Vitamin A

Last Updated: January 8, 2024

Vitamin A describes a group of metabolites involved in cell and tissue growth, and several bodily functions, including vision, bone metabolism, and immune function. Vitamin A metabolites include preformed vitamin A — retinols, retinals, retinyl esters, and retinoic acids — and precursors (i.e., provitamin A molecules) like beta-carotene, which can be converted by the body into the other forms of vitamin A.

Vitamin A is most often used for

What is vitamin A?

Vitamin A describes a group of fat-soluble metabolites that include preformed vitamin A molecules — retinols, retinals, retinyl esters, retinoic acids — and provitamin A molecules — carotenoids like beta-carotene — which are precursors that the body can convert into the other forms of vitamin A.[3][4][5] Vitamin A metabolites are involved in cell and tissue growth and in several bodily functions, including vision, bone metabolism, and immune function.[3][4]

Because they are fat soluble, vitamin A metabolites can be stored in the body (mainly in the liver) as a retinyl ester.[6][7][5][3] However, dietary intake is necessary because humans cannot synthesize vitamin A from scratch.[6][7][3][4] Humans obtain preformed vitamin A — retinols, retinals, retinyl esters, and retinoic acids — from animal products (e.g., fish, eggs, dairy, liver), and obtain provitamin A carotenoids (like beta-carotene) from plants (e.g., sweet potatoes, carrots, leafy greens); the latter can be converted to preformed vitamin A by the body.[1][5] In some countries, some foods — milk, margarine, cereals, etc. — are also fortified with vitamin A.[8][9][10][11]

Vitamin A is also taken as a dietary supplement. Such supplements typically contain preformed vitamin A (retinyl acetate or retinyl palmitate), provitamin A (beta-carotene), or a combination of both.[12] Vitamin A is also found in high levels in some fish oil supplements, such as cod liver oil, and in many multivitamins.[12]

What are vitamin A’s main benefits?

Sufficient amounts of vitamin A can be obtained through a balanced diet, but vitamin A deficiency can occur due to insufficient intake.[1][3][4] Supplementation with vitamin A is used to treat vitamin A deficiency, which is most common in malnourished infants/children living in developing countries.[1][3][4] The evidence shows that supplementation with vitamin A can improve growth, vision, and survival in malnourished infants/children[13][14][15][16][17][18] and in premature babies.[19][20] However, the precise recommendations for treating vitamin A deficiency are unclear because results are inconsistent among studies.[14][15][16][17][18][19][20]

Observational studies show that higher dietary intake of vitamin A, which includes total vitamin A intake from all sources (foods, drinks, and supplements), is associated with a reduced risk of depression.[21] However, this association is derived from cross-sectional and cohort study designs in which vitamin A intake was estimated from historical diet recall using food frequency questionnaires. This makes it difficult to prove a causal link between vitamin A intake and depression.

Besides dietary vitamin A, all-trans retinoic acid (Tretinoin) and 13-cis-retinoic acid (Isotretinoin) are types of vitamin A used in prescription drugs that are effective in treating acne.[22][23][24]

What are vitamin A’s main drawbacks?

High intakes of preformed vitamin A can cause serious side effects — symptoms include severe headache, blurred vision, nausea, dizziness, muscle aches, and problems with coordination.[1][25][26][12][27]

Excessive intakes of preformed vitamin A have been associated with an increased risk of bone problems — e.g., osteoporosis and hip fracture[28][29] — and some types of cancer, including ovarian cancer,[30] pancreatic cancer,[31] lung cancer,[32] and gastric cancer.[33] However, this evidence is derived from observational studies using cross-sectional and cohort study designs in which vitamin A intake data was estimated from historical diet recall using food frequency questionnaires. This makes it difficult to prove the causality between vitamin A intake and disease risk.

Excessive intake of preformed vitamin A during pregnancy can also cause birth defects, and excessive intake when breastfeeding can impair a child’s growth.[1][25][26][12] Therefore, high-dose supplementation with preformed vitamin A is not recommended when pregnant or lactating — consult your doctor if you are unsure.

In severe cases, excessive intake of preformed vitamin A can cause coma and death,[1][25][26][12][27] and supplementation with high doses of vitamin A has also been associated with increased mortality in well-nourished populations.[25]

There are also several drug interactions with Vitamin A, including, but not limited to, several antibiotics, some weight loss drugs (e.g., orlistat), and vitamin-A-containing drugs (e.g., isotretinoin). Always consult your doctor if you are taking over-the-counter or prescription medicines and planning to use a vitamin A supplement.

Because of the side effects and potential toxicity, there is an upper limit for total daily intake of preformed vitamin A (from food, beverages, and supplements combined):[1][2]

AgesUpper limit of daily intake
Birth to 12 months600 micrograms (mcg or µg)
Children 1–3 years600 mcg
Children 4–8 years900 mcg
Children 9–13 years1,700 mcg
Teens 14–18 years2,800 mcg
Adults 19 years and older3,000 mcg

Unlike preformed vitamin A, high intake of beta-carotene (a provitamin A carotenoid) is not associated with serious side effects or health problems, and beta-carotene does not have an upper limit of intake. However, this does not mean that taking a higher-than-recommended dose of beta-carotene induces a greater effect.

How does vitamin A work?

When ingested, beta-carotene, a provitamin A carotenoid, is converted in the gastrointestinal system into a retinal form of vitamin A, which can be subsequently converted into retinol, retinoic acid, or retinyl ester forms of vitamin A.[5][3][6][7] Retinyl esters are the storage form of vitamin A, and are primarily stored in the liver.[5][3][6]

The metabolism of vitamin A is complex: there are many interconvertible forms, and each has a different role.[6][3][12][7] For example, different types of retinols, retinals, and retinyl esters are precursor molecules to the synthesis of rhodopsin, a pigment involved in vision;[3] retinols can act as cofactors in several enzymatic processes;[12] and retinoic acids directly regulate gene expression while also regulating vitamin A metabolism by, for example, modifying the intestinal absorption of beta-carotene.[3]

What else is Vitamin A known as?
Note that Vitamin A is also known as:
  • retinol
  • retinal
  • retinoic acid
  • tretinoin
  • beta-carotene
  • Retinyl ester
  • all-trans retinoic acid
  • 13-cis-retinoic acid
Dosage information

Recommended intake is similar between males and females, except during pregnancy and lactation when vitamin A requirements are elevated. The recommended dietary allowances (RDA) are:[1][2]

AgesRecommended daily intake
Birth to 6 months400 micrograms (mcg, or µg)
Infants 7–12 months500 mcg
Children 1–3 years300 mcg
Children 4–8 years400 mcg
Children 9–13 years600 mcg
Teen males 14–18 years900 mcg
Teen females 14–18 years700 mcg
Teen females, pregnant750 mcg
Teen females, breastfeeding1,200 mcg
Adult males900 mcg
Adult females700 mcg
Adult females, pregnant770 mcg
Adult females, breastfeeding1,300 mcg

Due to potential toxicity, the upper limit of total daily intake of preformed vitamin A (from food, beverages, and supplements combined) is as follows:[1][2]

AgesUpper limit of daily intake
Birth to 12 months600 mcg
Children 1–3 years600 mcg
Children 4–8 years900 mcg
Children 9–13 years1,700 mcg
Teens 14–18 years2,800 mcg
Adults 19 years and older3,000 mcg
Examine Database: Vitamin A
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References
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Examine Database References
  1. Hyperpigmentation - Weinstein GD, Nigra TP, Pochi PE, Savin RC, Allan A, Benik K, Jeffes E, Lufrano L, Thorne EGTopical tretinoin for treatment of photodamaged skin. A multicenter studyArch Dermatol.(1991 May)
  2. Hyperpigmentation - Griffiths CE, Goldfarb MT, Finkel LJ, Roulia V, Bonawitz M, Hamilton TA, Ellis CN, Voorhees JJTopical tretinoin (retinoic acid) treatment of hyperpigmented lesions associated with photoaging in Chinese and Japanese patients: a vehicle-controlled trialJ Am Acad Dermatol.(1994 Jan)
  3. Hyperpigmentation - Griffiths CE, Kang S, Ellis CN, Kim KJ, Finkel LJ, Ortiz-Ferrer LC, White GM, Hamilton TA, Voorhees JJTwo concentrations of topical tretinoin (retinoic acid) cause similar improvement of photoaging but different degrees of irritation. A double-blind, vehicle-controlled comparison of 0.1% and 0.025% tretinoin creamsArch Dermatol.(1995 Sep)
  4. Skin Thickness - Weiss JS, Ellis CN, Headington JT, Tincoff T, Hamilton TA, Voorhees JJTopical tretinoin improves photoaged skin. A double-blind vehicle-controlled studyJAMA.(1988 Jan 22-29)
  5. Skin Quality - Kafi R, Kwak HS, Schumacher WE, Cho S, Hanft VN, Hamilton TA, King AL, Neal JD, Varani J, Fisher GJ, Voorhees JJ, Kang SImprovement of naturally aged skin with vitamin A (retinol)Arch Dermatol.(2007 May)
  6. Multiple Sclerosis Symptoms - Sama Bitarafan, Aliakbar Saboor-Yaraghi, Mohammad-Ali Sahraian, Danesh Soltani, Shahriar Nafissi, Mansoureh Togha, Nahid Beladi Moghadam, Tina Roostaei, Niyaz Mohammadzadeh Honarvar, Mohammad-Hossein HarirchianEffect of Vitamin A Supplementation on fatigue and depression in Multiple Sclerosis patients: A Double-Blind Placebo-Controlled Clinical TrialIran J Allergy Asthma Immunol.(2016 Feb)
  7. Infant Death Risk - Mayo-Wilson E, Imdad A, Herzer K, Yakoob MY, Bhutta ZAVitamin A supplements for preventing mortality, illness, and blindness in children aged under 5: systematic review and meta-analysis.BMJ.(2011-Aug-25)
  8. Infant Death Risk - Aamer Imdad, Zunirah Ahmed, Zulfiqar A BhuttaVitamin A supplementation for the prevention of morbidity and mortality in infants one to six months of ageCochrane Database Syst Rev.(2016 Sep 28)
  9. Infant Death Risk - Imdad A, Mayo-Wilson E, Haykal MR, Regan A, Sidhu J, Smith A, Bhutta ZAVitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age.Cochrane Database Syst Rev.(2022-Mar-16)
  10. Infant Death Risk - Haider BA, Sharma R, Bhutta ZANeonatal vitamin A supplementation for the prevention of mortality and morbidity in term neonates in low and middle income countries.Cochrane Database Syst Rev.(2017-Feb-24)
  11. Infant Death Risk - Darlow BA, Graham PJ, Rojas-Reyes MXVitamin A supplementation to prevent mortality and short- and long-term morbidity in very low birth weight infants.Cochrane Database Syst Rev.(2016-Aug-22)
  12. Infant Death Risk - Rakshasbhuvankar AA, Pillow JJ, Simmer KN, Patole SKVitamin A supplementation in very-preterm or very-low-birth-weight infants to prevent morbidity and mortality: a systematic review and meta-analysis of randomized trials.Am J Clin Nutr.(2021-Dec-01)
  13. Lung Function - Phattraprayoon N, Ungtrakul T, Soonklang K, Susantitaphong POral vitamin A supplementation in preterm infants to improve health outcomes: A systematic review and meta-analysis.PLoS One.(2022)
  14. Acne Symptoms - Costa CS, Bagatin E, Martimbianco ALC, da Silva EM, Lúcio MM, Magin P, Riera ROral isotretinoin for acne.Cochrane Database Syst Rev.(2018-Nov-24)