Vitamin A does much more than help you see in the dark. It stimulates the production and activity of white blood cells, takes part in remodeling bone, helps maintain the health of endothelial cells (those lining the body’s interior surfaces), and regulates cell growth and division. This latter role had researchers exploring for years whether insufficient vitamin A caused cancer. Several studies have dashed this hypothesis, as have randomized trials of supplements containing beta carotene, a precursor of vitamin A.
Although it’s relatively easy to get too little vitamin A, it’s also easy to get too much. Intake of up to 10,000 IU, twice the current recommended daily level, is thought to be safe. However, there is some evidence that this much preformed vitamin A might increase the risk of hip fracture or some birth defects.
Optimal Intake: The current recommended intake of vitamin A is 5,000 IU for men and 4,000 IU for women. Many breakfast cereals, juices, dairy products, and other foods are fortified with vitamin A. Many fruits and vegetables, and some supplements, also contain beta-carotene and other vitamin A precursors, which the body can turn into vitamin A. In contrast to preformed vitamin A, beta-carotene is not toxic even at high levels of intake. The body can form vitamin A from beta-carotene as needed, and there is no need to monitor intake levels, as there is with preformed vitamin A. Therefore, it is preferable to choose a vitamin supplement that has all or the vast majority of its vitamin A in the form of beta-carotene. Another reason to avoid too much preformed vitamin A is that it may interfere with the beneficial actions of vitamin D.
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