Vitamin A is a fat-soluble vitamin needed for vision, immune function, growth and reproduction. It comes as preformed vitamin A (retinol and retinyl esters) from animal foods and supplements, and as provitamin A carotenoids such as beta-carotene, which the body converts. Supplements are used to cover low intake.
Also known as: retinol, retinyl palmitate, beta-carotene.
ODS lists a Recommended Dietary Allowance of 900 mcg RAE (retinol activity equivalents) a day for men and 700 mcg RAE for women, 770 mcg RAE in pregnancy and 1,300 mcg RAE while breastfeeding. The Tolerable Upper Intake Level for adults is 3,000 mcg a day of preformed vitamin A (retinol and its esters); it does not apply to beta-carotene. Stand-alone supplements commonly contain 3,000 mcg RAE; multivitamins often 750 to 1,050 mcg RAE.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. Prescription retinoids (such as isotretinoin and acitretin) are drugs made from vitamin A.
ODS says the body stores extra vitamin A in the liver, so it can build up. Very high single doses cause severe headache, blurred vision, nausea and dizziness; regular high intake can cause dry skin, joint pain, fatigue and abnormal liver tests. Preformed vitamin A above the upper limit can cause birth defects, and experts advise anyone who is or might be pregnant, or breastfeeding, not to take more than 3,000 mcg RAE (10,000 IU) a day. Beta-carotene does not cause birth defects, but in two large trials high-dose beta-carotene raised lung cancer risk in smokers (and in some asbestos-exposed workers).
Interactions, per ODS: the weight-loss drug orlistat (Alli, Xenical) reduces absorption of vitamin A and other fat-soluble vitamins, and its makers recommend a multivitamin; oral retinoids such as acitretin and bexarotene taken with vitamin A supplements raise the risk of vitamin A toxicity.
We could not find a single published half-life or time to peak for vitamin A that applies to a supplement dose, so we do not list one. It is stored mainly in the liver. ODS gives absorption of 70% to 90% for preformed vitamin A from supplements and 8.7% to 65% for beta-carotene.
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