Women who take multivitamins around the time of conception are less likely than others to give birth to children with certain birth defects, according to a new study that raises the possibility of reducing the incidence of spina bifida and anencephaly.
The federal researchers found that women who took multivitamins regularly in the three months before and after becoming pregnant were 50% less likely to produce children with brain and spinal cord malformations known as neural-tube defects.
Their study, published today in the Journal of the American Medical Assn., is "the best evidence to date in the United States" that vitamin supplementation might cut the occurrence of conditions now affecting one in every 1,000 babies, one expert said in an editorial accompanying the study.
However, Dr. Joseph Mulinare, who headed the study of 3,176 babies born in Atlanta between 1968 and 1980, said further studies would have to confirm the findings before his team would advise women to take multivitamins to cut their birth-defect risk.
It is not yet clear that the reduced risk resulted directly from vitamins or from some other characteristic common to women who take vitamins, he said. For example, some research has suggested that vitamin users also have more nutritious diets.
"It could be the multivitamins are having an effect on the fetus," said Mulinare, a medical epidemiologist with the U.S. Centers for Disease Control. "Or it could be something special about women who are multivitamin users versus women who are not."
Dr. Lewis B. Holmes of Massachusetts General Hospital in Boston said in the editorial that the research raises an "exciting possibility," but that efforts to educate women about other preventable defects have encountered only limited success.
Holmes predicted that "the biggest challenge" posed by the study would be getting women of childbearing age "to hear and follow this simple advice."
Neural-tube defects are malformations of the brain and spinal cord that begin during gestation. The most common are spina bifida, in which a malformed spinal column leaves some of the nervous system exposed, and anencephaly, in which much of the brain is missing.
The causes of neural-tube defects are unclear. Both hereditary and environmental factors have been considered. But because of the increased incidence of such defects among poorer people, many researchers have suspected that nutrition plays a role.
Mulinare's study found that women who took either prenatal vitamins prescribed by a physician or over-the-counter multivitamins incorporating some six to eight vitamins were half as likely as the others to have had a child with a neural-tube defect.
The reduction in risk was even greater--closer to 60%--for spina bifida.
Those women reported having taken vitamins at least three times a week during the six-month period studied. Women who began taking vitamins later--for example, during the first or second month of pregnancy--also had reduced risk but not to the same degree.
Mulinare said the multivitamins in question would have consisted of Vitamins A, B, B12 and D. Some would have also included B1, B2, folic acid and iron.
The study did not explain how vitamins might prevent birth defects. But Holmes speculated that vitamins might somehow protect the embryo from the influence of mutant genes that he believes may some day be shown to have a role in the development of defects.
While Mulinare said he knew of no problems that can be caused by moderate use of appropriate vitamins by pregnant women under medical supervision, the researchers warned that some vitamins can be harmful to a fetus, especially in large amounts.
"Because vitamins may . . . have adverse effects on the fetus, prudence and counsel in considering the use of multivitamins is required," they wrote.