Pregnant women should avoid vitamin and mineral supplements, except iron, and get the extra nutrients they need from a balanced diet, a National Academy of Sciences committee recommended today in a report that is sure to surprise obstetricians.
Multiple-vitamin supplements and iron tablets are commonly prescribed to women throughout pregnancy to ensure the proper development of the fetus. In addition, recent research has indicated that folic acid supplements might help prevent birth defects involving the spinal cord, such as spina bifida.
But the 11-member committee of medical and nutritional experts from the Institute of Medicine suggested that the fetus may suffer if vitamin supplementation replaces a well-balanced diet. Moreover, the committee concluded that more research is needed before widespread supplementation of folic acid can be advised to prevent spinal-cord defects, called neural tube defects.
The report encouraged health-care practitioners to identify special problems that might affect a pregnant woman's nutritional needs and to counsel women on how to improve their diets. It is believed that this practice can eliminate the need for widely distributed prenatal multivitamin supplements. Supplementation, the committee said, should be a final intervention.
"There is considerable variation in nutrient requirements among individuals," the report added. Food, the committee said, is the "normal vehicle for delivering nutrients and nutrient supplementation (is) an intervention (that should be) based on evidence of benefit as well as lack of harmful effects."
The committee expressed concern that vitamin supplements might inhibit absorption of various minerals because the nutrients can interact in adverse ways. With normal food intake, nutrients are generally not consumed in such large concentrations at any one time as to interact or overwhelm each other.
But taken as a supplement, iron, for example, can inhibit the absorption of zinc, and zinc can affect the way the body handles copper, the committee said. And Vitamin A, or retinol, supplements can cause abnormal fetal development when prescribed during the first three months of pregnancy.
American College of Obstetricians and Gynecologists' guidelines also discourage routine vitamin supplementation during pregnancy with the exception of iron and folic acid supplements, said Kate Ruddon, spokeswoman for the Washington-based group.
