Q: Many multivitamin pills contain 3,500 IU of vitamin A, in some mix of a vitamin A compound and beta carotene. I'm wondering if all that vitamin A is safe. If a person drinks milk and has a couple of vegetables each day, is the vitamin A in the pill doing any harm?
--L.F.
A: Vitamin A is a family of compounds that play a role in vision, bone health, cell division and the regulation of the immune system. Retinol is one of the most usable forms of vitamin A. Several carotenoids, the darkly colored pigments found in many plant foods, can be converted to vitamin A, but beta carotene is the carotenoid that is most efficiently converted to vitamin A. Retinol is found in foods that come from animals, such as whole eggs, milk and liver. Most fat-free milk sold in the U.S. is fortified with vitamin A to replace the amount lost when the fat is removed. Most people get their retinol from milk, margarine, eggs, beef liver and fortified breakfast cereals, whereas major contributors of vitamin A from carotenoids are carrots, cantaloupes, sweet potatoes and spinach.
Although diets rich in vegetables are linked with improved health, it's also true that too much vitamin A is not a good thing. A 2002 Harvard study of more than 72,000 nurses showed that those who consumed high levels of vitamin A from foods, multivitamins and supplements had a 48% higher risk for hip fracture than nurses who had the lowest intake of vitamin A. Notably, nurses who got high levels of vitamin A just from foods rather than supplements also had higher risk, possibly indicating that too many foods are now fortified with the vitamin. Milk, margarine and breakfast cereals are fortified with vitamin A. High intake of vitamin A has also been associated with a higher risk of birth defects.
Most multivitamins do contain some level of vitamin A, but whether it's going to result in too much vitamin A for you depends on your diet. The daily value for vitamin A is 5,000 international units, so a typical multivitamin containing 3,500 IUs represents about 70% of your daily needs. However, the tolerable upper intake for vitamin A, which indicates how much it's safe to consume without worrying about toxicity, is 10,000 IUs. A cup of fortified skim milk has about 500 IUs of vitamin A, a cup of cantaloupe has 5,400 IUs and a half cup of boiled carrots has more than 13,000 IUs.
The Office of Dietary Supplements offers a useful fact sheet on vitamin A that includes listings for the vitamin A content of several foods. If you think you typically are taking in high levels of vitamin A you might reconsider your multivitamin and look for a product that contains lower levels of vitamin A. The fact sheet can be found at: dietary-supplements.info.nih.gov |
