAD<sup>+</sup> + H<sub>2</sub>O → retinoic acid + NADH + H<sup>+</sup></dd></dl> <p>Retinoic acid is actively transported into the <a href="/wiki/Cell_nucleus" title="Cell nucleus">cell nucleus</a> by CRABp2 where it regulates thousands of genes by binding directly to gene targets via <a href="/wiki/Retinoic_acid_receptor_alpha" title="Retinoic acid receptor alpha">retinoic acid receptors</a>.<sup id="cite_ref-PKIN2020VitA_6-5" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p>In addition to retinol, retinal and retinoic acid, there are plant-, fungi- or bacteria-sourced <a href="/wiki/Carotenoid" title="Carotenoid">carotenoids</a> which can be metabolized to retinol, and are thus vitamin A vitamers.<sup id="cite_ref-PKIN2020Carotenoids_12-0" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>There are also what are referred to as 2nd, 3rd and 4th generation <a href="/wiki/Retinoid" title="Retinoid">retinoids</a> which are not considered vitamin A vitamers because they cannot be converted to retinol, retinal or <i>all-trans</i>-retinoic acid. Some are prescription drugs, oral or topical, for various indications. Examples are <a href="/wiki/Etretinate" title="Etretinate">etretinate</a>, <a href="/wiki/Acitretin" title="Acitretin">acitretin</a>, <a href="/wiki/Adapalene" title="Adapalene">adapalene</a>, <a href="/wiki/Bexarotene" title="Bexarotene">bexarotene</a>, <a href="/wiki/Tazarotene" title="Tazarotene">tazarotene</a> and <a href="/wiki/Trifarotene" title="Trifarotene">trifarotene</a>.<sup id="cite_ref-Becken2015_13-0" class="reference"><a href="#cite_note-Becken2015-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Monograph_14-0" class="reference"><a href="#cite_note-Monograph-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Absorption,_metabolism_and_excretion"><span id="Absorption.2C_metabolism_and_excretion"></span>Absorption, metabolism and excretion</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=2" title="Edit section: Absorption, metabolism and excretion"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Retinyl esters from <a href="/wiki/Animal_source_foods" title="Animal source foods">animal-sourced foods</a> (or synthesized for dietary supplements for humans and domesticated animals) are acted upon by retinyl ester hydrolases in the <a href="/wiki/Lumen_(anatomy)" title="Lumen (anatomy)">lumen</a> of the small intestine to release free retinol. Retinol enters <a href="/wiki/Enterocyte" title="Enterocyte">enterocytes</a> by <a href="/wiki/Passive_transport" title="Passive transport">passive diffusion</a>. Absorption efficiency is in the range of 70 to 90%. Humans are at risk for acute or chronic vitamin A toxicity because there are no mechanisms to suppress absorption or excrete the excess in urine.<sup id="cite_ref-DRI_VitA_5-1" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Within the cell, retinol is there bound to <a href="/wiki/RBP2" title="RBP2">retinol binding protein 2</a> (RBP2). It is then enzymatically re-esterified by the action of <a href="/wiki/Lecithin_retinol_acyltransferase" title="Lecithin retinol acyltransferase">lecithin retinol acyltransferase</a> and incorporated into <a href="/wiki/Chylomicron" title="Chylomicron">chylomicrons</a> that are secreted into the <a href="/wiki/Lymphatic_system" title="Lymphatic system">lymphatic system</a>. </p><p>Unlike retinol, <a href="/wiki/%CE%92-Carotene" title="Β-Carotene">β-carotene</a> is taken up by enterocytes by the membrane transporter protein <a href="/wiki/SCARB1" title="SCARB1">scavenger receptor B1</a> (SCARB1). The protein is upregulated in times of vitamin A deficiency. If vitamin A status is in the normal range, SCARB1 is downregulated, reducing absorption.<sup id="cite_ref-PKIN2020VitA_6-6" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Also downregulated is the <a href="/wiki/Enzyme" title="Enzyme">enzyme</a> <a href="/wiki/Beta-carotene_15,15%27-dioxygenase" title="Beta-carotene 15,15'-dioxygenase">beta-carotene 15,15'-dioxygenase</a> (formerly known as beta-<a href="/wiki/Carotene" title="Carotene">carotene</a> 15,15'-monooxygenase) coded for by the BCMO1 gene, responsible for symmetrically cleaving β-carotene into retinal.<sup id="cite_ref-Wu2016_8-1" class="reference"><a href="#cite_note-Wu2016-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Absorbed β-carotene is either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to RBP2. After a meal, roughly two-thirds of the chylomicrons are taken up by the liver with the remainder delivered to peripheral tissues. Peripheral tissues also can convert chylomicron β-carotene to retinol.<sup id="cite_ref-PKIN2020VitA_6-7" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Chel2016_15-0" class="reference"><a href="#cite_note-Chel2016-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p><p>The capacity to store retinol in the liver means that well-nourished humans can go months on a vitamin A deficient diet without manifesting signs and symptoms of deficiency. Two liver cell types are responsible for storage and release: <a href="/wiki/Hepatocyte" title="Hepatocyte">hepatocytes</a> and <a href="/wiki/Hepatic_stellate_cell" title="Hepatic stellate cell">hepatic stellate cells</a> (HSCs). Hepatocytes take up the lipid-rich chylomicrons, bind retinol to <a href="/wiki/RBP4" class="mw-redirect" title="RBP4">retinol-binding protein 4</a> (RBP4), and transfer the retinol-RBP4 to HSCs for storage in lipid droplets as retinyl esters. Mobilization reverses the process: retinyl ester hydrolase releases free retinol which is transferred to hepatocytes, bound to RBP4, and put into <a href="/wiki/Blood" title="Blood">blood</a> circulation. Other than either after a meal or when consumption of large amounts exceeds liver storage capacity, more than 95% of retinol in circulation is bound to RBP4.<sup id="cite_ref-Chel2016_15-1" class="reference"><a href="#cite_note-Chel2016-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Carnivores">Carnivores</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=3" title="Edit section: Carnivores"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Strict <a href="/wiki/Carnivore" title="Carnivore">carnivores</a> manage vitamin A differently than <a href="/wiki/Omnivore" title="Omnivore">omnivores</a> and <a href="/wiki/Herbivore" title="Herbivore">herbivores</a>. Carnivores are more tolerant of high intakes of retinol because those species have the ability to excrete retinol and retinyl esters in urine. Carnivores also have the ability to store more in the liver, due to a higher ratio of liver HSCs to hepatocytes compared to omnivores and herbivores. For humans, liver content can range from 20 to 30 μg/gram wet weight. Notoriously, <a href="/wiki/Polar_bear" title="Polar bear">polar bear</a> liver is acutely toxic to humans because content has been reported in range of 2,215 to 10,400 μg/g wet weight.<sup id="cite_ref-Green2016_16-0" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> As noted, in humans, retinol circulates bound to RBP4. Carnivores maintain R-RBP4 within a tight range while also having retinyl esters in circulation. Bound retinol is delivered to cells while the esters are excreted in the urine.<sup id="cite_ref-Green2016_16-1" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> In general, carnivore species are poor converters of ionone-containing carotenoids, and pure carnivores such as <a href="/wiki/Felidae" title="Felidae">felidae</a> (cats) lack the cleaving enzyme entirely. They must have retinol or retinyl esters in their diet.<sup id="cite_ref-Green2016_16-2" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Herbivores">Herbivores</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=4" title="Edit section: Herbivores"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Herbivores consume ionone-containing carotenoids and convert those to retinal. Some species, including cattle and horses, have measurable amounts of β-carotene circulating in the blood, and stored in <a href="/wiki/Body_fat" class="mw-redirect" title="Body fat">body fat</a>, creating yellow <a href="/wiki/Fat_cell" class="mw-redirect" title="Fat cell">fat cells</a>. Most species have <a href="/wiki/White_fat" class="mw-redirect" title="White fat">white fat</a> and no β-carotene in circulation.<sup id="cite_ref-Green2016_16-3" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Activation_and_excretion">Activation and excretion</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=5" title="Edit section: Activation and excretion"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In the liver and peripheral tissues of humans, retinol is reversibly converted to retinal by the action of alcohol dehydrogenases, which are also responsible for the conversion of <a href="/wiki/Ethanol" title="Ethanol">ethanol</a> to <a href="/wiki/Acetaldehyde" title="Acetaldehyde">acetaldehyde</a>. Retinal is irreversibly oxidized to retinoic acid (RA) by the action of aldehyde dehydrogenases. RA regulates the activation or deactivation of genes. The oxidative degradation of RA is induced by RA – its presence triggers its removal, making for a short-acting gene transcription signal. This deactivation is mediated by a <a href="/wiki/Cytochrome_P450" title="Cytochrome P450">cytochrome P450</a> (CYP) enzyme system, specifically enzymes <a href="/wiki/CYP26A1" title="CYP26A1">CYP26A1</a>, <a href="/wiki/CYP26B1" title="CYP26B1">CYP26B1</a> and <a href="/wiki/CYP26C1" title="CYP26C1">CYP26C1</a>. CYP26A1 is the predominant form in the human liver; all other human adult tissues contained higher levels of CYP26B1. CYP26C1 is expressed mainly during embryonic development. All three convert retinoic acid into 4-oxo-RA, 4-OH-RA and 18-OH-RA. <a href="/wiki/Glucuronic_acid" title="Glucuronic acid">Glucuronic acid</a> forms water-soluble glucuronide conjugates with the oxidized metabolites, which are then excreted in urine and feces.<sup id="cite_ref-Kedish2016_9-1" class="reference"><a href="#cite_note-Kedish2016-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Metabolic_functions">Metabolic functions</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=6" title="Edit section: Metabolic functions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Vitamin_A_deficiency" title="Vitamin A deficiency">Vitamin A deficiency</a></div> <p>Other than for vision, the metabolic functions of vitamin A are mediated by <a href="/wiki/Retinoic_acid" title="Retinoic acid"><i>all-trans</i>-retinoic acid (RA)</a>. The formation of RA from retinal is irreversible. To prevent accumulation of RA it is oxidized and eliminated fairly quickly, i.e., has a short half-life. Three cytochromes catalyze the oxidation of retinoic acid. The genes for Cyp26A1, Cyp26B1 and Cyp26C1 are induced by high levels of RA, providing a self-regulating feedback loop.<sup id="cite_ref-Roberts2020_17-0" class="reference"><a href="#cite_note-Roberts2020-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Isoherr2019_18-0" class="reference"><a href="#cite_note-Isoherr2019-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Vision_and_eye_health">Vision and eye health</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=7" title="Edit section: Vision and eye health"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A status involves eye health via two separate functions. Retinal is an essential factor in <a href="/wiki/Rod_cell" title="Rod cell">rod cells</a> and <a href="/wiki/Cone_cell" title="Cone cell">cone cells</a> in the retina responding to light exposure by sending nerve signals to the brain. An early sign of vitamin A deficiency is night blindness.<sup id="cite_ref-PKIN2020VitA_6-8" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Vitamin A in the form of retinoic acid is essential to normal epithelial cell functions. Severe vitamin A deficiency, common in infants and young children in southeast Asia causes <a href="/wiki/Xerophthalmia" title="Xerophthalmia">xerophthalmia</a> characterized by dryness of the conjunctival epithelium and cornea. Untreated, xerophthalmia progresses to corneal ulceration and blindness.<sup id="cite_ref-Whitcher2001_19-0" class="reference"><a href="#cite_note-Whitcher2001-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Vision">Vision</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=8" title="Edit section: Vision"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Visual_cycle" title="Visual cycle">visual cycle</a></div> <p>The role of vitamin A in the visual cycle is specifically related to the retinal compound. Retinol is converted by the enzyme <a href="/wiki/RPE65" title="RPE65">RPE65</a> within the retinal pigment epithelium into 11-<i>cis</i>-retinal. Within the eye, 11-<i>cis</i>-retinal is bound to the protein <a href="/wiki/Opsin" title="Opsin">opsin</a> to form <a href="/wiki/Rhodopsin" title="Rhodopsin">rhodopsin</a> in rod cells and <a href="/wiki/Iodopsin" class="mw-redirect" title="Iodopsin">iodopsin</a> in cone cells. As light enters the eye, the 11-<i>cis</i>-retinal is isomerized to the <i>all-trans</i> form. The <i>all-trans</i>-retinal dissociates from the opsin in a series of steps called photo-bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. After separating from opsin, the <i>all-trans</i>-retinal is recycled and converted back to the 11-<i>cis</i>-retinal form by a series of enzymatic reactions, which then completes the cycle by binding to opsin to reform rhodopsin in the retina.<sup id="cite_ref-PKIN2020VitA_6-9" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> In addition, some of the <i>all-trans</i>-retinal may be converted to <i>all-trans</i>-retinol form and then transported with an interphotoreceptor retinol-binding protein to the retinal pigmented epithelial cells. Further esterification into <i>all-trans</i>-retinyl esters allow for storage of <i>all-trans</i>-retinol within the pigment epithelial cells to be reused when needed. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin, and will lead to one of the first symptoms, night blindness.<sup id="cite_ref-PKIN2020VitA_6-10" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Combs2008_20-0" class="reference"><a href="#cite_note-Combs2008-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Miller_21-0" class="reference"><a href="#cite_note-Miller-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Night_blindness">Night blindness</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=9" title="Edit section: Night blindness"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Nyctalopia" title="Nyctalopia">Nyctalopia</a></div> <p>Vitamin A deficiency-caused <a href="/wiki/Nyctalopia" title="Nyctalopia">night blindness</a> is a reversible difficulty for the eyes to adjust to dim light. It is common in young children who have a diet inadequate in retinol and β-carotene. A process called <a href="/wiki/Adaptation_(eye)" title="Adaptation (eye)">dark adaptation</a> typically causes an increase in photopigment amounts in response to low levels of illumination. This increases light sensitivity by up to 100,000 times compared to normal daylight conditions. Significant improvement in night vision takes place within ten minutes, but the process can take up to two hours to reach maximal effect.<sup id="cite_ref-Wolf2001_7-1" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> People expecting to work in a dark environment wore red-tinted goggles or were in a red light environment to not reverse the adaptation because red light does not deplete rhodopsin versus what occurs with yellow or green light.<sup id="cite_ref-Miller_21-1" class="reference"><a href="#cite_note-Miller-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Xerophthalmia_and_childhood_blindness">Xerophthalmia and childhood blindness</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=10" title="Edit section: Xerophthalmia and childhood blindness"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Xerophthalmia" title="Xerophthalmia">Xerophthalmia</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Typical_location_of_Bitot%27s_spots.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/79/Typical_location_of_Bitot%27s_spots.jpg/220px-Typical_location_of_Bitot%27s_spots.jpg" decoding="async" width="220" height="136" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/79/Typical_location_of_Bitot%27s_spots.jpg/330px-Typical_location_of_Bitot%27s_spots.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/79/Typical_location_of_Bitot%27s_spots.jpg/440px-Typical_location_of_Bitot%27s_spots.jpg 2x" data-file-width="653" data-file-height="405" /></a><figcaption>Typical location of Bitot's spots</figcaption></figure> <p>Xerophthalmia, caused by a severe vitamin A deficiency, is described by pathologic dryness of the conjunctival epithelium and cornea. The conjunctiva becomes dry, thick, and wrinkled. Indicative is the appearance of Bitot's spots, which are clumps of keratin debris that build up inside the conjunctiva. If untreated, xerophthalmia can lead to dry eye syndrome, <a href="/wiki/Corneal_ulceration" class="mw-redirect" title="Corneal ulceration">corneal ulceration</a> and ultimately to blindness as a result of cornea and retina damage. Although xerophthalmia is an eye-related issue, prevention (and reversal) are functions of retinoic acid having been synthesized from retinal rather than the 11-<i>cis</i>-retinal to rhodopsin cycle.<sup id="cite_ref-Akhtar2013_22-0" class="reference"><a href="#cite_note-Akhtar2013-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> </p><p>Throughout southeast Asia, estimates are that more than half of children under the age of six years have subclinical vitamin A deficiency and night blindness, with progression to xerophthalmia being the leading cause of preventable childhood blindness.<sup id="cite_ref-Akhtar2013_22-1" class="reference"><a href="#cite_note-Akhtar2013-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> Estimates are that each year there are 350,000 cases of childhood blindness due to vitamin A deficiency.<sup id="cite_ref-Whitcher2001_19-1" class="reference"><a href="#cite_note-Whitcher2001-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> The causes are vitamin A deficiency during pregnancy, followed by low transfer of vitamin A during lactation and infant/child diets low in vitamin A or β-carotene.<sup id="cite_ref-Akhtar2013_22-2" class="reference"><a href="#cite_note-Akhtar2013-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Whitcher2001_19-2" class="reference"><a href="#cite_note-Whitcher2001-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Prevalence" title="Prevalence">prevalence</a> of pre-school age children who are blind due to vitamin A deficiency is lower than expected from <a href="/wiki/Incidence_(epidemiology)" title="Incidence (epidemiology)">incidence of new cases</a> only because childhood vitamin A deficiency significantly increases all-cause mortality.<sup id="cite_ref-Whitcher2001_19-3" class="reference"><a href="#cite_note-Whitcher2001-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p><p>According to a 2017 Cochrane review, vitamin A deficiency, using serum retinol less than 0.70 μmol/L as a criterion, is a major public health problem affecting an estimated 190 million children under five years of age in low- and middle-income countries, primarily in Sub-Saharan Africa and Southeast Asia. In lieu of or in combination with food fortification programs, many countries have implemented public health programs in which children are periodically given very large oral doses of synthetic vitamin A, usually retinyl palmitate, as a means of preventing and treating vitamin A deficiency. Doses were 50,000 to 100,000 IU (<a href="/wiki/International_unit" title="International unit">International units</a>) for children aged 6 to 11 months and 100,000 to 200,000 IU for children aged 12 months to five years, the latter typically every four to six months. In addition to a 24% reduction in all-cause mortality, eye-related results were reported. Prevalence of Bitot's spots at follow-up were reduced by 58%, night blindness by 68%, xerophthalmia by 69%.<sup id="cite_ref-Imdad2017_23-0" class="reference"><a href="#cite_note-Imdad2017-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Gene_regulation">Gene regulation</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=11" title="Edit section: Gene regulation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>RA regulates gene transcription by binding to nuclear receptors known as retinoic acid receptors (RARs; RARα, RARβ, RARγ) which are bound to <a href="/wiki/DNA" title="DNA">DNA</a> as heterodimers with retinoid "X" receptors (RXRs; RXRα, RXRβ, RXRγ). RARs and RXRs must dimerize before they can bind to the DNA. Expression of more than 500 genes is responsive to retinoic acid.<sup id="cite_ref-PKIN2020VitA_6-11" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> RAR-RXR heterodimers recognize retinoic acid response elements on DNA.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> Upon binding retinoic acid, the receptors undergo a conformational change that causes co-repressors to dissociate from the receptors. Coactivators can then bind to the receptor complex, which may help to loosen the chromatin structure from the histones or may interact with the transcriptional machinery.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> This response upregulates or downregulates the expression of target genes, including the genes that encode for the receptors themselves.<sup id="cite_ref-Combs2008_20-1" class="reference"><a href="#cite_note-Combs2008-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> To deactivate retinoic acid receptor signaling, three cytochromes (Cyp26A1, Cyp26B1 Cyp26C1) catalyze the oxidation of RA. The genes for these proteins are induced by high concentrations of RA, thus providing a regulatory feedback mechanism.<sup id="cite_ref-PKIN2020VitA_6-12" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Embryology">Embryology</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=12" title="Edit section: Embryology"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In vertebrates and invertebrate chordates, RA has a pivotal role during development. Altering levels of endogenous RA signaling during early embryology, either too low or too high, leads to birth defects,<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Marletaz2006_27-0" class="reference"><a href="#cite_note-Marletaz2006-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> including congenital vascular and cardiovascular defects.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> Of note, fetal alcohol spectrum disorder encompasses congenital anomalies, including craniofacial, auditory, and ocular defects, neurobehavioral anomalies and mental disabilities caused by maternal consumption of alcohol during pregnancy. It is proposed that in the embryo there is competition between acetaldehyde, an ethanol metabolite, and retinaldehyde (retinal) for aldehyde dehydrogenase activity, resulting in a retinoic acid deficiency, and attributing the congenital birth defects to the loss of RA activated gene activation. In support of this theory, ethanol-induced developmental defects can be ameliorated by increasing the levels of retinol or retinal.<sup id="cite_ref-Shabtai2018A_30-0" class="reference"><a href="#cite_note-Shabtai2018A-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> As for the risks of too much RA during embryogenesis, the prescription drugs <a href="/wiki/Tretinoin" title="Tretinoin">tretinoin</a> (<i>all-trans</i>-retinoic acid) and <a href="/wiki/Isotretinoin" title="Isotretinoin">isotretinoin</a> (13-cis-retinoic acid), used orally or topically for acne treatment, are labeled with <a href="/wiki/Boxed_warning" title="Boxed warning">boxed warnings</a> for pregnant women or women who may become pregnant, as they are known human teratogens.<sup id="cite_ref-Draghici2021_31-0" class="reference"><a href="#cite_note-Draghici2021-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Tretinoin_32-0" class="reference"><a href="#cite_note-Tretinoin-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Immune_functions">Immune functions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=13" title="Edit section: Immune functions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A deficiency has been linked to compromised resistance to infectious diseases.<sup id="cite_ref-Ross2012_33-0" class="reference"><a href="#cite_note-Ross2012-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Pino2010_34-0" class="reference"><a href="#cite_note-Pino2010-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> In countries where early childhood vitamin A deficiency is common, vitamin A supplementation public health programs initiated in the 1980s were shown to reduce the incidence of diarrhea and measles, and all-cause mortality.<sup id="cite_ref-Imdad2017_23-1" class="reference"><a href="#cite_note-Imdad2017-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Brown2015_35-0" class="reference"><a href="#cite_note-Brown2015-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Guo2015_36-0" class="reference"><a href="#cite_note-Guo2015-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> Vitamin A deficiency also increases the risk of immune system over-reaction, leading to chronic inflammation in the intestinal system, stronger allergic reactions and autoimmune diseases.<sup id="cite_ref-Ross2012_33-1" class="reference"><a href="#cite_note-Ross2012-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Pino2010_34-1" class="reference"><a href="#cite_note-Pino2010-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Bono2016_37-0" class="reference"><a href="#cite_note-Bono2016-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Lymphocyte" title="Lymphocyte">Lymphocytes</a> and <a href="/wiki/Monocyte" title="Monocyte">monocytes</a> are types of <a href="/wiki/White_blood_cell" title="White blood cell">white blood cells</a> of the <a href="/wiki/Immune_system" title="Immune system">immune system</a>.<sup id="cite_ref-Janeway_38-0" class="reference"><a href="#cite_note-Janeway-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> Lymphocytes include <a href="/wiki/Natural_killer_cell" title="Natural killer cell">natural killer cells</a>, which function in <a href="/wiki/Innate_immune_system" title="Innate immune system">innate immunity</a>, <a href="/wiki/T_cell" title="T cell">T cells</a> for <a href="/wiki/Adaptive_immune_system" title="Adaptive immune system">adaptive cellular immunity</a> and <a href="/wiki/B_cell" title="B cell">B cells</a> for <a href="/wiki/Antibody" title="Antibody">antibody</a>-driven <a href="/wiki/Adaptive_immune_system" title="Adaptive immune system">adaptive humoral immunity</a>. Monocytes differentiate into <a href="/wiki/Macrophage" title="Macrophage">macrophages</a> and <a href="/wiki/Dendritic_cell" title="Dendritic cell">dendritic cells</a>. Some lymphocytes migrate to the <a href="/wiki/Thymus" title="Thymus">thymus</a> where they differentiate into several types of T cells, in some instances referred to as "killer" or "helper" T cells and further differentiate after leaving the thymus. Each subtype has functions driven by the types of <a href="/wiki/Cytokine" title="Cytokine">cytokines</a> secreted and organs to which the cells preferentially migrate, also described as trafficking or homing.<sup id="cite_ref-Omman_39-0" class="reference"><a href="#cite_note-Omman-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Cohn_40-0" class="reference"><a href="#cite_note-Cohn-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> </p><p>Retinoic acid (RA) triggers receptors in bone marrow, resulting in generation of new white blood cells.<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> RA regulates proliferation and differentiation of white blood cells, the directed movement of T cells to the <a href="/wiki/Gastrointestinal_tract" title="Gastrointestinal tract">intestinal system</a>, and to the up- and down-regulation of lymphocyte function.<sup id="cite_ref-Ross2012_33-2" class="reference"><a href="#cite_note-Ross2012-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Pino2010_34-2" class="reference"><a href="#cite_note-Pino2010-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Brown2015_35-1" class="reference"><a href="#cite_note-Brown2015-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Guo2015_36-1" class="reference"><a href="#cite_note-Guo2015-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Bono2016_37-1" class="reference"><a href="#cite_note-Bono2016-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Czarn2017_42-0" class="reference"><a href="#cite_note-Czarn2017-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> If RA is adequate, T helper cell subtype Th1 is suppressed and subtypes Th2, Th17 and iTreg (for regulatory) are induced. Dendritic cells located in intestinal tissue have enzymes that convert retinal to <i>all-trans</i>-retinoic acid, to be taken up by retinoic acid receptors on lymphocytes. The process triggers gene expression that leads to T cell types Th2, Th17 and iTreg moving to and taking up residence in <a href="/wiki/Mesenteric_lymph_node" class="mw-redirect" title="Mesenteric lymph node">mesenteric lymph nodes</a> and <a href="/wiki/Peyer%27s_patch" title="Peyer's patch">Peyer's patches</a>, respectively outside and on the inner wall of the small intestine.<sup id="cite_ref-Brown2015_35-2" class="reference"><a href="#cite_note-Brown2015-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Guo2015_36-2" class="reference"><a href="#cite_note-Guo2015-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> The net effect is a down-regulation of immune activity, seen as tolerance of food <a href="/wiki/Allergen" title="Allergen">allergens</a>, and tolerance of resident bacteria and other organisms in the <a href="/wiki/Microbiome" title="Microbiome">microbiome</a> of the large intestine.<sup id="cite_ref-Ross2012_33-3" class="reference"><a href="#cite_note-Ross2012-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Pino2010_34-3" class="reference"><a href="#cite_note-Pino2010-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Bono2016_37-2" class="reference"><a href="#cite_note-Bono2016-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> In a vitamin A deficient state, innate immunity is compromised and pro-inflammatory Th1 cells predominate.<sup id="cite_ref-Ross2012_33-4" class="reference"><a href="#cite_note-Ross2012-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Czarn2017_42-1" class="reference"><a href="#cite_note-Czarn2017-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Skin">Skin</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=14" title="Edit section: Skin"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Deficiencies in vitamin A have been linked to an increased susceptibility to skin infection and inflammation.<sup id="cite_ref-Roche2021_43-0" class="reference"><a href="#cite_note-Roche2021-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> Vitamin A appears to modulate the <a href="/wiki/Innate_immune_response" class="mw-redirect" title="Innate immune response">innate immune response</a> and maintains homeostasis of epithelial tissues and mucosa through its metabolite, retinoic acid (RA). As part of the innate immune system, <a href="/wiki/Toll-like_receptors" class="mw-redirect" title="Toll-like receptors">toll-like receptors</a> in skin cells respond to pathogens and cell damage by inducing a pro-inflammatory immune response which includes increased RA production.<sup id="cite_ref-Roche2021_43-1" class="reference"><a href="#cite_note-Roche2021-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> The epithelium of the skin encounters bacteria, fungi and viruses. Keratinocytes of the epidermal layer of the skin produce and secrete <a href="/wiki/Antimicrobial_peptides" title="Antimicrobial peptides">antimicrobial peptides</a> (AMPs). Production of AMPs <a href="/wiki/Resistin" title="Resistin">resistin</a> and <a href="/wiki/Cathelicidin" class="mw-redirect" title="Cathelicidin">cathelicidin</a>, are promoted by RA.<sup id="cite_ref-Roche2021_43-2" class="reference"><a href="#cite_note-Roche2021-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Units_of_measurement">Units of measurement</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=15" title="Edit section: Units of measurement"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>As some carotenoids can be converted into vitamin A, attempts have been made to determine how much of them in the diet is equivalent to a particular amount of retinol, so that comparisons can be made of the benefit of different foods. The situation can be confusing because the accepted equivalences have changed over time. </p><p>For many years, a system of equivalencies in which an <a href="/wiki/International_unit" title="International unit">international unit</a> (IU) was equal to 0.3 <a href="/wiki/Microgram" title="Microgram">μg</a> of retinol (~1 nmol), 0.6 μg of β-carotene, or 1.2 μg of other provitamin-A carotenoids was used.<sup id="cite_ref-44" class="reference"><a href="#cite_note-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> This relationship was alternatively expressed by the retinol equivalent (RE): one RE corresponded to 1 μg retinol, to 2 μg β-carotene dissolved in oil, to 6 μg β-carotene in foods, and to 12 μg of either <a href="/wiki/%CE%91-Carotene" title="Α-Carotene">α-carotene</a>, <a href="/wiki/%CE%93-Carotene" title="Γ-Carotene">γ-carotene</a>, or β-<a href="/wiki/Cryptoxanthin" class="mw-redirect" title="Cryptoxanthin">cryptoxanthin</a> in food. </p><p>Newer research has shown that the absorption of provitamin-A carotenoids is only half as much as previously thought. As a result, in 2001 the US <a href="/wiki/Institute_of_Medicine" class="mw-redirect" title="Institute of Medicine">Institute of Medicine</a> recommended a new unit, the retinol activity equivalent (RAE). Each μg RAE corresponds to 1 μg retinol, 2 μg of β-carotene in oil, 12 μg of "dietary" β-carotene, or 24 μg of the three other dietary provitamin-A carotenoids.<sup id="cite_ref-DRI_VitA_5-2" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th>Substance and its chemical environment (per 1 μg) </th> <th>IU (1989) </th> <th>μg <abbr title="retinol equivalent">RE</abbr> (1989)<sup id="cite_ref-DRI_VitA_5-3" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </th> <th>μg <abbr title="retinol activity equivalent">RAE</abbr> (2001)<sup id="cite_ref-DRI_VitA_5-4" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </th></tr> <tr> <td>Retinol </td> <td>3.33 </td> <td>1 </td> <td>1 </td></tr> <tr> <td><a href="/wiki/%CE%92-Carotene" title="Β-Carotene">β-Carotene</a>, dissolved in oil </td> <td>1.67 </td> <td>1/2 </td> <td>1/2 </td></tr> <tr> <td>β-Carotene, common dietary </td> <td>1.67 </td> <td>1/6 </td> <td>1/12 </td></tr> <tr> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"> <ul><li><a href="/wiki/%CE%91-Carotene" title="Α-Carotene">α-Carotene</a>, common dietary</li> <li><a href="/wiki/%CE%93-Carotene" title="Γ-Carotene">γ-Carotene</a>, common dietary</li> <li><a href="/wiki/Beta-cryptoxanthin" class="mw-redirect" title="Beta-cryptoxanthin">beta-Cryptoxanthin</a>, common dietary</li></ul> </div> </td> <td>0.83 </td> <td>1/12 </td> <td>1/24 </td></tr></tbody></table> <p>Animal models have shown that at the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is converted to retinal and then retinol. The first step of the conversion process consists of one molecule of β-carotene cleaved by the enzyme β-carotene-15, 15'-monooxygenase, which in humans and other mammalian species is encoded by the BCM01 gene,<sup id="cite_ref-Wu2016_8-2" class="reference"><a href="#cite_note-Wu2016-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> into two molecules of retinal. When plasma retinol is in the normal range, gene expression for SCARB1 and BC01 are suppressed, creating a feedback loop that suppresses β-carotene absorption and conversion.<sup id="cite_ref-PKIN2020Carotenoids_12-1" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Absorption suppression is not complete, as receptor 36 is not downregulated.<sup id="cite_ref-PKIN2020Carotenoids_12-2" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Dietary_recommendations">Dietary recommendations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=16" title="Edit section: Dietary recommendations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The US <a href="/wiki/National_Academy_of_Medicine" title="National Academy of Medicine">National Academy of Medicine</a> updated <a href="/wiki/Dietary_Reference_Intake" title="Dietary Reference Intake">Dietary Reference Intakes</a> (DRIs) in 2001 for vitamin A, which included Recommended Dietary Allowances (RDAs).<sup id="cite_ref-DRI_VitA_5-5" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> For infants up to 12 months, there was not sufficient information to establish an RDA, so Adequate Intake (AI) is shown instead. As for safety, <a href="/wiki/Tolerable_upper_intake_level" class="mw-redirect" title="Tolerable upper intake level">tolerable upper intake levels</a> (ULs) were also established. For ULs, carotenoids are not added when calculating total vitamin A intake for safety assessments.<sup id="cite_ref-DRI_VitA_5-6" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th colspan="2">Life stage group </th> <th>US RDAs or AIs<br /> (μg RAE/day)<sup id="cite_ref-DRI_VitA_5-7" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </th> <th>US Upper limits<br /> (μg/day)<sup id="cite_ref-DRI_VitA_5-8" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </th></tr> <tr> <td rowspan="2"><b>Infants</b> </td> <td>0–6 months</td> <td>400 (AI)</td> <td>600 </td></tr> <tr> <td>7–12 months</td> <td>500 (AI)</td> <td>600 </td></tr> <tr> <td rowspan="2"><b>Children</b> </td> <td>1–3 years</td> <td>300</td> <td>600 </td></tr> <tr> <td>4–8 years</td> <td>400</td> <td>900 </td></tr> <tr> <td rowspan="3"><b>Males</b> </td> <td>9–13 years</td> <td>600</td> <td>1700 </td></tr> <tr> <td>14–18 years</td> <td>900</td> <td>2800 </td></tr> <tr> <td>>19 years</td> <td>900</td> <td>3000 </td></tr> <tr> <td rowspan="3"><b>Females</b> </td> <td>9–13 years</td> <td>600</td> <td>1700 </td></tr> <tr> <td>14–18 years</td> <td>700</td> <td>2800 </td></tr> <tr> <td>>19 years</td> <td>700</td> <td>3000 </td></tr> <tr> <td rowspan="2"><b>Pregnancy</b> </td> <td><19 years</td> <td>750</td> <td>2800 </td></tr> <tr> <td>>19 years</td> <td>770</td> <td>3000 </td></tr> <tr> <td rowspan="2"><b>Lactation</b> </td> <td><19 years</td> <td>1200</td> <td>2800 </td></tr> <tr> <td>>19 years</td> <td>1300</td> <td>3000 </td></tr></tbody></table> <p>The <a href="/wiki/European_Food_Safety_Authority" title="European Food Safety Authority">European Food Safety Authority</a> (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For women and men of ages 15 and older, the PRIs are set respectively at 650 and 750 μg RE/day. PRI for pregnancy is 700 μg RE/day, for lactation 1300/day. For children of ages 1–14 years, the PRIs increase with age from 250 to 600 μg RE/day. These PRIs are similar to the US RDAs.<sup id="cite_ref-45" class="reference"><a href="#cite_note-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> The EFSA reviewed the same safety question as the United States, and set ULs at 800 for ages 1–3, 1100 for ages 4–6, 1500 for ages 7–10, 2000 for ages 11–14, 2600 for ages 15–17 and 3000 μg/day for ages 18 and older for preformed vitamin A, i.e., not including dietary contributions from carotenoids.<sup id="cite_ref-EFSA-UL_46-0" class="reference"><a href="#cite_note-EFSA-UL-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Safety">Safety</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=17" title="Edit section: Safety"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A toxicity (<a href="/wiki/Hypervitaminosis_A" title="Hypervitaminosis A">hypervitaminosis A</a>) occurs when too much vitamin A accumulates in the body. It comes from consumption of preformed vitamin A but not of carotenoids, as conversion of the latter to retinol is suppressed by the presence of adequate retinol. </p> <div class="mw-heading mw-heading4"><h4 id="Retinol_safety">Retinol safety</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=18" title="Edit section: Retinol safety"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Hypervitaminosis_A" title="Hypervitaminosis A">Hypervitaminosis A</a></div> <p>There are historical reports of acute hypervitaminosis from Arctic explorers consuming bearded seal or polar bear liver, both very rich sources of stored retinol,<sup id="cite_ref-47" class="reference"><a href="#cite_note-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> and there are also case reports of acute hypervitaminosis from consuming fish liver,<sup id="cite_ref-48" class="reference"><a href="#cite_note-48"><span class="cite-bracket">[</span>48<span class="cite-bracket">]</span></a></sup> but otherwise there is no risk from consuming too much via commonly consumed foods. Only consumption of retinol-containing dietary supplements can result in acute or chronic toxicity.<sup id="cite_ref-PKIN2020VitA_6-13" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Acute toxicity occurs after a single or short-term doses of greater than 150,000 μg. Symptoms include blurred vision, nausea, vomiting, dizziness and headache within 8 to 24 hours. For infants ages 0–6 months given an oral dose to prevent development of vitamin A deficiency, bulging skull fontanel was evident after 24 hours, usually resolved by 72 hours.<sup id="cite_ref-Imdad2016_49-0" class="reference"><a href="#cite_note-Imdad2016-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> Chronic toxicity may occur with long-term consumption of vitamin A at doses of 25,000–33,000 IU/day for several months.<sup id="cite_ref-lpi_4-4" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Excessive consumption of alcohol can lead to chronic toxicity at lower intakes.<sup id="cite_ref-ods_3-1" class="reference"><a href="#cite_note-ods-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Symptoms may include nervous system effects, liver abnormalities, <a href="/wiki/Fatigue" title="Fatigue">fatigue</a>, muscle weakness, bone and skin changes and others. The adverse effects of both acute and chronic toxicity are reversed after consumption is stopped.<sup id="cite_ref-DRI_VitA_5-9" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p><p>In 2001, for the purpose of determining ULs for adults, the US Institute of Medicine considered three primary adverse effects and settled on two: <a href="/wiki/Teratogen" class="mw-redirect" title="Teratogen">teratogenicity</a>, i.e., causing birth defects, and liver abnormalities. Reduced bone mineral density was considered, but dismissed because the human evidence was contradictory.<sup id="cite_ref-DRI_VitA_5-10" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> During pregnancy, especially during the first trimester, consumption of retinol in amounts exceeding 4,500 μg/day increased the risk of birth defects, but not below that amount, thus setting a "No-Observed Adverse-Effect Level" (NOAEL).<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Identifying_reliable_sources_(medicine)" title="Wikipedia:Identifying reliable sources (medicine)"><span title="Material near this tag needs references to reliable medical sources. (December 2024)">medical citation needed</span></a></i>]</sup> Given the quality of the clinical trial evidence, the NOAEL was divided by an uncertainty factor of 1.5 to set the UL for women of reproductive age at 3,000 μg/day of preformed vitamin A.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Identifying_reliable_sources_(medicine)" title="Wikipedia:Identifying reliable sources (medicine)"><span title="Material near this tag needs references to reliable medical sources. (December 2024)">medical citation needed</span></a></i>]</sup> For all other adults, liver abnormalities were detected at intakes above 14,000 μg/day.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Identifying_reliable_sources_(medicine)" title="Wikipedia:Identifying reliable sources (medicine)"><span title="Material near this tag needs references to reliable medical sources. (December 2024)">medical citation needed</span></a></i>]</sup> Given the weak quality of the clinical evidence, an uncertainty factor of 5 was used, and with rounding, the UL was set at 3,000 μg/day.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (December 2024)">citation needed</span></a></i>]</sup> </p><p>For children, ULs were extrapolated from the adult value, adjusted for relative body weight. For infants, several case studies reported adverse effects that include bulging fontanels, increased intracranial pressure, loss of appetite, hyperirritability and skin peeling after chronic ingestion of the order of 6,000 or more μg/day. Given the small database, an uncertainty factor of 10 divided into the "Lowest-Observed-Adverse-Effect Level" (LOAEL) led to a UL of 600 μg/day.<sup id="cite_ref-DRI_VitA_5-11" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="β-carotene_safety"><span id=".CE.B2-carotene_safety"></span>β-carotene safety</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=19" title="Edit section: β-carotene safety"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>No adverse effects other than <a href="/wiki/Carotenemia" class="mw-redirect" title="Carotenemia">carotenemia</a> have been reported for consumption of β-carotene rich foods. Supplementation with β-carotene does not cause hypervitaminosis A.<sup id="cite_ref-PKIN2020Carotenoids_12-3" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Two large clinical trials (ATBC and CARET) were conducted in tobacco smokers to see if years of β-carotene supplementation at 20 or 30 mg/day in oil-filled capsules would reduce the risk of lung cancer.<sup id="cite_ref-DRItextBetaCarotene_50-0" class="reference"><a href="#cite_note-DRItextBetaCarotene-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> These trials were implemented because observational studies had reported a lower incidence of lung cancer in tobacco smokers who had diets higher in β-carotene. Unexpectedly, high-dose β-carotene or retinol supplementation resulted in a higher incidence of lung cancer and of total mortality due to cardiac mortality.<sup id="cite_ref-51" class="reference"><a href="#cite_note-51"><span class="cite-bracket">[</span>51<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-PKIN2020Carotenoids_12-4" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Taking this and other evidence into consideration, the U.S. Institute of Medicine decided not to set a Tolerable Upper Intake Level (UL) for β-carotene.<sup id="cite_ref-PKIN2020Carotenoids_12-5" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-DRItextBetaCarotene_50-1" class="reference"><a href="#cite_note-DRItextBetaCarotene-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> The European Food Safety Authority, acting for the European Union, also decided not to set a UL for β-carotene.<sup id="cite_ref-EFSA-UL_46-1" class="reference"><a href="#cite_note-EFSA-UL-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Carrots.JPG" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Carrots.JPG/250px-Carrots.JPG" decoding="async" width="250" height="167" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Carrots.JPG/375px-Carrots.JPG 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Carrots.JPG/500px-Carrots.JPG 2x" data-file-width="3888" data-file-height="2592" /></a><figcaption><a href="/wiki/Carrot" title="Carrot">Carrots</a> are a rich source of β-carotene.</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Carotenosis">Carotenosis</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=20" title="Edit section: Carotenosis"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Carotenosis" title="Carotenosis">Carotenoderma</a>, also referred to as carotenemia, is a benign and reversible medical condition where an excess of dietary carotenoids results in orange discoloration of the outermost skin layer. It is associated with a high blood β-carotene value. This can occur after a month or two of consumption of β-carotene rich foods, such as carrots, carrot juice, tangerine juice, mangos, or in Africa, red palm oil. β-carotene dietary supplements can have the same effect. The discoloration extends to palms and soles of feet, but not to the <a href="/wiki/Sclera" title="Sclera">white of the eye</a>, which helps distinguish the condition from <a href="/wiki/Jaundice" title="Jaundice">jaundice</a>.<sup id="cite_ref-52" class="reference"><a href="#cite_note-52"><span class="cite-bracket">[</span>52<span class="cite-bracket">]</span></a></sup> Consumption of greater than 30 mg/day for a prolonged period has been confirmed as leading to carotenemia.<sup id="cite_ref-PKIN2020Carotenoids_12-6" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-53" class="reference"><a href="#cite_note-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="U.S._labeling">U.S. labeling</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=21" title="Edit section: U.S. labeling"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For vitamin A labeling purposes, 100% of the Daily Value was set at 5,000 IU, but it was revised to 900 μg RAE on 27 May 2016.<sup id="cite_ref-FedReg_54-0" class="reference"><a href="#cite_note-FedReg-54"><span class="cite-bracket">[</span>54<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-55" class="reference"><a href="#cite_note-55"><span class="cite-bracket">[</span>55<span class="cite-bracket">]</span></a></sup> A table of the old and new adult daily values is provided at <a href="/wiki/Reference_Daily_Intake" title="Reference Daily Intake">Reference Daily Intake</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Sources">Sources</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=22" title="Edit section: Sources"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable" style="float:right; clear:left; width:18em; text-align:center;"> <tbody><tr> <th>Food</th> <th> <p>μg <abbr title="retinol activity equivalent">RAE</abbr> (2001)<sup id="cite_ref-DRI_VitA_5-12" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> per 100 g<sup id="cite_ref-USDAContent_56-0" class="reference"><a href="#cite_note-USDAContent-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> </p> </th></tr> <tr> <td><a href="/wiki/Cod_liver_oil" title="Cod liver oil">cod liver oil</a></td> <td>30,000 </td></tr> <tr> <td><a href="/wiki/Liver_(food)" title="Liver (food)">beef liver</a> (cooked)</td> <td>4,970–21,145 </td></tr> <tr> <td><a href="/wiki/Liver_(food)" title="Liver (food)">chicken liver</a> (cooked)</td> <td>4,296 </td></tr> <tr> <td><a href="/wiki/Butter" title="Butter">butter</a> (stick)</td> <td>684 </td></tr> <tr> <td><a href="/wiki/Cheddar_cheese" title="Cheddar cheese">cheddar cheese</a></td> <td>316 </td></tr> <tr> <td><a href="/wiki/Egg_(food)" class="mw-redirect" title="Egg (food)">egg</a> (cooked)</td> <td>140 </td></tr> </tbody></table> <p>Vitamin A is found in many foods.<sup id="cite_ref-USDAContent_56-1" class="reference"><a href="#cite_note-USDAContent-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> Vitamin A in food exists either as preformed retinol – an active form of vitamin A – found in animal liver, dairy and egg products, and some fortified foods, or as provitamin A carotenoids, which are plant pigments digested into vitamin A after consuming carotenoid-rich plant foods, typically in red, orange, or yellow colors.<sup id="cite_ref-lpi_4-5" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Carotenoid pigments may be masked by <a href="/wiki/Chlorophyll" title="Chlorophyll">chlorophylls</a> in dark green leaf vegetables, such as spinach. The relatively low <a href="/wiki/Bioavailability" title="Bioavailability">bioavailability</a> of plant-food carotenoids results partly from binding to proteins – chopping, homogenizing or cooking disrupts the plant proteins, increasing provitamin A carotenoid bioavailability.<sup id="cite_ref-lpi_4-6" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Vegetarianism" title="Vegetarianism">Vegetarian</a> and <a href="/wiki/Veganism" title="Veganism">vegan</a> diets can provide sufficient vitamin A in the form of provitamin A carotenoids if the diet contains carrots, carrot juice, sweet potatoes, green leafy vegetables such as spinach and kale, and other carotenoid-rich foods. In the U.S., the average daily intake of β-carotene is in the range 2–7 mg.<sup id="cite_ref-57" class="reference"><a href="#cite_note-57"><span class="cite-bracket">[</span>57<span class="cite-bracket">]</span></a></sup> </p><p>Some <a href="/wiki/Food_fortification" title="Food fortification">manufactured foods</a> and dietary supplements are sources of vitamin A or β-carotene.<sup id="cite_ref-lpi_4-7" class="reference"><a href="#cite_note-lpi-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-DRI_VitA_5-13" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Fortification">Fortification</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=23" title="Edit section: Fortification"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Some countries require or recommend fortification of foods. As of January 2022, 37 countries, mostly in Sub-Saharan Africa, require food fortification of <a href="/wiki/Cooking_oil" title="Cooking oil">cooking oil</a>, rice, <a href="/wiki/Wheat" title="Wheat">wheat</a> flour or <a href="/wiki/Maize" title="Maize">maize</a> (corn) flour with vitamin A, usually as retinyl palmitate or retinyl acetate. Examples include Pakistan, oil, 11.7 mg/kg and Nigeria, oil, 6 mg/kg; wheat and maize flour, 2 mg/kg.<sup id="cite_ref-FortifMap_58-0" class="reference"><a href="#cite_note-FortifMap-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup> An additional 12 countries, mostly in southeast Asia, have a voluntary fortification program. For example, the government of India recommends 7.95 mg/kg in oil and 0.626 mg/kg for wheat flour and rice. However, compliance in countries with voluntary fortification is lower than countries with mandatory fortification.<sup id="cite_ref-FortifMap_58-1" class="reference"><a href="#cite_note-FortifMap-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup> No countries in Europe or North America fortify foods with vitamin A.<sup id="cite_ref-FortifMap_58-2" class="reference"><a href="#cite_note-FortifMap-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable" style="float:right; clear:left; width:18em; text-align:center;"> <tbody><tr> <th>Food </th> <th> <p>μg <abbr title="retinol activity equivalent">RAE</abbr> (2001)<sup id="cite_ref-DRI_VitA_5-14" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> per 100 g<sup id="cite_ref-USDAContent_56-2" class="reference"><a href="#cite_note-USDAContent-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup> </p> </th></tr> <tr> <td><a href="/wiki/Sweet_potato" title="Sweet potato">Sweet potato</a>, baked, no added <a href="/wiki/Fat" title="Fat">fat</a> </td> <td>957 </td></tr> <tr> <td><a href="/wiki/Carrot" title="Carrot">Carrot</a>, frozen, cooked, no added fat </td> <td>843 </td></tr> <tr> <td><a href="/wiki/Pumpkin" title="Pumpkin">Pumpkin</a>, canned, cooked </td> <td>767 </td></tr> <tr> <td><a href="/wiki/Spinach" title="Spinach">Spinach</a>, fresh, cooked, no added fat </td> <td>341 </td></tr> <tr> <td><a href="/wiki/Kale" title="Kale">Kale</a>, fresh, cooked, no added fat </td> <td>245 </td></tr> </tbody></table> <p>Other means of fortifying foods via genetic engineering have been explored. Research on rice began in 1982.<sup id="cite_ref-59" class="reference"><a href="#cite_note-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> The first field trials of golden rice cultivars were conducted in 2004.<sup id="cite_ref-60" class="reference"><a href="#cite_note-60"><span class="cite-bracket">[</span>60<span class="cite-bracket">]</span></a></sup> The result was "Golden Rice", a variety of <i><a href="/wiki/Oryza_sativa" title="Oryza sativa">Oryza sativa</a></i> rice produced through genetic engineering to <a href="/wiki/Biosynthesis" title="Biosynthesis">biosynthesize</a> β-carotene, a precursor of retinol, in the edible parts of rice.<sup id="cite_ref-61" class="reference"><a href="#cite_note-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-62" class="reference"><a href="#cite_note-62"><span class="cite-bracket">[</span>62<span class="cite-bracket">]</span></a></sup> In May 2018, regulatory agencies in the United States, Canada, Australia and New Zealand had concluded that Golden Rice met food safety standards.<sup id="cite_ref-63" class="reference"><a href="#cite_note-63"><span class="cite-bracket">[</span>63<span class="cite-bracket">]</span></a></sup> In July 2021, the Philippines became the first country to officially issue the biosafety permit for commercially propagating Golden Rice.<sup id="cite_ref-64" class="reference"><a href="#cite_note-64"><span class="cite-bracket">[</span>64<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-65" class="reference"><a href="#cite_note-65"><span class="cite-bracket">[</span>65<span class="cite-bracket">]</span></a></sup> However, in April 2023, the Supreme Court of the Philippines issued a <a href="/wiki/Writ_of_Kalikasan" title="Writ of Kalikasan">Writ of Kalikasan</a> ordering the Department of Agriculture to stop the commercial distribution of genetically modified rice in the country.<sup id="cite_ref-66" class="reference"><a href="#cite_note-66"><span class="cite-bracket">[</span>66<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Vitamin_A_supplementation_(VAS)"><span id="Vitamin_A_supplementation_.28VAS.29"></span>Vitamin A supplementation (VAS)</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=24" title="Edit section: Vitamin A supplementation (VAS)"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Vitamin_A_supplementation_coverage_rate_(children_ages_6-59_months),_OWID.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg/350px-Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg.png" decoding="async" width="350" height="247" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg/525px-Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg/700px-Vitamin_A_supplementation_coverage_rate_%28children_ages_6-59_months%29%2C_OWID.svg.png 2x" data-file-width="850" data-file-height="600" /></a><figcaption>Vitamin A supplementation coverage rate (children ages 6–59 months), 2014<sup id="cite_ref-67" class="reference"><a href="#cite_note-67"><span class="cite-bracket">[</span>67<span class="cite-bracket">]</span></a></sup></figcaption></figure> <p>Delivery of oral high-dose supplements remains the principal strategy for minimizing deficiency.<sup id="cite_ref-UNICEF_2007,_p.3_68-0" class="reference"><a href="#cite_note-UNICEF_2007,_p.3-68"><span class="cite-bracket">[</span>68<span class="cite-bracket">]</span></a></sup> As of 2017, more than 80 countries worldwide are implementing universal VAS programs targeted to children 6–59 months of age through semi-annual national campaigns.<sup id="cite_ref-Wirth2017_69-0" class="reference"><a href="#cite_note-Wirth2017-69"><span class="cite-bracket">[</span>69<span class="cite-bracket">]</span></a></sup> Doses in these programs are one dose of 50,000 or 100,000 IU for children aged 6 to 11 months and 100,000 to 200,000 IU for children aged 12 months to five years, every four to six months.<sup id="cite_ref-Imdad2017_23-2" class="reference"><a href="#cite_note-Imdad2017-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Deficiency">Deficiency</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=25" title="Edit section: Deficiency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Vitamin_A_deficiency" title="Vitamin A deficiency">Vitamin A deficiency</a></div> <div class="mw-heading mw-heading3"><h3 id="Primary_causes">Primary causes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=26" title="Edit section: Primary causes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A deficiency is common in <a href="/wiki/Developing_country" title="Developing country">developing countries</a>, especially in <a href="/wiki/Sub-Saharan_Africa" title="Sub-Saharan Africa">Sub-Saharan Africa</a> and <a href="/wiki/Southeast_Asia" title="Southeast Asia">Southeast Asia</a>. Deficiency can occur at any age, but is most common in pre-school-age children and pregnant women, the latter due to a need to transfer retinol to the fetus. The causes are low intake of retinol-containing, animal-sourced foods and low intake of carotene-containing, plant-sourced foods. Vitamin A deficiency is estimated to affect approximately one third of children under the age of five around the world,<sup id="cite_ref-70" class="reference"><a href="#cite_note-70"><span class="cite-bracket">[</span>70<span class="cite-bracket">]</span></a></sup> possibly leading to the deaths of 670,000 children under five annually.<sup id="cite_ref-71" class="reference"><a href="#cite_note-71"><span class="cite-bracket">[</span>71<span class="cite-bracket">]</span></a></sup> </p><p>Between 250,000 and 500,000 children in developing countries become blind each year owing to vitamin A deficiency.<sup id="cite_ref-ods_3-2" class="reference"><a href="#cite_note-ods-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Vitamin A deficiency is "the leading cause of preventable childhood blindness", according to <a href="/wiki/UNICEF" title="UNICEF">UNICEF</a>.<sup id="cite_ref-UNICEFvitaminA_10-1" class="reference"><a href="#cite_note-UNICEFvitaminA-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Akhtar2013_22-3" class="reference"><a href="#cite_note-Akhtar2013-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> It also increases the risk of death from common childhood conditions, such as <a href="/wiki/Diarrhea" title="Diarrhea">diarrhea</a>. UNICEF regards addressing vitamin A deficiency as critical to reducing <a href="/wiki/Child_mortality" title="Child mortality">child mortality</a>, the fourth of the <a href="/wiki/United_Nations" title="United Nations">United Nations</a>' <a href="/wiki/Millennium_Development_Goals" title="Millennium Development Goals">Millennium Development Goals</a>.<sup id="cite_ref-UNICEFvitaminA_10-2" class="reference"><a href="#cite_note-UNICEFvitaminA-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>During diagnosis, night blindness and <a href="/wiki/Xerophthalmia" title="Xerophthalmia">dry eyes</a> are signs of vitamin A deficiency that can be recognized without requiring biochemical tests. Plasma retinol is used to confirm vitamin A status. A plasma concentration of about 2.0 μmol/L is normal; less than 0.70 μmol/L (equivalent to 20 μg/dL) indicates moderate vitamin A deficiency, and less than 0.35 μmol/L (10 μg/dL) indicates severe vitamin A deficiency. Breast milk retinol of less than 8 μg/gram <a href="/wiki/Milk_fat" class="mw-redirect" title="Milk fat">milk fat</a> is considered insufficient.<sup id="cite_ref-PKIN2020VitA_6-14" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> One weakness of these measures is that they are not good indicators of liver vitamin A stores as retinyl esters in <a href="/wiki/Hepatic_stellate_cell" title="Hepatic stellate cell">hepatic stellate cells</a>. The amount of vitamin A leaving the liver, bound to retinol binding protein (RBP), is under tight control as long as there are sufficient liver reserves. Only when liver content of vitamin A drops below approximately 20 μg/gram will concentration in the blood decline.<sup id="cite_ref-DRI_VitA_5-15" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Tanumihardjo_72-0" class="reference"><a href="#cite_note-Tanumihardjo-72"><span class="cite-bracket">[</span>72<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Secondary_causes">Secondary causes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=27" title="Edit section: Secondary causes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are causes for deficiency other than low dietary intake of vitamin A as retinol or carotenes. Adequate dietary protein and caloric energy are needed for a normal rate of synthesis of RBP, without which, retinol cannot be mobilized to leave the liver. Systemic infections can cause transient decreases in RBP synthesis even if protein-calorie malnutrition is absent. Chronic alcohol consumption reduces liver vitamin A storage.<sup id="cite_ref-DRI_VitA_5-16" class="reference"><a href="#cite_note-DRI_VitA-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Non-alcoholic_fatty_liver_disease" class="mw-redirect" title="Non-alcoholic fatty liver disease">Non-alcoholic fatty liver disease</a> (NAFLD), characterized by the accumulation of fat in the liver, is the hepatic manifestation of <a href="/wiki/Metabolic_syndrome" title="Metabolic syndrome">metabolic syndrome</a>. Liver damage from NAFLD reduces liver storage capacity for retinol and reduces the ability to mobilize liver stores to maintain normal circulating concentration.<sup id="cite_ref-Saeed2017_73-0" class="reference"><a href="#cite_note-Saeed2017-73"><span class="cite-bracket">[</span>73<span class="cite-bracket">]</span></a></sup> Vitamin A appears to be involved in the pathogenesis of anemia by diverse biological mechanisms, such as the enhancement of growth and differentiation of erythrocyte progenitor cells, potentiation of immunity to infection , and mobilization of iron stores from tissues. </p> <div class="mw-heading mw-heading2"><h2 id="Animal_requirements">Animal requirements</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=28" title="Edit section: Animal requirements"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>All <a href="/wiki/Vertebrate" title="Vertebrate">vertebrate</a> and <a href="/wiki/Chordate" title="Chordate">chordate</a> species require vitamin A,<sup id="cite_ref-Marletaz2006_27-1" class="reference"><a href="#cite_note-Marletaz2006-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> either as dietary carotenoids or preformed retinol from consuming other animals. Deficiencies have been reported in laboratory-raised and pet dogs, cats, birds, reptiles and amphibians,<sup id="cite_ref-Hensel2010_74-0" class="reference"><a href="#cite_note-Hensel2010-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-75" class="reference"><a href="#cite_note-75"><span class="cite-bracket">[</span>75<span class="cite-bracket">]</span></a></sup> also commercially raised chickens and turkeys.<sup id="cite_ref-76" class="reference"><a href="#cite_note-76"><span class="cite-bracket">[</span>76<span class="cite-bracket">]</span></a></sup> Herbivore species such as horses, cattle and sheep can get sufficient β-carotene from green pasture to be healthy, but the content in pasture grass dry due to drought and long-stored hay can be too low, leading to vitamin A deficiency.<sup id="cite_ref-Hensel2010_74-1" class="reference"><a href="#cite_note-Hensel2010-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup> Omnivore and carnivore species, especially those toward the top of the food chain, can accrue large amounts of retinyl esters in their livers, or else excrete retinyl esters in urine as a means of dealing with surplus.<sup id="cite_ref-Green2016_16-4" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> Before the era of synthetic retinol, <a href="/wiki/Cod_liver_oil" title="Cod liver oil">cod liver oil</a>, high in vitamins A and D, was a commonly consumed dietary supplement.<sup id="cite_ref-77" class="reference"><a href="#cite_note-77"><span class="cite-bracket">[</span>77<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-78" class="reference"><a href="#cite_note-78"><span class="cite-bracket">[</span>78<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Invertebrate" title="Invertebrate">Invertebrates</a> cannot synthesize carotenoids or retinol, and thus must accrue these essential nutrients from consumption of algae, plants or animals.<sup id="cite_ref-79" class="reference"><a href="#cite_note-79"><span class="cite-bracket">[</span>79<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-80" class="reference"><a href="#cite_note-80"><span class="cite-bracket">[</span>80<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-81" class="reference"><a href="#cite_note-81"><span class="cite-bracket">[</span>81<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Medical_uses">Medical uses</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=29" title="Edit section: Medical uses"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In 2022, vitamin A was the 346th most commonly prescribed medication in the United States, with more than 50,000 prescriptions.<sup id="cite_ref-82" class="reference"><a href="#cite_note-82"><span class="cite-bracket">[</span>82<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Preventing_and_treating_vitamin_A_deficiency">Preventing and treating vitamin A deficiency</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=30" title="Edit section: Preventing and treating vitamin A deficiency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Vitamin_A_deficiency" title="Vitamin A deficiency">Vitamin A deficiency</a></div> <p>Recognition of its prevalence and consequences has led to governments and non-government organizations promoting vitamin A fortification of foods<sup id="cite_ref-FortifMap_58-3" class="reference"><a href="#cite_note-FortifMap-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup> and creating programs that administer large bolus-size oral doses of vitamin A to young children every four to six months.<sup id="cite_ref-Wirth2017_69-1" class="reference"><a href="#cite_note-Wirth2017-69"><span class="cite-bracket">[</span>69<span class="cite-bracket">]</span></a></sup> In 2008, the <a href="/wiki/World_Health_Organization" title="World Health Organization">World Health Organization</a> estimated that vitamin A supplementation over a decade in 40 countries averted 1.25 million deaths due to vitamin A deficiency.<sup id="cite_ref-83" class="reference"><a href="#cite_note-83"><span class="cite-bracket">[</span>83<span class="cite-bracket">]</span></a></sup> A Cochrane review reported that vitamin A supplementation is associated with a clinically meaningful reduction in morbidity and mortality in children ages six month to five years of age. All-cause mortality was reduced by 14%, and incidence of <a href="/wiki/Diarrhea" title="Diarrhea">diarrhea</a> by 12%.<sup id="cite_ref-Imdad2017_23-3" class="reference"><a href="#cite_note-Imdad2017-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> However, a Cochrane review by the same group concluded there was insufficient evidence to recommend blanket vitamin A supplementation for infants one to six months of age, as it did not reduce infant mortality or morbidity.<sup id="cite_ref-Imdad2016_49-1" class="reference"><a href="#cite_note-Imdad2016-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Acne">Acne</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=31" title="Edit section: Acne"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading4"><h4 id="Topical_retinoic_acid_and_retinol">Topical retinoic acid and retinol</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=32" title="Edit section: Topical retinoic acid and retinol"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size skin-invert-image" typeof="mw:File/Thumb"><a href="/wiki/File:Retinoids.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Retinoids.svg/220px-Retinoids.svg.png" decoding="async" width="220" height="327" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Retinoids.svg/330px-Retinoids.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Retinoids.svg/440px-Retinoids.svg.png 2x" data-file-width="3200" data-file-height="4750" /></a><figcaption>Retinoids: <a href="/wiki/Tretinoin" title="Tretinoin">Tretinoin</a> is <i>all-trans</i>-retinoic acid; initial tradename: Retin-A. <a href="/wiki/Isotretinoin" title="Isotretinoin">Isotretinoin</a> is 13-<i>cis</i>-retinoic acid; initial tradename: Accutane. <a href="/wiki/Etretinate" title="Etretinate">Etretinate</a> and <a href="/wiki/Acitretin" title="Acitretin">Acitretin</a>, its non-esterified metabolite, are used orally to treat severe <a href="/wiki/Psoriasis" title="Psoriasis">psoriasis</a>.<sup id="cite_ref-Becken2015_13-1" class="reference"><a href="#cite_note-Becken2015-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup></figcaption></figure> <p>Retinoic acids <a href="/wiki/Tretinoin" title="Tretinoin">tretinoin</a> (<i>all-trans</i>-retinoic acid) and <a href="/wiki/Isotretinoin" title="Isotretinoin">isotretinoin</a> (13-<i>cis</i>-retinoic acid) are prescription <a href="/wiki/Topical_medication" title="Topical medication">topical medications</a> used to treat moderate to severe cystic acne and acne not responsive to other treatments.<sup id="cite_ref-84" class="reference"><a href="#cite_note-84"><span class="cite-bracket">[</span>84<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-85" class="reference"><a href="#cite_note-85"><span class="cite-bracket">[</span>85<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-86" class="reference"><a href="#cite_note-86"><span class="cite-bracket">[</span>86<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Leyden2017_87-0" class="reference"><a href="#cite_note-Leyden2017-87"><span class="cite-bracket">[</span>87<span class="cite-bracket">]</span></a></sup> These are usually applied as a <a href="/wiki/Cream_(pharmacy)" title="Cream (pharmacy)">skin cream</a> to the face after cleansing to remove make-up and skin oils. Tretinoin and isotretinoin act by binding to two nuclear receptor families within keratinocytes: the retinoic acid receptors (RAR) and the retinoid X receptors (RXR).<sup id="cite_ref-Kang_S_2008_88-0" class="reference"><a href="#cite_note-Kang_S_2008-88"><span class="cite-bracket">[</span>88<span class="cite-bracket">]</span></a></sup> These events contribute to the normalization of follicular keratinization and decreased cohesiveness of keratinocytes, resulting in reduced follicular occlusion and microcomedone formation.<sup id="cite_ref-89" class="reference"><a href="#cite_note-89"><span class="cite-bracket">[</span>89<span class="cite-bracket">]</span></a></sup> The retinoid-receptor complex competes for coactivator proteins of AP-1, a key transcription factor involved in inflammation.<sup id="cite_ref-Kang_S_2008_88-1" class="reference"><a href="#cite_note-Kang_S_2008-88"><span class="cite-bracket">[</span>88<span class="cite-bracket">]</span></a></sup> Retinoic acid products also reduce <a href="/wiki/Sebum" class="mw-redirect" title="Sebum">sebum</a> secretion, a nutrient source for bacteria, from facial pores.<sup id="cite_ref-90" class="reference"><a href="#cite_note-90"><span class="cite-bracket">[</span>90<span class="cite-bracket">]</span></a></sup> </p><p>These drugs, when applied topically, are US-designated Pregnancy Category C (animal reproduction studies have shown an adverse effect on the fetus), and should not be used by pregnant women or women who are anticipating becoming pregnant.<sup id="cite_ref-Tretinoin_32-1" class="reference"><a href="#cite_note-Tretinoin-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> Many countries established a physician- and patient- education pregnancy prevention policy.<sup id="cite_ref-91" class="reference"><a href="#cite_note-91"><span class="cite-bracket">[</span>91<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Trifarotene" title="Trifarotene">Trifarotene</a> is a prescription retinoid for the topical treatment acne vulgaris.<sup id="cite_ref-Monograph_14-1" class="reference"><a href="#cite_note-Monograph-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> It functions as a <a href="/wiki/Retinoic_acid_receptor_gamma" title="Retinoic acid receptor gamma">retinoic acid receptor (RAR)-γ</a> <a href="/wiki/Agonist" title="Agonist">agonist</a>.<sup id="cite_ref-Scott2019_92-0" class="reference"><a href="#cite_note-Scott2019-92"><span class="cite-bracket">[</span>92<span class="cite-bracket">]</span></a></sup> </p><p>Non-prescription <a href="/wiki/Cream_(pharmacy)" title="Cream (pharmacy)">topical products</a> that have health claims for reducing facial acne, combating skin dark spots and reducing wrinkles and lines associated with aging often contain <a href="/wiki/Retinyl_palmitate" title="Retinyl palmitate">retinyl palmitate</a>. The hypothesis is that this is absorbed and de-esterified to free retinol, then converted to retinaldehyde and further metabolized to <i>all-trans</i>-retinoic acid, whence it will have the same effects as prescription products with fewer side effects.<sup id="cite_ref-93" class="reference"><a href="#cite_note-93"><span class="cite-bracket">[</span>93<span class="cite-bracket">]</span></a></sup> There is some <i>ex vivo</i> evidence with human skin that esterified retinol is absorbed and then converted to retinol.<sup id="cite_ref-94" class="reference"><a href="#cite_note-94"><span class="cite-bracket">[</span>94<span class="cite-bracket">]</span></a></sup> In addition to esterified retinol, some of these products contain hydroxypinacolone retinoate, identified as esterified 9-<i>cis</i>-retinoic acid.<sup id="cite_ref-95" class="reference"><a href="#cite_note-95"><span class="cite-bracket">[</span>95<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Oral_isotretinoin">Oral isotretinoin</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=33" title="Edit section: Oral isotretinoin"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Oral <a href="/wiki/Isotretinoin" title="Isotretinoin">isotretinoin</a> (retinoic acid <a href="/wiki/Isomer" title="Isomer">isomer</a>) is recommended for treating treatment resistant <a href="/wiki/Acne" title="Acne">acne</a>, acne that can lead to scarring, and acne that is associated with psychosocial distress.<sup id="cite_ref-Reynolds_2024_96-0" class="reference"><a href="#cite_note-Reynolds_2024-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> It is approved by the FDA for treating severe acne vulgaris that is resistant to other treatment options.<sup id="cite_ref-Reynolds_2024_96-1" class="reference"><a href="#cite_note-Reynolds_2024-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> Isotretinoin is a known teratogen, with an estimated 20–35% risk of physical birth defects to infants that are exposed to isotretinoin <i>in utero</i>, including numerous congenital defects such as craniofacial defects, cardiovascular and neurological malformations or thymic disorders.<sup id="cite_ref-Draghici2021_31-1" class="reference"><a href="#cite_note-Draghici2021-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> Neurocognitive impairments in the absence of any physical defects has been established to be 30–60%.<sup id="cite_ref-Draghici2021_31-2" class="reference"><a href="#cite_note-Draghici2021-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> For these reasons, physician- and patient-education programs were initiated, recommending that for women of child-bearing age, contraception be initiated a month before starting oral (or topical) isotretinoin, and continue for a month after treatment ended.<sup id="cite_ref-Draghici2021_31-3" class="reference"><a href="#cite_note-Draghici2021-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> In the US, isotretinoin was released to the market in 1982 as a revolutionary treatment for severe and refractory <a href="/wiki/Acne_vulgaris" class="mw-redirect" title="Acne vulgaris">acne vulgaris</a>. It was shown that a dose of 0.5–1.0 mg/kg body weight/day is enough to produce a reduction in sebum excretion by 90% within a month or two, but the recommended treatment duration is 4 to 6 months.<sup id="cite_ref-Draghici2021_31-4" class="reference"><a href="#cite_note-Draghici2021-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> </p><p>The mechanism by which orally consumed retinoic acid (RA), as <i>all-trans</i>-tretinoin or 13-<i>cis</i>-isotretinoin improves facial skin health is thought to be by switching on genes and differentiating keratinocytes (immature skin cells) into mature epidermal cells.<sup id="cite_ref-Reynolds_2024_96-2" class="reference"><a href="#cite_note-Reynolds_2024-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> RA reduces the size and secretion of the sebaceous glands, and by doing so reduces bacterial numbers in both the ducts and skin surface.<sup id="cite_ref-Reynolds_2024_96-3" class="reference"><a href="#cite_note-Reynolds_2024-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> It reduces inflammation via inhibition of chemotactic responses of monocytes and neutrophils. </p> <div class="mw-heading mw-heading3"><h3 id="Other_dermatological_conditions">Other dermatological conditions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=34" title="Edit section: Other dermatological conditions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In addition to the approved use for treating acne vulgaris, researchers have investigated off-label applications for dermatological conditions, such as rosacea, psoriasis, and other conditions.<sup id="cite_ref-Nickle2014_97-0" class="reference"><a href="#cite_note-Nickle2014-97"><span class="cite-bracket">[</span>97<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Rosacea" title="Rosacea">Rosacea</a> was reported as responding favorably to doses lower than used for acne. Isotretinoin in combination with ultraviolet light was shown affective for treating <a href="/wiki/Psoriasis" title="Psoriasis">psoriasis</a>. Isotretinoin in combination with injected <a href="/wiki/Interferon-alpha" class="mw-redirect" title="Interferon-alpha">interferon-alpha</a> showed some potential for treating <a href="/wiki/Genital_warts" class="mw-redirect" title="Genital warts">genital warts</a>. Isotretinoin in combination with topical <a href="/wiki/Fluorouracil" title="Fluorouracil">fluorouracil</a> or injected interferon-alpha showed some potential for treating precancerous skin lesions and skin cancer.<sup id="cite_ref-Nickle2014_97-1" class="reference"><a href="#cite_note-Nickle2014-97"><span class="cite-bracket">[</span>97<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Immune_function">Immune function</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=35" title="Edit section: Immune function"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Vitamin A plays an important role in the body's immune function, both the adaptive response, and to help the body fight off infection.<sup id="cite_ref-Cheng_2024_98-0" class="reference"><a href="#cite_note-Cheng_2024-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> The anti-inflammatory effects of vitamin A also contribute to repairing mucosal cells that can be damaged by an infection.<sup id="cite_ref-Cheng_2024_98-1" class="reference"><a href="#cite_note-Cheng_2024-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> For these reasons, there have been quite a few studies looking at the potential role that Vitamin A supplementation may play in improving an immune response or to helping the body fight off an infection. The evidence supporting vitamin A supplementation for children under the age of 7 years to prevent upper respiratory tract infections is weak, and the weak evidence from low-quality clinical trials does not support vitamin A as being effective or having a benefit.<sup id="cite_ref-Cheng_2024_98-2" class="reference"><a href="#cite_note-Cheng_2024-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> More research is needed to consider different doses, the ages and populations of people who may potentially benefit, and the length of treatment.<sup id="cite_ref-Cheng_2024_98-3" class="reference"><a href="#cite_note-Cheng_2024-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Synthesis">Synthesis</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=36" title="Edit section: Synthesis"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Biosynthesis">Biosynthesis</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=37" title="Edit section: Biosynthesis"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Carotenoid synthesis takes place in plants, certain fungi, and bacteria. Structurally carotenes are <a href="/wiki/Tetraterpene" title="Tetraterpene">tetraterpenes</a>, meaning that they are synthesized biochemically from four 10-carbon <a href="/wiki/Terpene" title="Terpene">terpene</a> units, which in turn were formed from eight 5-carbon <a href="/wiki/Isoprene" title="Isoprene">isoprene</a> units. Intermediate steps are the creation of a 40-carbon <a href="/wiki/Phytoene" title="Phytoene">phytoene</a> molecule, conversion to <a href="/wiki/Lycopene" title="Lycopene">lycopene</a> via desaturation, and then creation of ionone rings at both ends of the molecule. β-carotene has a β-ionone ring at both ends, meaning that the molecule can be divided symmetrically to yield two retinol molecules. α-Carotene has a β-ionone ring at one end and an Ɛ-ionone ring at the other, so it has half the retinol conversion capacity.<sup id="cite_ref-PKIN2020Carotenoids_12-7" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size skin-invert-image" typeof="mw:File/Thumb"><a href="/wiki/File:Chem_157_vitamin_a_synthesis_project.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Chem_157_vitamin_a_synthesis_project.png/220px-Chem_157_vitamin_a_synthesis_project.png" decoding="async" width="220" height="253" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Chem_157_vitamin_a_synthesis_project.png/330px-Chem_157_vitamin_a_synthesis_project.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Chem_157_vitamin_a_synthesis_project.png/440px-Chem_157_vitamin_a_synthesis_project.png 2x" data-file-width="1850" data-file-height="2124" /></a><figcaption>Vitamin A biosynthesis from β-carotene</figcaption></figure> <p>In most animal species, retinol is synthesized from the breakdown of the plant-formed provitamin, β-carotene. First, the enzyme <a href="/wiki/Beta-carotene_15,15%27-dioxygenase" title="Beta-carotene 15,15'-dioxygenase">beta-carotene 15,15'-dioxygenase</a> (BCO-1) cleaves β-carotene at the central double bond, creating an epoxide. This epoxide is then attacked by water creating two hydroxyl groups in the center of the structure. The cleavage occurs when these alcohols are oxidized to the aldehydes using NAD<sup>+</sup>. The resultant retinal is then quickly reduced to retinol by the enzyme retinol dehydrogenase.<sup id="cite_ref-PKIN2020VitA_6-15" class="reference"><a href="#cite_note-PKIN2020VitA-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Omnivore species such as <a href="/wiki/Canidae" title="Canidae">dogs, wolves, coyotes and foxes</a> in general are low producers of BCO-1. The enzyme is lacking in <a href="/wiki/Felidae" title="Felidae">felids</a> (cats), meaning that vitamin A requirements are met from the retinyl ester content of prey animals.<sup id="cite_ref-Green2016_16-5" class="reference"><a href="#cite_note-Green2016-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Industrial_synthesis">Industrial synthesis</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=38" title="Edit section: Industrial synthesis"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size mw-halign-left skin-invert-image" typeof="mw:File/Thumb"><a href="/wiki/File:Ionone_beta.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Ionone_beta.svg/220px-Ionone_beta.svg.png" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Ionone_beta.svg/330px-Ionone_beta.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Ionone_beta.svg/440px-Ionone_beta.svg.png 2x" data-file-width="854" data-file-height="570" /></a><figcaption>β-ionone ring</figcaption></figure> <p>β-carotene can be extracted from fungus <i>Blakeslea trispora</i>, marine algae <i>Dunaliella salina</i> or genetically modified yeast <i>Saccharomyces cerevisiae</i>, starting with xylose as a substrate.<sup id="cite_ref-Sun2020_99-0" class="reference"><a href="#cite_note-Sun2020-99"><span class="cite-bracket">[</span>99<span class="cite-bracket">]</span></a></sup> Chemical synthesis uses either a method developed by <a href="/wiki/BASF" title="BASF">BASF</a><sup id="cite_ref-β-Carotin-1_100-0" class="reference"><a href="#cite_note-β-Carotin-1-100"><span class="cite-bracket">[</span>100<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-β-Carotin-2_101-0" class="reference"><a href="#cite_note-β-Carotin-2-101"><span class="cite-bracket">[</span>101<span class="cite-bracket">]</span></a></sup> or a <a href="/wiki/Grignard_reaction" title="Grignard reaction">Grignard reaction</a> utilized by <a href="/wiki/Hoffman-La_Roche" class="mw-redirect" title="Hoffman-La Roche">Hoffman-La Roche</a>.<sup id="cite_ref-102" class="reference"><a href="#cite_note-102"><span class="cite-bracket">[</span>102<span class="cite-bracket">]</span></a></sup> </p><p>The world market for synthetic retinol is primarily for animal feed, leaving approximately 13% for a combination of food, prescription medication and dietary supplement use.<sup id="cite_ref-Parker2016_103-0" class="reference"><a href="#cite_note-Parker2016-103"><span class="cite-bracket">[</span>103<span class="cite-bracket">]</span></a></sup> Industrial methods for the production of retinol rely on chemical synthesis. The first industrialized synthesis of retinol was achieved by the company Hoffmann-La Roche in 1947. In the following decades, eight other companies developed their own processes. β-ionone, synthesized from acetone, is the essential starting point for all industrial syntheses. Each process involves elongating the unsaturated carbon chain.<sup id="cite_ref-Parker2016_103-1" class="reference"><a href="#cite_note-Parker2016-103"><span class="cite-bracket">[</span>103<span class="cite-bracket">]</span></a></sup> Pure retinol is extremely sensitive to oxidization and is prepared and transported at low temperatures and oxygen-free atmospheres. When prepared as a dietary supplement or food additive, retinol is stabilized as the ester derivatives <a href="/wiki/Retinyl_acetate" title="Retinyl acetate">retinyl acetate</a> or <a href="/wiki/Retinyl_palmitate" title="Retinyl palmitate">retinyl palmitate</a>. Prior to 1999, three companies, Roche, <a href="/wiki/BASF" title="BASF">BASF</a> and <a href="/wiki/Rhone-Poulenc" class="mw-redirect" title="Rhone-Poulenc">Rhone-Poulenc</a> controlled 96% of global vitamin A sales. In 2001, the European Commission imposed total fines of 855.22 million <a href="/wiki/Euro" title="Euro">euros</a> on these and five other companies for their participation in eight distinct market-sharing and price-fixing cartels that dated back to 1989.<sup id="cite_ref-104" class="reference"><a href="#cite_note-104"><span class="cite-bracket">[</span>104<span class="cite-bracket">]</span></a></sup> Roche sold its vitamin division to <a href="/wiki/DSM_(company)" title="DSM (company)">DSM</a> in 2003. DSM and BASF have the major share of industrial production.<sup id="cite_ref-Parker2016_103-2" class="reference"><a href="#cite_note-Parker2016-103"><span class="cite-bracket">[</span>103<span class="cite-bracket">]</span></a></sup> A biosynthesis alternative utilizes genetically engineered yeast species <i>Saccharomyces cerevisiae</i> to synthesize retinal and retinol, using xylose as a starting substrate. This was accomplished by having the yeast first synthesize β-carotene and then the cleaving enzyme β-carotene 15,15'-dioxygenase to yield retinal.<sup id="cite_ref-Sun2019_105-0" class="reference"><a href="#cite_note-Sun2019-105"><span class="cite-bracket">[</span>105<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Research">Research</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=39" title="Edit section: Research"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Brain">Brain</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=40" title="Edit section: Brain"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Animal research (on mice), which is pre-clinical, also found Retinoid acid, the bioactive metabolite of vitamin A, to have an effect on brain areas responsible for memory and learning.<sup id="cite_ref-106" class="reference"><a href="#cite_note-106"><span class="cite-bracket">[</span>106<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Cancer">Cancer</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=41" title="Edit section: Cancer"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Meta-analyses of intervention and observational trials for various types of cancer report mixed results. Supplementation with β-carotene did not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally.<sup id="cite_ref-Druesne2010_107-0" class="reference"><a href="#cite_note-Druesne2010-107"><span class="cite-bracket">[</span>107<span class="cite-bracket">]</span></a></sup> High-dose β-carotene supplementation unexpectedly resulted in a higher incidence of lung cancer and of total mortality in people who were cigarette smokers.<sup id="cite_ref-PKIN2020Carotenoids_12-8" class="reference"><a href="#cite_note-PKIN2020Carotenoids-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>For dietary retinol, no effects were observed for high dietary intake and <a href="/wiki/Breast_cancer" title="Breast cancer">breast cancer</a> survival,<sup id="cite_ref-108" class="reference"><a href="#cite_note-108"><span class="cite-bracket">[</span>108<span class="cite-bracket">]</span></a></sup> risk of <a href="/wiki/Liver_cancer" title="Liver cancer">liver cancer</a>,<sup id="cite_ref-109" class="reference"><a href="#cite_note-109"><span class="cite-bracket">[</span>109<span class="cite-bracket">]</span></a></sup> risk of <a href="/wiki/Bladder_cancer" title="Bladder cancer">bladder cancer</a><sup id="cite_ref-110" class="reference"><a href="#cite_note-110"><span class="cite-bracket">[</span>110<span class="cite-bracket">]</span></a></sup> or risk of <a href="/wiki/Colorectal_cancer" title="Colorectal cancer">colorectal cancer</a>,<sup id="cite_ref-111" class="reference"><a href="#cite_note-111"><span class="cite-bracket">[</span>111<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Xu2013_112-0" class="reference"><a href="#cite_note-Xu2013-112"><span class="cite-bracket">[</span>112<span class="cite-bracket">]</span></a></sup> although the last review did report lower risk for higher β-carotene consumption.<sup id="cite_ref-Xu2013_112-1" class="reference"><a href="#cite_note-Xu2013-112"><span class="cite-bracket">[</span>112<span class="cite-bracket">]</span></a></sup> In contrast, an inverse association was reported between retinol intake and relative risk of <a href="/wiki/Esophageal_cancer" title="Esophageal cancer">esophageal cancer</a>,<sup id="cite_ref-113" class="reference"><a href="#cite_note-113"><span class="cite-bracket">[</span>113<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Gastric_cancer" class="mw-redirect" title="Gastric cancer">gastric cancer</a>,<sup id="cite_ref-114" class="reference"><a href="#cite_note-114"><span class="cite-bracket">[</span>114<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Ovarian_cancer" title="Ovarian cancer">ovarian cancer</a>,<sup id="cite_ref-115" class="reference"><a href="#cite_note-115"><span class="cite-bracket">[</span>115<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Pancreatic_cancer" title="Pancreatic cancer">pancreatic cancer</a>,<sup id="cite_ref-116" class="reference"><a href="#cite_note-116"><span class="cite-bracket">[</span>116<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Lung_cancer" title="Lung cancer">lung cancer</a>,<sup id="cite_ref-Yu2015_117-0" class="reference"><a href="#cite_note-Yu2015-117"><span class="cite-bracket">[</span>117<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Melanoma" title="Melanoma">melanoma</a>,<sup id="cite_ref-118" class="reference"><a href="#cite_note-118"><span class="cite-bracket">[</span>118<span class="cite-bracket">]</span></a></sup> and <a href="/wiki/Cervical_cancer" title="Cervical cancer">cervical cancer</a>.<sup id="cite_ref-119" class="reference"><a href="#cite_note-119"><span class="cite-bracket">[</span>119<span class="cite-bracket">]</span></a></sup> For lung cancer, an inverse association was also seen for β-carotene intake, separate from the retinol results.<sup id="cite_ref-Yu2015_117-1" class="reference"><a href="#cite_note-Yu2015-117"><span class="cite-bracket">[</span>117<span class="cite-bracket">]</span></a></sup> When high dietary intake was compared to low dietary intake, the decreases in relative risk were in the range of 15 to 20%. For gastric cancer, a meta-analysis of prevention trials reported a 29% decrease in relative risk from retinol supplementation at 1500 μg/day<sup id="cite_ref-Kong2014_120-0" class="reference"><a href="#cite_note-Kong2014-120"><span class="cite-bracket">[</span>120<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Fetal_alcohol_spectrum_disorder">Fetal alcohol spectrum disorder</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=42" title="Edit section: Fetal alcohol spectrum disorder"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Fetal_alcohol_spectrum_disorder" title="Fetal alcohol spectrum disorder">Fetal alcohol spectrum disorder</a> (FASD), formerly referred to as fetal alcohol syndrome, presents as craniofacial malformations, neurobehavioral disorders and mental disabilities, all attributed to exposing human embryos to alcohol during fetal development.<sup id="cite_ref-Fainsod2020_121-0" class="reference"><a href="#cite_note-Fainsod2020-121"><span class="cite-bracket">[</span>121<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Petrelli2019_122-0" class="reference"><a href="#cite_note-Petrelli2019-122"><span class="cite-bracket">[</span>122<span class="cite-bracket">]</span></a></sup> The risk of FASD depends on the amount consumed, the frequency of consumption, and the points in pregnancy at which the alcohol is consumed.<sup id="cite_ref-123" class="reference"><a href="#cite_note-123"><span class="cite-bracket">[</span>123<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Ethanol" title="Ethanol">Ethanol</a> is a known <a href="/wiki/Teratogen" class="mw-redirect" title="Teratogen">teratogen</a>, i.e., causes birth defects. Ethanol is metabolized by <a href="/wiki/Alcohol_dehydrogenase" title="Alcohol dehydrogenase">alcohol dehydrogenase</a> enzymes into <a href="/wiki/Acetaldehyde" title="Acetaldehyde">acetaldehyde</a>.<sup id="cite_ref-Farrés_124-0" class="reference"><a href="#cite_note-Farrés-124"><span class="cite-bracket">[</span>124<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-125" class="reference"><a href="#cite_note-125"><span class="cite-bracket">[</span>125<span class="cite-bracket">]</span></a></sup> The subsequent oxidation of acetaldehyde into acetate is performed by <a href="/wiki/Aldehyde_dehydrogenase" title="Aldehyde dehydrogenase">aldehyde dehydrogenase</a> enzymes. Given that retinoic acid (RA) regulates numerous embryonic and differentiation processes, one of the proposed mechanisms for the teratogenic effects of ethanol is a competition for the enzymes required for the biosynthesis of RA from vitamin A. Animal research demonstrates that in the embryo, the competition takes place between acetaldehyde and retinaldehyde for aldehyde dehydrogenase activity. In this model, acetaldehyde inhibits the production of retinoic acid by retinaldehyde dehydrogenase. Ethanol-induced developmental defects can be ameliorated by increasing the levels of retinol, retinaldehyde, or retinaldehyde dehydrogenase. Thus, animal research supports the reduction of retinoic acid activity as an <a href="/wiki/Etiological" class="mw-redirect" title="Etiological">etiological</a> trigger in the induction of FASD.<sup id="cite_ref-Fainsod2020_121-1" class="reference"><a href="#cite_note-Fainsod2020-121"><span class="cite-bracket">[</span>121<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Petrelli2019_122-1" class="reference"><a href="#cite_note-Petrelli2019-122"><span class="cite-bracket">[</span>122<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Shabtai2018A_30-1" class="reference"><a href="#cite_note-Shabtai2018A-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Shabtai2018B_126-0" class="reference"><a href="#cite_note-Shabtai2018B-126"><span class="cite-bracket">[</span>126<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Malaria">Malaria</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=43" title="Edit section: Malaria"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Malaria and vitamin A deficiency are both common among young children in sub-Saharan Africa. Vitamin A supplementation to children in regions where vitamin A deficiency is common has repeatedly been shown to reduce overall mortality rates, especially from measles and diarrhea.<sup id="cite_ref-Sanj2009_127-0" class="reference"><a href="#cite_note-Sanj2009-127"><span class="cite-bracket">[</span>127<span class="cite-bracket">]</span></a></sup> For malaria, clinical trial results are mixed, either showing that vitamin A treatment did not reduce the incidence of probable malarial fever, or else did not affect incidence, but did reduce slide-confirmed parasite density and reduced the number of fever episodes.<sup id="cite_ref-Sanj2009_127-1" class="reference"><a href="#cite_note-Sanj2009-127"><span class="cite-bracket">[</span>127<span class="cite-bracket">]</span></a></sup> The question was raised as to whether malaria causes vitamin A deficiency, or vitamin A deficiency contributes to the severity of malaria, or both. Researchers proposed several mechanisms by which malaria (and other infections) could contribute to vitamin A deficiency, including a fever-induced reduction in synthesis of retinal-binding protein (RBP) responsible for transporting retinol from liver to plasma and tissues, but reported finding no evidence for a transient depression or restoration of plasma RBP or retinol after a malarial infection was eliminated.<sup id="cite_ref-Sanj2009_127-2" class="reference"><a href="#cite_note-Sanj2009-127"><span class="cite-bracket">[</span>127<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="In_history">In history</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=44" title="Edit section: In history"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Frederick_Gowland_Hopkins_nobel.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/75/Frederick_Gowland_Hopkins_nobel.jpg/220px-Frederick_Gowland_Hopkins_nobel.jpg" decoding="async" width="220" height="311" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/7/75/Frederick_Gowland_Hopkins_nobel.jpg 1.5x" data-file-width="280" data-file-height="396" /></a><figcaption>Frederick Gowland Hopkins, 1929 Nobel Prize for Physiology or Medicine</figcaption></figure> <p>In 1912, <a href="/wiki/Frederick_Gowland_Hopkins" title="Frederick Gowland Hopkins">Frederick Gowland Hopkins</a> demonstrated that unknown accessory factors found in milk, other than <a href="/wiki/Carbohydrate" title="Carbohydrate">carbohydrates</a>, <a href="/wiki/Protein" title="Protein">proteins</a>, and fats were necessary for growth in rats. Hopkins received a Nobel Prize for this discovery in 1929.<sup id="cite_ref-Wolf2001_7-2" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Semba_128-0" class="reference"><a href="#cite_note-Semba-128"><span class="cite-bracket">[</span>128<span class="cite-bracket">]</span></a></sup> By 1913, one of these substances was independently discovered by <a href="/wiki/Elmer_McCollum" title="Elmer McCollum">Elmer McCollum</a> and <a href="/wiki/Marguerite_Davis" title="Marguerite Davis">Marguerite Davis</a> at the <a href="/wiki/University_of_Wisconsin%E2%80%93Madison" title="University of Wisconsin–Madison">University of Wisconsin–Madison</a>, and <a href="/wiki/Lafayette_Mendel" title="Lafayette Mendel">Lafayette Mendel</a> and <a href="/wiki/Thomas_Burr_Osborne_(chemist)" title="Thomas Burr Osborne (chemist)">Thomas Burr Osborne</a> at <a href="/wiki/Yale_University" title="Yale University">Yale University</a>. McCollum and Davis ultimately received credit because they submitted their paper three weeks before Mendel and Osborne. Both papers appeared in the same issue of the <i><a href="/wiki/Journal_of_Biological_Chemistry" title="Journal of Biological Chemistry">Journal of Biological Chemistry</a></i> in 1913.<sup id="cite_ref-129" class="reference"><a href="#cite_note-129"><span class="cite-bracket">[</span>129<span class="cite-bracket">]</span></a></sup> The "accessory factors" were termed "fat soluble" in 1918, and later "vitamin A" in 1920. In 1919, <a href="/wiki/Harry_Steenbock" title="Harry Steenbock">Harry Steenbock</a> (University of Wisconsin–Madison) proposed a relationship between yellow plant pigments (β-carotene) and vitamin A. In 1931, Swiss chemist <a href="/wiki/Paul_Karrer" title="Paul Karrer">Paul Karrer</a> described the chemical structure of vitamin A.<sup id="cite_ref-Semba_128-1" class="reference"><a href="#cite_note-Semba-128"><span class="cite-bracket">[</span>128<span class="cite-bracket">]</span></a></sup> Retinoic acid and retinol were first synthesized in 1946 and 1947 by two Dutch chemists, <a href="/wiki/David_Adriaan_van_Dorp" title="David Adriaan van Dorp">David Adriaan van Dorp</a> and Jozef Ferdinand Arens.<sup id="cite_ref-130" class="reference"><a href="#cite_note-130"><span class="cite-bracket">[</span>130<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-131" class="reference"><a href="#cite_note-131"><span class="cite-bracket">[</span>131<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:George_Wald_nobel.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/George_Wald_nobel.jpg/220px-George_Wald_nobel.jpg" decoding="async" width="220" height="311" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/7/70/George_Wald_nobel.jpg 1.5x" data-file-width="280" data-file-height="396" /></a><figcaption>George Wald, 1967 Nobel Prize for Physiology or Medicine</figcaption></figure> <p>During <a href="/wiki/World_War_II" title="World War II">World War II</a>, German bombers would attack at night to evade British defenses. In order to keep the 1939 invention of a new on-board <a href="/wiki/Radar_in_World_War_II#Aircraft_Intercept" title="Radar in World War II">Airborne Intercept Radar</a> system secret from Germany, the British Ministry of Information told newspapers an unproven claim that the nighttime defensive success of <a href="/wiki/Royal_Air_Force" title="Royal Air Force">Royal Air Force</a> pilots was due to a high dietary intake of carrots rich in β-carotene, successfully convincing many people.<sup id="cite_ref-132" class="reference"><a href="#cite_note-132"><span class="cite-bracket">[</span>132<span class="cite-bracket">]</span></a></sup> </p><p>In 1967, <a href="/wiki/George_Wald" title="George Wald">George Wald</a> shared the Nobel Prize in Physiology and Medicine for his work on chemical visual processes in the eye.<sup id="cite_ref-nobel-1967_133-0" class="reference"><a href="#cite_note-nobel-1967-133"><span class="cite-bracket">[</span>133<span class="cite-bracket">]</span></a></sup> Wald had demonstrated in 1935 that <a href="/wiki/Photoreceptor_cell" title="Photoreceptor cell">photoreceptor cells</a> in the eye contain rhodopsin, a <a href="/wiki/Chromophore" title="Chromophore">chromophore</a> composed of the protein <a href="/wiki/Opsin" title="Opsin">opsin</a> and <a href="/wiki/11-cis_retinal" class="mw-redirect" title="11-cis retinal">11-<i>cis</i>-retinal</a>. When struck by light, 11-<i>cis</i>-retinal undergoes photoisomerization to <i>all-trans</i>-retinal and via signal transduction cascade send a nerve signal to the brain. The <i>all-trans</i>-retinal is reduced to <i>all-trans</i>-retinol and travels back to the retinal pigment epithelium to be recycled to 11-<i>cis</i>-retinal and reconjugated to opsin.<sup id="cite_ref-Wolf2001_7-3" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-134" class="reference"><a href="#cite_note-134"><span class="cite-bracket">[</span>134<span class="cite-bracket">]</span></a></sup> Wald's work was the culmination of nearly 60 years of research. In 1877, <a href="/wiki/Franz_Christian_Boll" title="Franz Christian Boll">Franz Christian Boll</a> identified a light-sensitive pigment in the outer segments of <a href="/wiki/Rod_cell" title="Rod cell">rod cells</a> of the retina that faded/bleached when exposed to light, but was restored after light exposure ceased. He suggested that this substance, by a photochemical process, conveyed the impression of light to the brain.<sup id="cite_ref-Wolf2001_7-4" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> The research was taken up by <a href="/wiki/Wilhelm_K%C3%BChne" title="Wilhelm Kühne">Wilhelm Kühne</a>, who named the pigment rhodopsin, also known as "visual purple." Kühne confirmed that rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions, and that it was this chemical decomposition that stimulated nerve impulses to the brain.<sup id="cite_ref-Wolf2001_7-5" class="reference"><a href="#cite_note-Wolf2001-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Research stalled until after identification of "fat-soluble vitamin A" as a dietary substance found in milkfat but not lard, would reverse night blindness and xerophthalmia. In 1925, Fridericia and Holm demonstrated that vitamin A deficient rats were unable to regenerate rhodopsin after being moved from a light to a dark room.<sup id="cite_ref-135" class="reference"><a href="#cite_note-135"><span class="cite-bracket">[</span>135<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=45" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-AHFS2016-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-AHFS2016_1-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.drugs.com/monograph/vitamin-a.html">"Vitamin A"</a>. The American Society of Health-System Pharmacists. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20161230232204/https://www.drugs.com/monograph/vitamin-a.html">Archived</a> from the original on 30 December 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">8 December</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Vitamin+A&rft.pub=The+American+Society+of+Health-System+Pharmacists&rft_id=https%3A%2F%2Fwww.drugs.com%2Fmonograph%2Fvitamin-a.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVitamin+A" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ec825f1c-c15f-44de-ad46-8ab9c49ec21c">"Aquasol A - vitamin a palmitate injection, solution"</a>. <i>DailyMed</i>. 14 August 2020. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20240118075117/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ec825f1c-c15f-44de-ad46-8ab9c49ec21c">Archived</a> from the original on 18 January 2024<span class="reference-accessdate">. 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Retrieved <span class="nowrap">8 August</span> 2021</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Vitamin+A+Fact+Sheet+for+Health+Professionals&rft.pub=Office+of+Dietary+Supplements%2C+US+National+Institutes+of+Health&rft.date=2021-03&rft_id=https%3A%2F%2Fods.od.nih.gov%2Ffactsheets%2FVitaminA-HealthProfessional%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVitamin+A" class="Z3988"></span></span> </li> <li id="cite_note-lpi-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-lpi_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-lpi_4-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-lpi_4-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-lpi_4-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-lpi_4-4"><sup><i><b>e</b></i></sup></a> <a href="#cite_ref-lpi_4-5"><sup><i><b>f</b></i></sup></a> <a href="#cite_ref-lpi_4-6"><sup><i><b>g</b></i></sup></a> <a href="#cite_ref-lpi_4-7"><sup><i><b>h</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://lpi.oregonstate.edu/mic/vitamins/vitamin-A">"Vitamin A"</a>. Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. 1 July 2016. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20210427223156/https://lpi.oregonstate.edu/mic/vitamins/vitamin-A">Archived</a> from the original on 27 April 2021<span class="reference-accessdate">. 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title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+American+Journal+of+Clinical+Nutrition&rft.atitle=Vitamin+A+and+retinoic+acid+in+T+cell-related+immunity&rft.volume=96&rft.issue=5&rft.pages=%3Cspan+class%3D%22nowrap%22%3E1166S+-%3C%2Fspan%3E+%3Cspan+class%3D%22nowrap%22%3E1172S%3C%2Fspan%3E&rft.date=2012-11&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3471201%23id-name%3DPMC&rft_id=info%3Apmid%2F23053562&rft_id=info%3Adoi%2F10.3945%2Fajcn.112.034637&rft.aulast=Ross&rft.aufirst=AC&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3471201&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVitamin+A" class="Z3988"></span></span> </li> <li id="cite_note-Pino2010-34"><span class="mw-cite-backlink">^ <a href="#cite_ref-Pino2010_34-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Pino2010_34-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Pino2010_34-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-Pino2010_34-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPino-LagosGuoNoelle2010" class="citation journal cs1">Pino-Lagos K, Guo Y, Noelle RJ (2010). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3826167">"Retinoic acid: a key player in immunity"</a>. <i>BioFactors</i>. <b>36</b> (6): <span class="nowrap">430–</span>436. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2Fbiof.117">10.1002/biof.117</a>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3826167">3826167</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/20803520">20803520</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=BioFactors&rft.atitle=Retinoic+acid%3A+a+key+player+in+immunity&rft.volume=36&rft.issue=6&rft.pages=%3Cspan+class%3D%22nowrap%22%3E430-%3C%2Fspan%3E436&rft.date=2010&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3826167%23id-name%3DPMC&rft_id=info%3Apmid%2F20803520&rft_id=info%3Adoi%2F10.1002%2Fbiof.117&rft.aulast=Pino-Lagos&rft.aufirst=K&rft.au=Guo%2C+Y&rft.au=Noelle%2C+RJ&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3826167&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVitamin+A" class="Z3988"></span></span> </li> <li id="cite_note-Brown2015-35"><span class="mw-cite-backlink">^ <a href="#cite_ref-Brown2015_35-0"><sup><i><b>a</b></i></sup></a> <a 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class="Z3988"></span></span> </li> <li id="cite_note-Guo2015-36"><span class="mw-cite-backlink">^ <a href="#cite_ref-Guo2015_36-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Guo2015_36-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Guo2015_36-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGuoBrownOrtizNoelle2015" class="citation journal cs1">Guo Y, Brown C, Ortiz C, Noelle RJ (January 2015). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4281589">"Leukocyte homing, fate, and function are controlled by retinoic acid"</a>. <i>Physiological Reviews</i>. <b>95</b> (1): <span class="nowrap">125–</span>148. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1152%2Fphysrev.00032.2013">10.1152/physrev.00032.2013</a>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4281589">4281589</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/25540140">25540140</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Physiological+Reviews&rft.atitle=Leukocyte+homing%2C+fate%2C+and+function+are+controlled+by+retinoic+acid&rft.volume=95&rft.issue=1&rft.pages=%3Cspan+class%3D%22nowrap%22%3E125-%3C%2Fspan%3E148&rft.date=2015-01&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4281589%23id-name%3DPMC&rft_id=info%3Apmid%2F25540140&rft_id=info%3Adoi%2F10.1152%2Fphysrev.00032.2013&rft.aulast=Guo&rft.aufirst=Y&rft.au=Brown%2C+C&rft.au=Ortiz%2C+C&rft.au=Noelle%2C+RJ&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4281589&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVitamin+A" class="Z3988"></span></span> </li> <li id="cite_note-Bono2016-37"><span class="mw-cite-backlink">^ <a href="#cite_ref-Bono2016_37-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Bono2016_37-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Bono2016_37-2"><sup><i><b>c</b></i></sup></a></span> <span 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id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Vitamin_A&action=edit&section=46" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://meshb.nlm.nih.gov/record/ui?name=Vitamin+A">Vitamin A</a> at the U.S. National Library of Medicine <a href="/wiki/Medical_Subject_Headings" title="Medical Subject Headings">Medical Subject Headings</a> (MeSH)</li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20061215060250/http://www.who.int/nutrition/publications/vitamin_a_pub/en/index.html">WHO publications on Vitamin A Deficiency</a></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist 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.navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Vitamins" title="Template:Vitamins"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Vitamins" title="Template talk:Vitamins"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Vitamins" title="Special:EditPage/Template:Vitamins"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Vitamins_(A11)79" style="font-size:114%;margin:0 4em"><a href="/wiki/Vitamin" title="Vitamin">Vitamins</a> (<a href="/wiki/ATC_code_A11" title="ATC code A11">A11</a>)</div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Fat <br />soluble</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a class="mw-selflink selflink">A</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/%CE%91-Carotene" title="Α-Carotene">α-Carotene</a></li> <li><a href="/wiki/%CE%92-Carotene" title="Β-Carotene">β-Carotene</a></li> <li><a href="/wiki/Retinol" title="Retinol">Retinol</a><sup>#</sup></li> <li><a href="/wiki/Tretinoin" title="Tretinoin">Tretinoin</a><sup>#</sup></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vitamin_D" title="Vitamin D">D</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li>D<sub>2</sub> <ul><li><a href="/wiki/Ergosterol" title="Ergosterol">Ergosterol</a></li> <li><a href="/wiki/Ergocalciferol" title="Ergocalciferol">Ergocalciferol</a><sup>#</sup></li></ul></li> <li>D<sub>3</sub> <ul><li><a href="/wiki/7-Dehydrocholesterol" title="7-Dehydrocholesterol">7-Dehydrocholesterol</a></li> <li><a href="/wiki/Previtamin_D3" title="Previtamin D3">Previtamin D<sub>3</sub></a></li> <li><a href="/wiki/Cholecalciferol" title="Cholecalciferol">Cholecalciferol</a><sup>#</sup></li> <li><a href="/wiki/Calcifediol" title="Calcifediol">25-hydroxycholecalciferol</a></li> <li><a href="/wiki/Calcitriol" title="Calcitriol">Calcitriol (1,25-dihydroxycholecalciferol)</a></li> <li><a href="/wiki/Calcitroic_acid" title="Calcitroic acid">Calcitroic acid</a></li></ul></li> <li>D<sub>4</sub> <ul><li><a href="/wiki/22-Dihydroergocalciferol" title="22-Dihydroergocalciferol">Dihydroergocalciferol</a></li></ul></li> <li><a href="/wiki/Vitamin_D5" title="Vitamin D5">D<sub>5</sub></a></li> <li>D analogues <ul><li><a href="/wiki/Alfacalcidol" title="Alfacalcidol">Alfacalcidol</a></li> <li><a href="/wiki/Dihydrotachysterol" title="Dihydrotachysterol">Dihydrotachysterol</a></li> <li><a href="/wiki/Calcipotriol" title="Calcipotriol">Calcipotriol</a></li> <li><a href="/wiki/Tacalcitol" title="Tacalcitol">Tacalcitol</a></li> <li><a href="/wiki/Paricalcitol" title="Paricalcitol">Paricalcitol</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vitamin_E" title="Vitamin E">E</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Tocopherol" title="Tocopherol">Tocopherol</a> <ul><li><a href="/wiki/%CE%91-Tocopherol" title="Α-Tocopherol">Alpha</a></li> <li><a href="/wiki/%CE%92-Tocopherol" title="Β-Tocopherol">Beta</a></li> <li><a href="/wiki/%CE%93-Tocopherol" title="Γ-Tocopherol">Gamma</a></li> <li><a href="/wiki/%CE%94-Tocopherol" title="Δ-Tocopherol">Delta</a></li></ul></li> <li><a href="/wiki/Tocotrienol" title="Tocotrienol">Tocotrienol</a> <ul><li><a href="/wiki/%CE%91-Tocotrienol" title="Α-Tocotrienol">Alpha</a></li> <li><a href="/wiki/%CE%92-Tocotrienol" title="Β-Tocotrienol">Beta</a></li> <li><a href="/wiki/%CE%93-Tocotrienol" title="Γ-Tocotrienol">Gamma</a></li> <li>Delta</li></ul></li> <li><a href="/wiki/Tocofersolan" title="Tocofersolan">Tocofersolan</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vitamin_K" title="Vitamin K">K</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/1,4-Naphthoquinone" title="1,4-Naphthoquinone">Naphthoquinone</a></li> <li><a href="/wiki/Phytomenadione" title="Phytomenadione">Phylloquinone (K<sub>1</sub>)</a><sup>#</sup></li> <li><a href="/wiki/Vitamin_K2" title="Vitamin K2">Menaquinones (K<sub>2</sub>)</a></li> <li><a href="/wiki/Menadione" title="Menadione">Menadione (K<sub>3</sub>)</a><sup>‡</sup></li> <li><a href="/wiki/Vitamin_K4" class="mw-redirect" title="Vitamin K4">Various (K<sub>4</sub>)</a></li> <li><a href="/wiki/4-Amino-2-methyl-1-naphthol" title="4-Amino-2-methyl-1-naphthol">4-Amino-2-methyl-1-naphthol (K<sub>5</sub>)</a><sup>‡</sup></li> <li><a href="/wiki/2-Methylnaphthalene-1,4-diamine" title="2-Methylnaphthalene-1,4-diamine">2-Methylnaphthalene-1,4-diamine (K<sub>6</sub>)</a></li> <li><a href="/wiki/4-Amino-3-methyl-1-naphthol" title="4-Amino-3-methyl-1-naphthol">4-Amino-3-methyl-1-naphthol (K<sub>7</sub>)</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Water <br />soluble</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/B_vitamins" title="B vitamins">B</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li>B<sub>1</sub> <ul><li><a href="/wiki/Thiamine" title="Thiamine">Thiamine</a><sup>#</sup></li></ul></li> <li><a href="/wiki/Vitamin_B1_analogues" title="Vitamin B1 analogues">B<sub>1</sub> analogues</a> <ul><li><a href="/wiki/Acefurtiamine" title="Acefurtiamine">Acefurtiamine</a></li> <li><a href="/wiki/Allithiamine" title="Allithiamine">Allithiamine</a></li> <li><a href="/wiki/Benfotiamine" title="Benfotiamine">Benfotiamine</a></li> <li><a href="/wiki/Fursultiamine" title="Fursultiamine">Fursultiamine</a></li> <li><a href="/wiki/Octotiamine" title="Octotiamine">Octotiamine</a></li> <li><a href="/wiki/Prosultiamine" title="Prosultiamine">Prosultiamine</a></li> <li><a href="/wiki/Sulbutiamine" title="Sulbutiamine">Sulbutiamine</a></li></ul></li> <li>B<sub>2</sub> <ul><li><a href="/wiki/Riboflavin" title="Riboflavin">Riboflavin</a><sup>#</sup></li></ul></li> <li><a href="/wiki/Vitamin_B3" title="Vitamin B3">B<sub>3</sub></a> <ul><li><a href="/wiki/Nicotinic_acid" title="Nicotinic acid">Nicotinic acid</a></li> <li><a href="/wiki/Nicotinamide" title="Nicotinamide">Nicotinamide</a><sup>#</sup></li></ul></li> <li>B<sub>5</sub> <ul><li><a href="/wiki/Pantothenic_acid" title="Pantothenic acid">Pantothenic acid</a></li> <li><a href="/wiki/Panthenol" title="Panthenol">Dexpanthenol</a></li> <li><a href="/wiki/Pantethine" title="Pantethine">Pantethine</a></li></ul></li> <li><a href="/wiki/Vitamin_B6" title="Vitamin B6">B<sub>6</sub></a> <ul><li><a href="/wiki/Pyridoxine" title="Pyridoxine">Pyridoxine</a><sup>#</sup>, <a href="/wiki/Pyridoxal_phosphate" title="Pyridoxal phosphate">Pyridoxal phosphate</a></li> <li><a href="/wiki/Pyridoxamine" title="Pyridoxamine">Pyridoxamine</a></li> <li><a href="/wiki/Pyritinol" title="Pyritinol">Pyritinol</a></li></ul></li> <li>B<sub>7</sub> <ul><li><a href="/wiki/Biotin" title="Biotin">Biotin</a></li></ul></li> <li>B<sub>9</sub> <ul><li><a href="/wiki/Folate" title="Folate">Folic acid</a><sup>#</sup></li> <li><a href="/wiki/Dihydrofolic_acid" title="Dihydrofolic acid">Dihydrofolic acid</a></li> <li><a href="/wiki/Folinic_acid" title="Folinic acid">Folinic acid</a></li> <li><a href="/wiki/Levomefolic_acid" title="Levomefolic acid">Levomefolic acid</a></li></ul></li> <li><a href="/wiki/Vitamin_B12" title="Vitamin B12">B<sub>12</sub></a> <ul><li><a href="/wiki/Adenosylcobalamin" title="Adenosylcobalamin">Adenosylcobalamin</a></li> <li><a href="/wiki/Cyanocobalamin" title="Cyanocobalamin">Cyanocobalamin</a></li> <li><a href="/wiki/Hydroxocobalamin" title="Hydroxocobalamin">Hydroxocobalamin</a><sup>#</sup></li> <li><a href="/wiki/Methylcobalamin" title="Methylcobalamin">Methylcobalamin</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vitamin_C" title="Vitamin C">C</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Vitamin_C" title="Vitamin C">Ascorbic acid</a><sup>#</sup></li> <li><a href="/wiki/Dehydroascorbic_acid" title="Dehydroascorbic acid">Dehydroascorbic acid</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Combinations</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Multivitamin" title="Multivitamin">Multivitamins</a></li></ul> </div></td></tr><tr><td colspan="2" class="navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"><div class="hlist"> <ul><li><sup>#</sup><a href="/wiki/WHO_Model_List_of_Essential_Medicines" title="WHO Model List of Essential Medicines">WHO-EM</a></li> <li><sup>‡</sup><a href="/wiki/List_of_withdrawn_drugs" title="List of withdrawn drugs">Withdrawn</a> from market</li> <li><a href="/wiki/Clinical_trial" title="Clinical trial">Clinical trials</a>: <ul><li><sup>†</sup><a href="/wiki/Phases_of_clinical_research#Phase_III" title="Phases of clinical research">Phase III</a></li> <li><sup>§</sup>Never to phase III</li></ul></li></ul> </div></div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Antioxidants62" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Antioxidants" title="Template:Antioxidants"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Antioxidants" title="Template talk:Antioxidants"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Antioxidants" title="Special:EditPage/Template:Antioxidants"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Antioxidants62" style="font-size:114%;margin:0 4em"><a href="/wiki/Antioxidant" title="Antioxidant">Antioxidants</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Food antioxidants</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/6-Hydroxymelatonin" title="6-Hydroxymelatonin">6-Hydroxymelatonin</a></li> <li><a href="/wiki/Acetylcarnitine" title="Acetylcarnitine">Acetyl-<small>L</small>-carnitine</a> (ALCAR)</li> <li><a href="/wiki/Lipoic_acid" title="Lipoic acid">Alpha-lipoic acid</a> (ALA)</li> <li><a href="/wiki/Vitamin_C" title="Vitamin C">Ascorbic acid</a> (vitamin C)</li> <li><a href="/wiki/Carotenoid" title="Carotenoid">Carotenoids</a> (<a class="mw-selflink selflink">vitamin A</a>)</li> <li><a href="/wiki/Curcumin" title="Curcumin">Curcumin</a></li> <li><a href="/wiki/Edaravone" title="Edaravone">Edaravone</a></li> <li><a href="/wiki/Antioxidant_effect_of_polyphenols_and_natural_phenols" title="Antioxidant effect of polyphenols and natural phenols">Polyphenols</a></li> <li><a href="/wiki/Glutathione" title="Glutathione">Glutathione</a></li> <li><a href="/wiki/Hydroxytyrosol" title="Hydroxytyrosol">Hydroxytyrosol</a></li> <li><a href="/wiki/Carnitine" title="Carnitine"><small>L</small>-carnitine</a></li> <li><a href="/wiki/Ladostigil" title="Ladostigil">Ladostigil</a></li> <li><a href="/wiki/Melatonin" title="Melatonin">Melatonin</a></li> <li><a href="/wiki/Mofegiline" title="Mofegiline">Mofegiline</a></li> <li><a href="/wiki/Acetylcysteine" title="Acetylcysteine"><i>N</i>-Acetylcysteine</a> (NAC)</li> <li><a href="/wiki/N-Acetylserotonin" title="N-Acetylserotonin"><i>N</i>-Acetylserotonin</a> (NAS)</li> <li><a href="/wiki/Oleocanthal" title="Oleocanthal">Oleocanthal</a></li> <li><a href="/wiki/Oleuropein" title="Oleuropein">Oleuropein</a></li> <li><a href="/wiki/Rasagiline" title="Rasagiline">Rasagiline</a></li> <li><a href="/wiki/Resveratrol" title="Resveratrol">Resveratrol</a></li> <li><a href="/wiki/Selegiline" title="Selegiline">Selegiline</a></li> <li><a href="/wiki/Selenium" title="Selenium">Selenium</a></li> <li><a href="/wiki/Tocopherol" title="Tocopherol">Tocopherols</a> (<a href="/wiki/Vitamin_E" title="Vitamin E">vitamin E</a>)</li> <li><a href="/wiki/Tocotrienol" title="Tocotrienol">Tocotrienols</a> (<a href="/wiki/Vitamin_E" title="Vitamin E">vitamin E</a>)</li> <li><a href="/wiki/Tyrosol" title="Tyrosol">Tyrosol</a></li> <li><a href="/wiki/Coenzyme_Q10" title="Coenzyme Q10">Ubiquinone</a> (coenzyme Q)</li> <li><a href="/wiki/Uric_acid" title="Uric acid">Uric acid</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Fuel antioxidants</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Butylated_hydroxyanisole" title="Butylated hydroxyanisole">Butylated hydroxyanisole</a></li> <li><a href="/wiki/Butylated_hydroxytoluene" title="Butylated hydroxytoluene">Butylated hydroxytoluene</a></li> <li><a href="/wiki/2,6-Di-tert-butylphenol" title="2,6-Di-tert-butylphenol">2,6-Di-<i>tert</i>-butylphenol</a></li> <li><a href="/wiki/1,2-Diaminopropane" title="1,2-Diaminopropane">1,2-Diaminopropane</a></li> <li><a href="/wiki/2,4-Dimethyl-6-tert-butylphenol" title="2,4-Dimethyl-6-tert-butylphenol">2,4-Dimethyl-6-<i>tert</i>-butylphenol</a></li> <li><a href="/wiki/Ethylenediamine" title="Ethylenediamine">Ethylenediamine</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Measurements</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Folin%E2%80%93Ciocalteu_reagent" title="Folin–Ciocalteu reagent">Folin method</a></li> <li><a href="/wiki/Oxygen_radical_absorbance_capacity" title="Oxygen radical absorbance capacity">ORAC</a></li> <li><a href="/wiki/Trolox_equivalent_antioxidant_capacity" title="Trolox equivalent antioxidant capacity">TEAC</a></li> <li><a href="/wiki/Ferric_reducing_ability_of_plasma" title="Ferric reducing ability of plasma">FRAP</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link 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class="nv-edit"><a href="/wiki/Special:EditPage/Template:Dietary_supplement" title="Special:EditPage/Template:Dietary supplement"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Dietary_supplements155" style="font-size:114%;margin:0 4em"><a href="/wiki/Dietary_supplement" title="Dietary supplement">Dietary supplements</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Types</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bodybuilding_supplement" title="Bodybuilding supplement">Bodybuilding supplement</a></li> <li><a href="/wiki/Energy_drink" title="Energy drink">Energy drink</a></li> <li><a href="/wiki/Energy_bar" title="Energy bar">Energy bar</a></li> <li><a href="/wiki/Essential_fatty_acid" title="Essential fatty acid">Fatty acids</a></li> <li><a href="/wiki/Herbal_medicine" title="Herbal medicine">Herbal supplements</a></li> <li><a href="/wiki/Mineral_(nutrient)" title="Mineral (nutrient)">Minerals</a></li> <li><a href="/wiki/Prebiotic_(nutrition)" title="Prebiotic (nutrition)">Prebiotics</a></li> <li><a href="/wiki/Probiotic" title="Probiotic">Probiotics</a> (<a href="/wiki/Lactobacillus" title="Lactobacillus">Lactobacillus</a></li> <li><a href="/wiki/Bifidobacterium" title="Bifidobacterium">Bifidobacterium</a>)</li> <li><a href="/wiki/Protein_supplement" title="Protein supplement">Protein supplements</a></li> <li><a href="/wiki/Vitamin" title="Vitamin">Vitamins</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Vitamin" title="Vitamin">Vitamins</a> and<br /><a href="/wiki/Mineral_(nutrient)" title="Mineral (nutrient)">chemical elements<br /> ("minerals")</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a class="mw-selflink selflink">Retinol (Vitamin A)</a></li> <li><a href="/wiki/B_vitamins" title="B vitamins">B vitamins</a> <ul><li><a href="/wiki/Thiamine" title="Thiamine">Thiamine (B<sub>1</sub>)</a></li> <li><a href="/wiki/Riboflavin" title="Riboflavin">Riboflavin (B<sub>2</sub>)</a></li> <li><a href="/wiki/Niacin_(nutrient)" class="mw-redirect" title="Niacin (nutrient)">Niacin (B<sub>3</sub>)</a></li> <li><a href="/wiki/Pantothenic_acid" title="Pantothenic acid">Pantothenic acid (B<sub>5</sub>)</a></li> <li><a href="/wiki/Vitamin_B6" title="Vitamin B6">Pyridoxine (B<sub>6</sub>)</a></li> <li><a href="/wiki/Biotin" title="Biotin">Biotin (B<sub>7</sub>)</a></li> <li><a href="/wiki/Folate" title="Folate">Folic acid (B<sub>9</sub>)</a></li> <li><a href="/wiki/Cyanocobalamin" title="Cyanocobalamin">Cyanocobalamin (B<sub>12</sub>)</a></li></ul></li> <li><a href="/wiki/Vitamin_C" title="Vitamin C">Ascorbic acid (Vitamin C)</a></li> <li><a href="/wiki/Vitamin_D" title="Vitamin D">Ergocalciferol and Cholecalciferol (Vitamin D)</a></li> <li><a href="/wiki/Vitamin_E" title="Vitamin E">Tocopherol (Vitamin E)</a></li> <li><a href="/wiki/Vitamin_K" title="Vitamin K">Naphthoquinone (Vitamin K)</a></li></ul> <ul><li><a href="/wiki/Calcium_supplement" title="Calcium supplement">Calcium</a></li> <li><a href="/wiki/Choline" title="Choline">Choline</a></li> <li><a href="/wiki/Chromium" title="Chromium">Chromium</a></li> <li><a href="/wiki/Cobalt" title="Cobalt">Cobalt</a></li> <li><a href="/wiki/Copper" title="Copper">Copper</a></li> <li><a href="/wiki/Fluorine" title="Fluorine">Fluorine</a></li> <li><a href="/wiki/Iodine" title="Iodine">Iodine</a></li> <li><a href="/wiki/Iron" title="Iron">Iron</a></li> <li><a href="/wiki/Magnesium" title="Magnesium">Magnesium</a></li> <li><a href="/wiki/Manganese" title="Manganese">Manganese</a></li> <li><a href="/wiki/Molybdenum" title="Molybdenum">Molybdenum</a></li> <li><a href="/wiki/Phosphorus" title="Phosphorus">Phosphorus</a></li> <li><a href="/wiki/Potassium" title="Potassium">Potassium</a></li> <li><a href="/wiki/Selenium" title="Selenium">Selenium</a></li> <li><a href="/wiki/Sodium" title="Sodium">Sodium</a></li> <li><a href="/wiki/Sulfur" title="Sulfur">Sulfur</a></li> <li><a href="/wiki/Zinc" title="Zinc">Zinc</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other common <br />ingredients</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Arginine_alpha-ketoglutarate" title="Arginine alpha-ketoglutarate">AAKG</a></li> <li><a href="/wiki/Beta-Hydroxy_beta-methylbutyric_acid" class="mw-redirect" title="Beta-Hydroxy beta-methylbutyric acid">β-hydroxy β-methylbutyrate</a></li> <li><a href="/wiki/Carnitine" title="Carnitine">Carnitine</a></li> <li><a href="/wiki/Chondroitin_sulfate" title="Chondroitin sulfate">Chondroitin sulfate</a></li> <li><a href="/wiki/Cod_liver_oil" title="Cod liver oil">Cod liver oil</a></li> <li><a href="/wiki/Copper_gluconate" title="Copper gluconate">Copper gluconate</a></li> <li><a href="/wiki/Creatine" title="Creatine">Creatine</a></li> <li><a href="/wiki/Dietary_fiber" title="Dietary fiber">Dietary fiber</a></li> <li><a href="/wiki/Echinacea#Medicinal_effects" title="Echinacea">Echinacea</a></li> <li><a href="/wiki/Ephedra_(medicine)" title="Ephedra (medicine)">Ephedra</a></li> <li><a href="/wiki/Fish_oil" title="Fish oil">Fish oil</a></li> <li><a href="/wiki/Folate" title="Folate">Folic acid</a></li> <li><a href="/wiki/Ginseng" title="Ginseng">Ginseng</a></li> <li><a href="/wiki/Glucosamine" title="Glucosamine">Glucosamine</a></li> <li><a href="/wiki/Glutamine" title="Glutamine">Glutamine</a></li> <li><a href="/wiki/Grape_seed_extract" title="Grape seed extract">Grape seed extract</a></li> <li><a href="/wiki/Guarana" title="Guarana">Guarana</a></li> <li><a href="/wiki/Iron_supplement" title="Iron supplement">Iron supplements</a></li> <li><a href="/wiki/Lonicera_japonica" title="Lonicera japonica">Japanese honeysuckle</a></li> <li><a href="/wiki/Krill_oil" title="Krill oil">Krill oil</a></li> <li><a href="/wiki/Lingzhi_(mushroom)" title="Lingzhi (mushroom)">Lingzhi</a></li> <li><a href="/wiki/Linseed_oil" title="Linseed oil">Linseed oil</a></li> <li><a href="/wiki/Lipoic_acid" title="Lipoic acid">Lipoic acid</a></li> <li><a href="/wiki/Silybum_marianum#Health_benefits" title="Silybum marianum">Milk thistle</a></li> <li><a href="/wiki/Melatonin_(supplement)" class="mw-redirect" title="Melatonin (supplement)">Melatonin</a></li> <li><a href="/wiki/Red_yeast_rice" title="Red yeast rice">Red yeast rice</a></li> <li><a href="/wiki/Royal_jelly" title="Royal jelly">Royal jelly</a></li> <li><a href="/wiki/Saw_palmetto_extract" title="Saw palmetto extract">Saw palmetto</a></li> <li><a href="/wiki/Spirulina_(dietary_supplement)" title="Spirulina (dietary supplement)">Spirulina</a></li> <li><a href="/wiki/Hypericum_perforatum#Medicinal_uses" title="Hypericum perforatum">St John's wort</a></li> <li><a href="/wiki/Taurine" title="Taurine">Taurine</a></li> <li><a href="/wiki/Wheatgrass" title="Wheatgrass">Wheatgrass</a></li> <li><a href="/wiki/Goji" title="Goji">Wolfberry</a></li> <li><a href="/wiki/Yohimbine" title="Yohimbine">Yohimbine</a></li> <li><a href="/wiki/Zinc_gluconate" title="Zinc gluconate">Zinc gluconate</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related articles</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Codex_Alimentarius" title="Codex Alimentarius">Codex Alimentarius</a></li> <li><a href="/wiki/Enzyte" title="Enzyte">Enzyte</a></li> <li><a href="/wiki/Hadacol" title="Hadacol">Hadacol</a></li> <li><a href="/wiki/Herbal_tea" title="Herbal tea">Herbal tea</a></li> <li><a href="/wiki/Nutraceutical" title="Nutraceutical">Nutraceutical</a></li> <li><a href="/wiki/Multivitamin" title="Multivitamin">Multivitamin</a></li> <li><a href="/wiki/Nutrition" title="Nutrition">Nutrition</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Retinoid_receptor_modulators924" style="padding:3px"><table class="nowraplinks hlist mw-collapsible mw-collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Retinoid_receptor_modulators" title="Template:Retinoid receptor modulators"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Retinoid_receptor_modulators" title="Template talk:Retinoid receptor modulators"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Retinoid_receptor_modulators" title="Special:EditPage/Template:Retinoid receptor modulators"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Retinoid_receptor_modulators924" style="font-size:114%;margin:0 4em"><a href="/wiki/Retinoid_receptor" title="Retinoid receptor">Retinoid receptor</a> <a href="/wiki/Receptor_modulator" title="Receptor modulator">modulators</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:center;"><a href="/wiki/Retinoic_acid_receptor" title="Retinoic acid receptor"><abbr title="Retinoic acid receptor">RAR</abbr></a><span class="sr-only" style="border: 0; clip: rect(0, 0, 0, 0); clip-path: polygon(0px 0px, 0px 0px, 0px 0px); height: 1px; margin: -1px; overflow: hidden; padding: 0; position: absolute; width: 1px; white-space: nowrap;">Tooltip Retinoic acid receptor</span></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i>Agonists:</i> <a href="/w/index.php?title=9-cis-13,14-Dihydro-retinoic_acid&action=edit&redlink=1" class="new" title="9-cis-13,14-Dihydro-retinoic acid (page does not exist)">9CDHRA</a></li> <li><a href="/wiki/Alitretinoin" title="Alitretinoin">9-<i>cis</i>-Retinoic acid (alitretinoin)</a></li> <li><a href="/w/index.php?title=AC-261066&action=edit&redlink=1" class="new" title="AC-261066 (page does not exist)">AC-261066</a></li> <li><a href="/w/index.php?title=AC-55649&action=edit&redlink=1" class="new" title="AC-55649 (page does not exist)">AC-55649</a></li> <li><a href="/wiki/Acitretin" title="Acitretin">Acitretin</a></li> <li><a href="/wiki/Adapalene" title="Adapalene">Adapalene</a></li> <li><a href="/wiki/Tretinoin" title="Tretinoin">all-<i>trans</i>-Retinoic acid (tretinoin)</a></li> <li><a href="/w/index.php?title=AM-580&action=edit&redlink=1" class="new" title="AM-580 (page does not exist)">AM-580</a></li> <li><a href="/w/index.php?title=BMS-493&action=edit&redlink=1" class="new" title="BMS-493 (page does not exist)">BMS-493</a></li> <li><a href="/w/index.php?title=BMS-753&action=edit&redlink=1" class="new" title="BMS-753 (page does not exist)">BMS-753</a></li> <li><a href="/w/index.php?title=BMS-961&action=edit&redlink=1" class="new" title="BMS-961 (page does not exist)">BMS-961</a></li> <li><a href="/w/index.php?title=CD-1530&action=edit&redlink=1" class="new" title="CD-1530 (page does not exist)">CD-1530</a></li> <li><a href="/w/index.php?title=CD-2314&action=edit&redlink=1" class="new" title="CD-2314 (page does not exist)">CD-2314</a></li> <li><a href="/w/index.php?title=CD-437&action=edit&redlink=1" class="new" title="CD-437 (page does not exist)">CD-437</a></li> <li><a href="/w/index.php?title=Ch-55&action=edit&redlink=1" class="new" title="Ch-55 (page does not exist)">Ch-55</a></li> <li><a href="/w/index.php?title=EC_23&action=edit&redlink=1" class="new" title="EC 23 (page does not exist)">EC 23</a></li> <li><a href="/wiki/Etretinate" title="Etretinate">Etretinate</a></li> <li><a href="/wiki/Fenretinide" title="Fenretinide">Fenretinide</a></li> <li><a href="/wiki/Isotretinoin" title="Isotretinoin">Isotretinoin</a></li> <li><a href="/wiki/Palovarotene" title="Palovarotene">Palovarotene</a></li> <li><a href="/wiki/Retinoic_acid" title="Retinoic acid">Retinoic acid</a></li> <li><a href="/wiki/Retinol" title="Retinol">Retinol</a> (<a class="mw-selflink selflink">vitamin A</a>)</li> <li><a href="/wiki/Tamibarotene" title="Tamibarotene">Tamibarotene</a></li> <li><a href="/wiki/Tazarotene" title="Tazarotene">Tazarotene</a></li> <li><a href="/w/index.php?title=Tazarotenic_acid&action=edit&redlink=1" class="new" title="Tazarotenic acid (page does not exist)">Tazarotenic acid</a></li> <li><a href="/wiki/Trifarotene" title="Trifarotene">Trifarotene</a></li> <li><a href="/w/index.php?title=TTNPB&action=edit&redlink=1" class="new" title="TTNPB (page does not exist)">TTNPB</a></li></ul> <ul><li><i>Antagonists:</i> <a href="/w/index.php?title=BMS-195614&action=edit&redlink=1" class="new" title="BMS-195614 (page does not exist)">BMS-195614</a></li> <li><a href="/w/index.php?title=BMS-493&action=edit&redlink=1" class="new" title="BMS-493 (page does not exist)">BMS-493</a></li> <li><a href="/w/index.php?title=CD-2665&action=edit&redlink=1" class="new" title="CD-2665 (page does not exist)">CD-2665</a></li> <li><a href="/w/index.php?title=ER-50891&action=edit&redlink=1" class="new" title="ER-50891 (page does not exist)">ER-50891</a></li> <li><a href="/w/index.php?title=LE-135&action=edit&redlink=1" class="new" title="LE-135 (page does not exist)">LE-135</a></li> <li><a href="/w/index.php?title=MM-11253&action=edit&redlink=1" class="new" title="MM-11253 (page does not exist)">MM-11253</a></li></ul> <ul><li><i>Retinoic acid metabolism inhibitors:</i> <a href="/wiki/Liarozole" title="Liarozole">Liarozole</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:center;"><a href="/wiki/Retinoid_X_receptor" title="Retinoid X receptor"><abbr title="Retinoid X receptor">RXR</abbr></a><span class="sr-only" style="border: 0; clip: rect(0, 0, 0, 0); clip-path: polygon(0px 0px, 0px 0px, 0px 0px); height: 1px; margin: -1px; overflow: hidden; padding: 0; position: absolute; width: 1px; white-space: nowrap;">Tooltip Retinoid X receptor</span></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i>Agonists:</i> <a href="/w/index.php?title=9-cis-13,14-Dihydro-retinoic_acid&action=edit&redlink=1" class="new" title="9-cis-13,14-Dihydro-retinoic acid (page does not exist)">9CDHRA</a></li> <li><a href="/wiki/Alitretinoin" title="Alitretinoin">9-<i>cis</i>-Retinoic acid (alitretinoin)</a></li> <li><a href="/wiki/Tretinoin" title="Tretinoin">all-<i>trans</i>-Retinoic acid (tretinoin)</a></li> <li><a href="/wiki/Bexarotene" title="Bexarotene">Bexarotene</a></li> <li><a href="/w/index.php?title=CD_3254&action=edit&redlink=1" class="new" title="CD 3254 (page does not exist)">CD 3254</a></li> <li><a href="/wiki/Docosahexaenoic_acid" title="Docosahexaenoic acid">Docosahexaenoic acid</a></li> <li><a href="/w/index.php?title=Fluorobexarotene&action=edit&redlink=1" class="new" title="Fluorobexarotene (page does not exist)">Fluorobexarotene</a></li> <li><a href="/wiki/Isotretinoin" title="Isotretinoin">Isotretinoin</a></li> <li><a href="/w/index.php?title=LG-100268&action=edit&redlink=1" class="new" title="LG-100268 (page does not exist)">LG-100268</a></li> <li><a href="/w/index.php?title=LG-101506&action=edit&redlink=1" class="new" title="LG-101506 (page does not exist)">LG-101506</a></li> <li><a href="/w/index.php?title=LG-100754&action=edit&redlink=1" class="new" title="LG-100754 (page does not exist)">LG-100754</a></li> <li><a href="/wiki/Retinoic_acid" title="Retinoic acid">Retinoic acid</a></li> <li><a href="/wiki/Retinol" title="Retinol">Retinol</a> (<a class="mw-selflink selflink">vitamin A</a>)</li> <li><a href="/w/index.php?title=SR-11237&action=edit&redlink=1" class="new" title="SR-11237 (page does not exist)">SR-11237</a></li></ul> <ul><li><i>Antagonists:</i> <a href="/w/index.php?title=HX-531&action=edit&redlink=1" class="new" title="HX-531 (page does not exist)">HX-531</a></li> <li><a href="/w/index.php?title=HX-630&action=edit&redlink=1" class="new" title="HX-630 (page does not exist)">HX-630</a></li> <li><a href="/w/index.php?title=LG-100754&action=edit&redlink=1" class="new" title="LG-100754 (page does not exist)">LG-100754</a></li> <li><a href="/w/index.php?title=PA-452&action=edit&redlink=1" class="new" title="PA-452 (page does not exist)">PA-452</a></li> <li><a href="/w/index.php?title=UVI-3003&action=edit&redlink=1" class="new" title="UVI-3003 (page does not exist)">UVI-3003</a></li> <li><a href="/w/index.php?title=HX-603&action=edit&redlink=1" class="new" title="HX-603 (page does not exist)">HX-603</a></li> <li><a href="/w/index.php?title=LE135_(RAR_beta_selective)&action=edit&redlink=1" class="new" title="LE135 (RAR beta selective) (page does not exist)">LE135 (RAR beta selective)</a></li> <li><a href="/w/index.php?title=LE-540&action=edit&redlink=1" class="new" title="LE-540 (page does not exist)">LE-540</a></li> <li><a href="/w/index.php?title=CD3254&action=edit&redlink=1" class="new" title="CD3254 (page does not exist)">CD3254</a></li> <li><a href="/w/index.php?title=PA-451&action=edit&redlink=1" class="new" title="PA-451 (page does not exist)">PA-451</a></li> <li><a href="/w/index.php?title=PA-452&action=edit&redlink=1" class="new" title="PA-452 (page does not exist)">PA-452</a></li> <li><a href="/wiki/Rhein_(molecule)" title="Rhein (molecule)">Rhein</a></li> <li><a href="/w/index.php?title=HX-711&action=edit&redlink=1" class="new" title="HX-711 (page does not exist)">HX-711</a></li> <li><a href="/w/index.php?title=6-(N-ethyl-N-(5-isobutoxy-4-isopropyl-2-(E)-styrylphenyl)amino)nicotinic_acid&action=edit&redlink=1" class="new" title="6-(N-ethyl-N-(5-isobutoxy-4-isopropyl-2-(E)-styrylphenyl)amino)nicotinic acid (page does not exist)">6-(N-ethyl-N-(5-isobutoxy-4-isopropyl-2-(E)-styrylphenyl)amino)nicotinic acid</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <dl><dt>See also</dt> <dd><i><a href="/wiki/Template:Receptor_modulators" title="Template:Receptor modulators">Receptor/signaling modulators</a></i></dd></dl> </div></td></tr></tbody></table></div> <style 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