Uses and misuses of vitamin A.

Vitamin A, which is available from dietary sources, vitamin supplements, and fortified products, affects numerous bodily processes through its impact on cellular differentiation. More than 300 genes are regulated by the rapid action of the vitamin. It has recently been recognized that mild vitamin A deficiency is widespread among children and pregnant women in developing countries. This deficiency increases severity of infectious diseases, iron-related anemia, and growth disturbances. Improving the vitamin A status of all deficient children could avert a million or more deaths annually, and administration of high-dose vitamin A has been advised for treatment of measles. There is also an apparent association between high beta carotene status (which may represent vitamin A status) and lower rates of some forms of cancer, but this has yet to be confirmed. Supplementation programs in developing countries rely on periodic administration of high-dose vitamin A in doses of 100,000 IU orally for those under 1 year old and 200,000 IU for those older once every 3-6 months. The optimal dosing schedule is unknown, but no cases of death have been linked to isolated vitamin A toxicity. Experts also disagree about the window of safety during which a high-dose of vitamin A can be given to pregnant and postpartum women without causing teratogenicity. It is unwise to administer high-dose vitamin A to women of reproductive age after the first 6 weeks postpartum. All women at risk should receive small daily doses or 20,000 IU weekly doses. In the US, where general dietary status is good, women should not use more than 8000 IU supplements except when indicated for a specific reason.