Vitamin A
Vitamin A is the name of a group of fat-soluble retinoids, primarily retinol and retinyl esters. Most of the body’s vitamin A is stored in the liver in the form of retinyl esters. The units of measurement for vitamin A are now mcg RAE, but International Units (IUs) were previously used. Pregnant women need extra vitamin A for fetal growth and tissue maintenance and to support their own metabolism. Preterm infants with vitamin A deficiency have a higher risk of eye and chronic lung diseases. The most common clinical sign of vitamin A deficiency is xerophthalmia, and the first sign is night blindness, or the inability to see in low light or darkness.
Where to get it
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Active compounds & mechanisms
Key compounds: Retinoids, Retinol, Retinyl esters
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
NIH ODS says some clinical trial evidence suggests that supplemental vitamin A might reduce the risk of certain cancers. Among nonsmokers, beta-carotene and vitamin A supplements do not appear to affect the risk of cancer.
Mixed evidenceSome support. Results are mixed
Study details
NIH ODS: “Some clinical trial evidence suggests that supplemental vitamin A might reduce the risk of certain cancers” NIH ODS: “Among nonsmokers, beta-carotene and vitamin A supplements do not appear to affect the risk of cancer.”
Source: NIH ODS, Vitamin A — Health Professional Fact Sheet (Updated March 10, 2025), Vitamin A and Health (cancer) View source
For age-related macular degeneration, NIH ODS says supplements containing carotenoids with antioxidant functions, such as beta-carotene, lutein, and zeaxanthin, might be useful.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
NIH ODS: “supplements containing carotenoids with antioxidant functions, such as beta-carotene, lutein, and zeaxanthin, might be useful”
Source: NIH ODS, Vitamin A — Health Professional Fact Sheet (Updated March 10, 2025), Vitamin A and Health (age-related macular degeneration) View source
Research suggests that vitamin A supplementation reduces the risk of measles in children. However, vitamin A supplementation does not appear to reduce the risk of death from measles.
Mixed evidenceSome support. Results are mixed
Study details
NIH ODS: “Research suggests that vitamin A supplementation reduces the risk of measles in children” NIH ODS: “However, vitamin A supplementation does not appear to reduce the risk of death from measles.”
Source: NIH ODS, Vitamin A — Health Professional Fact Sheet (Updated March 10, 2025), Vitamin A and Health (measles) View source
Dosage
| Form | Amount |
|---|---|
| Any form | No standard dose is listed by our sources. |
Side effects
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Liver abnormalities (increased risk with high intakes of preformed vitamin A)Well documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Congenital birth defects, which can include malformations of the eye, skull, lungs, and heart (total intakes of preformed vitamin A above the UL)Well documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Increased risk of lung cancer and mortality with a large amount of beta-carotene (20 mg/day) in male smokers (ATBC trial)ReportedCase reports only | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
Safety & interactions
Safety
Because vitamin A is fat soluble, the body stores excess amounts, primarily in the liver, and these levels can accumulate. The FNB has established ULs for preformed vitamin A that apply to both food and supplement intakes, and based these ULs on the amounts associated with an increased risk of liver abnormalities in men and women. Total intakes of preformed vitamin A that exceed the UL, as well as some retinoid medications, can cause congenital birth defects. Unlike preformed vitamin A, beta-carotene is not known to be teratogenic or lead to reproductive toxicity, and the FNB has not established ULs for beta-carotene and other provitamin A carotenoids. However, the CARET and ATBC study results suggest that large supplemental doses of beta-carotene, with or without retinyl palmitate, have detrimental effects in current or former smokers and workers exposed to asbestos. The ATBC trial found that supplementation with a large amount of beta-carotene (20 mg/day) increased the risk of lung cancer and mortality in male smokers. The FNB advises against the use of beta-carotene supplements for the general population.
Contraindications
Experts advise women who are or might be pregnant and those who are lactating not to take high doses (more than 3,000 mcg RAE [10,000 IU] daily) of vitamin A supplements. Total intakes of preformed vitamin A that exceed the UL can cause congenital birth defects, and these birth defects can include malformations of the eye, skull, lungs, and heart. The CARET and ATBC study results suggest that large supplemental doses of beta-carotene have detrimental effects in current or former smokers and workers exposed to asbestos. If you take a retinoid medication or orlistat, see Drug interactions.
Drug interactions
NIH ODS says orlistat (Alli, Xenical), a weight-loss treatment, can decrease the absorption of vitamin A. The manufacturers of Alli and Xenical recommend that patients on orlistat take a multivitamin supplement.
NIH ODS says retinoids can increase the risk of hypervitaminosis A (an excess of vitamin A) when taken in combination with vitamin A supplements. Examples include the psoriasis treatment acitretin (Soriatane) and bexarotene (Targretin). Some retinoid medications can also cause congenital birth defects.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
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