Public health policy should be reconsidered concerning the use of vitamin and mineral supplements by all women -- from their teen years to menopause -- who may eventually bear children, recommends a nutritionist at the University of California, Davis, in a special February issue of the American Journal of Clinical Nutrition. "Research findings indicate that the risk of certain birth defects can be dramatically lowered by enhancing the nutritional status of the mother prior to and after conception," said Carl Keen, chair of the UC Davis nutrition department and an authority on nutrition and human development. In collaboration with Sheri Zidenberg-Cherr, a UC Davis Cooperative Extension nutritionist, Keen recently surveyed previous studies related to the impact of nutrition on the outcome of pregnancies. The journal article summarizes their review. "Since laboratory studies on animal models indicate that nutritional deficiencies have profound effects on the health of the fetus very early in conception, it is advisable that a woman already be regularly taking supplements at the time of conception, rather than waiting until she realizes that she is pregnant," he said. Birth defects occur in approximately 3 percent of all infants and are the leading cause of death among children in the United States, according to Keen, co-editor of the 1993 book "Maternal Nutrition and Pregnancy Outcome." He notes that there is substantial evidence that maternal diet and nutritional status can significantly affect the outcome of a pregnancy. For example, several studies have found that mothers whose diets were considered to be good or excellent had pregnancies with remarkably fewer complications than did those whose diets were poor. "Previous studies indicate that large segments of the U.S. female population of childbearing age consume woefully inadequate amounts of major nutrients," said Keen. "Unfortunately, teens and women of lower socioeconomic status -- both groups which are already at higher risk -- tend to consume lower quality diets and to be less likely to take supplements." Perhaps one of the most compelling cases for the use of supplements concerns the relationship of maternal diet to devastating neural tube defects like spina bifida, which results in a gap in the bone surrounding the spinal cord, and anencephaly, in which the brain or the spinal cord does not form. A 1991 British study showed that women who received a folate supplement had a 72 percent reduction in the risk of another neural tube defect during pregnancy. The U.S. Centers for Disease Control and Prevention now recommends that all women who have had a previous pregnancy with a neural tube defect consume 4 mg of folate per day for at least one month before conception and through the first three months of pregnancy. As further support, Keen cites the virtual eradication of iodine deficiency-induced cretinism in many countries by supplementing certain foods with iodine. Marked by a severe lack of thyroid function during infancy, cretinism results in dwarfism, mental deficiency, puffy facial features and lack of muscle coordination. It now occurs only in parts of the world where supplemental iodine is not available. Research suggests that vitamin supplementation may also protect against cleft palate and cleft lip. These conditions occur in about one in every 700 infants. One study found that among women who had already had one child with a cleft lip or cleft palate, those who received no vitamin supplements had a recurrence rate of 6.4 percent, while those who received supplements had no recurrence. Keen also cites studies that indicate that calcium and trace nutrients such as zinc and magnesium are important to the outcome of pregnancies. "While the evidence definitely suggests that vitamin-mineral supplement use can be associated with a reduced risk for pregnancy complications, including birth defects, any public policy changes based on that evidence should be pursued with due caution," Keen said. He noted that there is the danger that some individuals might neglect a proper diet, assuming that the supplement provides for all of their nutritional needs, and also that supplementation might inadvertently lead to the consumption of excessive levels of some nutrients. Funding for this overview study was provided by the National Institutes of Health.