Editing Retinol (section)

==Nutrition==
{| class="wikitable" style="width:300px; float:right; margin:0 0 0 0.5em; background:#fff; border-collapse:collapse;"
|-
! style="background:#fda;" colspan="2"| Vitamin properties
|-
| style="background:#fed;"| [[Solubility]]
| Fat
|-
| style="background:#fed;"| [[Recommended Dietary Allowance|RDA]] (adult male)
| 900 [[microgram|μg]]/day
|-
| style="background:#fed;"| RDA (adult female)
| 700 [[microgram|μg]]/day
|-
| style="background:#fed;"| RDA upper limit (adult male)
| 3,000 [[microgram|μg]]/day
|-
| style="background:#fed;"| RDA upper limit (adult female)
| 3,000 [[microgram|μg]]/day
|-
! style="background:#fed;" colspan="2"| Deficiency symptoms
|-
| colspan="2" |
* [[Night blindness]]
* [[Keratomalacia]]
* Pale, dry skin
|-
! style="background:#fed;" colspan="2"| Excess symptoms
|-
| colspan="2" |
* Liver toxicity
* Dry skin
* Hair loss
* [[Teratogenesis|Teratological]] effects
* [[Osteoporosis]] (suspected, long-term)
|-
! style="background:#fda;" colspan="2"| Common sources
|-
| colspan="2" |
* [[Liver]] and other organs
* fortified [[Dairy products]]
|}
This vitamin plays an essential role in vision, particularly night vision, normal bone and tooth development, reproduction, and the health of skin and mucous membranes (the mucus-secreting layer that lines body regions such as the respiratory tract). While Vitamin A is often considered to be an antioxidant that prevents cancers, it does not have antioxidant activity<ref>{{cite journal | vauthors = Blaner WS, Shmarakov IO, Traber MG | title = Vitamin A and Vitamin E: Will the Real Antioxidant Please Stand Up? | journal = Annual Review of Nutrition | volume = 41 | pages = 105–131 | date = October 2021 | pmid = 34115520 | doi = 10.1146/annurev-nutr-082018-124228 }}</ref> and is shown to promote the development of many cancers.<ref>{{cite journal | title = The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers | journal = The New England Journal of Medicine | volume = 330 | issue = 15 | pages = 1029–1035 | date = April 1994 | pmid = 8127329 | doi = 10.1056/NEJM199404143301501 | vauthors = Alpha-Tocopherol BC }}</ref><ref>{{cite journal | vauthors = Goodman GE, Thornquist MD, Balmes J, Cullen MR, Meyskens FL, Omenn GS, Valanis B, Williams JH | title = The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements | journal = Journal of the National Cancer Institute | volume = 96 | issue = 23 | pages = 1743–1750 | date = December 2004 | pmid = 15572756 | doi = 10.1093/jnci/djh320 }}</ref>

There are two sources of dietary vitamin A. Retinyl ester or retinol forms, which are immediately available to the body or [[carotene]] precursors, also known as provitamins, which must be converted to active forms by the body. These are obtained from fruits and vegetables containing yellow, orange and dark green pigments, known as [[carotenoid]]s, the most well-known being β-carotene.<ref>{{cite journal | vauthors = Burri BJ, Clifford AJ | title = Carotenoid and retinoid metabolism: insights from isotope studies | journal = Archives of Biochemistry and Biophysics | volume = 430 | issue = 1 | pages = 110–119 | date = October 2004 | pmid = 15325918 | doi = 10.1016/j.abb.2004.04.028 | series = Highlight issue on Carotenoids }}</ref> For this reason, amounts of vitamin A are measured in Retinol Equivalents (RE). One RE is equivalent to 0.001&nbsp;mg of retinol, or 0.006&nbsp;mg of β-carotene, or 3.3 International Units of vitamin A.

Vitamin A is fat-soluble and is stored in the liver and fat tissue.<ref>{{cite journal | vauthors = Steinhoff JS, Wagner C, Dähnhardt HE, Košić K, Meng Y, Taschler U, Pajed L, Yang N, Wulff S, Kiefer MF, Petricek KM, Flores RE, Li C, Dittrich S, Sommerfeld M, Guillou H, Henze A, Raila J, Wowro SJ, Schoiswohl G, Lass A, Schupp M | title = Adipocyte HSL is required for maintaining circulating vitamin A and RBP4 levels during fasting | journal = EMBO Reports | volume = 25 | issue = 7 | pages = 2878–2895 | date = July 2024 | pmid = 38769419 | pmc = 11239848 | doi = 10.1038/s44319-024-00158-x }}</ref> When required by a particular part of the body, the liver releases some vitamin A, which is carried by the blood and delivered to the target cells and tissues.<ref>{{cite journal | vauthors = Amengual J, Zhang N, Kemerer M, Maeda T, Palczewski K, Von Lintig J | title = STRA6 is critical for cellular vitamin A uptake and homeostasis | journal = Human Molecular Genetics | volume = 23 | issue = 20 | pages = 5402–5417 | date = October 2014 | pmid = 24852372 | pmc = 4168826 | doi = 10.1093/hmg/ddu258 }}</ref>

===Dietary intake===
The [[Dietary Reference Intake]] (DRI) Recommended Daily Amount (RDA) for vitamin A for a 25-year-old male is 900 micrograms/day, or 3000 IU. [[National Health Service]] daily recommended values are slightly lower at 700 micrograms for men and 600 micrograms for women.<ref>{{cite web|date=23 October 2017|title=Vitamins and minerals - Vitamin A|url=https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-a/|access-date=18 February 2023|website=nhs.uk|language=en}}</ref>

During the absorption process in the [[intestine]]s, retinol is incorporated into [[chylomicron]]s as the ester form, and it is these particles that mediate transport to the [[liver]]. Liver cells store vitamin A as the ester, and when retinol is needed in other tissues, it is de-esterifed and released into the blood as the alcohol. Retinol then attaches to a serum carrier, [[retinol binding protein]], for transport to target tissues.<ref>{{cite journal | vauthors = Amengual J, Zhang N, Kemerer M, Maeda T, Palczewski K, Von Lintig J | title = STRA6 is critical for cellular vitamin A uptake and homeostasis | journal = Human Molecular Genetics | volume = 23 | issue = 20 | pages = 5402–5417 | date = October 2014 | pmid = 24852372 | pmc = 4168826 | doi = 10.1093/hmg/ddu258 }}</ref> A binding protein inside cells, cellular retinoic acid binding protein, serves to store and move retinoic acid [[intracellular]]ly.

===Deficiency===
{{main|Vitamin A deficiency}}
[[Image:Vitamin A deficiency.PNG|right|thumb|360px|Prevalence of vitamin A deficiency in 1995]]
Vitamin A deficiency is common in developing countries but rarely seen in developed countries. Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A.<ref>{{cite web |url=https://www.who.int/nutrition/topics/vad/en/ |title=Micronutrient deficiencies - Vitamin A deficiency |author=<!--Not stated--> |date=18 April 2018 |website=World Health Organization |access-date=18 April 2018 }}</ref> Vitamin A deficiency in expecting mothers increases the mortality rate of children shortly after childbirth.<ref>{{cite journal | vauthors = Akhtar S, Ahmed A, Randhawa MA, Atukorala S, Arlappa N, Ismail T, Ali Z | title = Prevalence of vitamin A deficiency in South Asia: causes, outcomes, and possible remedies | journal = Journal of Health, Population, and Nutrition | volume = 31 | issue = 4 | pages = 413–423 | date = December 2013 | pmid = 24592582 | pmc = 3905635 | doi = 10.3329/jhpn.v31i4.19975 }}</ref> [[Night blindness]] is one of the first signs of vitamin A deficiency. Vitamin A deficiency contributes to blindness by depleting the necessary form needed for rhodopsin.<ref name=bs/>

===Sources===
{{See also|Vitamin_A#Sources}}

Retinoids are found naturally only in foods of animal origin. Each of the following contains at least 0.15&nbsp;mg of retinoids per {{convert|1.75|-|7|oz|g|abbr=on}}:
* [[Cod liver oil]]
* [[Butter]]
* [[Liver (food)|Liver]] (beef, pork, chicken, turkey, fish)
* [[Egg (food)|Eggs]]
* [[Cheese]], [[milk]]<ref>{{cite book | vauthors = Brown JE | date = 2002 | title = Vitamins and Your Health. Nutrition Now | edition = 3rd | pages = 1–20 }}</ref>