Ask the Experts
For: New Advice About Vitamin A, July 2002
Q: How
much vitamin A is dangerous? I take 20,000 units a day.
V.B., VIA THE INTERNET
A: That is too much, especially
if you're a woman who may become pregnant. It's also too much
for children. There is no reason to take a separate vitamin A supplement.
The government's Daily Value—the number used on food labels
and vitamin bottles—is 5,000 IU (international units); the RDA is
about half that much. Many multivitamins contain 5,000 IU, which is okay.
Vitamin A is a fat-soluble vitamin; the body stores such vitamins. Thus, dangerous levels can build up if you take large doses over time. Side effects, including headaches, itchy skin, and hair loss, may occur starting at about 30,000 IU a day taken long-term.
The biggest risk is for women of childbearing age who take
vitamin A pills. It used to be thought that only very high doses—over
50,000 IU a day—were dangerous. But a few years ago a study found
that women taking more than 10,000 IU a day from supplements had nearly
five times the risk of birth defects. Recently,
the government set 10,000 IU as the upper limit for A.
Only a few foods are rich in vitamin A: fortified milk, egg yolks, and particularly liver and fish oil. The body converts beta carotene and some other carotenoids into vitamin A, but there is no risk of overdose with carotenoids, since the body carefully controls their conversion to vitamin A. Check the label of your vitamin supplement: often it will state that the vitamin A comes, at least in part, in the form of beta carotene.
If you eat a variety of fruits and vegetables, which are
rich in carotenoids, you don't need to worry about getting enough
vitamin A.
UC Berkeley Wellness Letter, June 2001
