The U.S. Government’s plan to fortify grains with the vitamin folic acid to help prevent a devastating class of birth defects is likely to reduce the risk of these defects substantially, according to an early study by researchers in Ireland and at the National Institute of Child Health and Human Development (NICHD). Some researchers had feared that the amount of folate that will be added to grains-kept low so as not to jeopardize the health of those who may not need extra folate-is not enough to prevent the birth defects.

The study, which appeared in the December 6 issue of The Lancet, was led by Sean Daly, of Coombe Women’s Hospital in Dublin (now at Thomas Jefferson Hospital in Philadelphia, PA). The research team also included members from the NICHD, from Trinity College in Dublin and from the Health Research Board of Ireland.

Briefly, the study treated a group of women of childbearing age with different doses of folic acid (0, 100, 200, or 400 micrograms) for 6 months to determine how much was needed to raise their blood folate to a level known to protect against most neural tube defects. The researchers found women receiving 100 micrograms reached a level that would prevent 22 percent of NTDs. The women receiving 200 micrograms did even better; they reached a level -  that would prevent 41 percent of NTDs.

Neural tube defects (NTDs) are a class of birth defects affecting the brain or spinal cord. They occur in about one per thousand pregnancies in the U.S. each year. Among the most common NTDs are spina bifida, in which a piece of the spinal cord protrudes from the spinal column, causing paralysis below the protrusion, and anencephaly, a fatal condition in which the brain fails to develop normally.

Experts believe that around 50 percent of neural tube defects can be prevented by folic acid and that 200 micrograms a day is a highly effective dose. Previous studies have found that women who take folic acid shortly before and just after they conceive a child are less likely to give birth to a child with an NTD, according to a member of the research team, James L. Mills, MD, Chief of the NICHD’s Pediatric Epidemiology Section.

In addition, the United States Public Health Service currently recommends that all women of childbearing age take a 400 microgram folic acid supplement each day; however, this recommendation is not widely followed. (Folic acid is the form found in vitamin pills; folate is the natural form found in foods.)

Because women are not getting the recommended supplements, the FDA has instituted a program to fortify food with folic acid. By January 1, 1998 , 140 micrograms of folic acid will be added to every 100 grams of grain. This dose should assure an increase of 100 micrograms in the diet of the average woman of childbearing age.

Thus, this study is important for two reasons, Dr. Mills explained. First, it demonstrates for the first time that 100 micrograms will be sufficient to prevent many NTDs. Second, it demonstrates that 200 micrograms will prevent most of the NTDs that are possible to prevent with folate.

Experts have been concerned that, on one hand, the current food fortification plan would not provide enough folic acid to prevent NTDs, and on the other that increasing the level of fortification might not be safe for heavy consumers of grain products. Higher levels of fortification could expose some people to over 1000 micrograms per day. This level could make it difficult to diagnose pernicious anemia in the elderly. Pernicious anemia results from a lack of ability to absorb vitamin B12. Untreated, it can result in severe nerve damage. Doctors often make the diagnosis because of a particular type of anemia; large doses of folic acid can prevent the anemia, making the diagnosis more difficult, while the neurologic damage progresses.

Currently, the National Academy of Sciences’ recommended daily allowance (RDA) for folic acid is 400 micrograms per day for pregnant women and 180 micrograms for other adult women and 200 micrograms for male adults.

Dr. Mills explained that the most definitive way for estimating how much folic acid is needed to prevent NTDs would be to assign women who were trying to conceive a child to one of several groups receiving various doses of folic acid, and to observe how large a dose would be needed to prevent the NTDs. It would be unethical to do this, however, as giving women only a small amount of folic acid might deny them the protection folic acid provides against conceiving a child with an NTD.

Dr. Mills added that earlier studies have measured the folate levels in the red blood cells of both women who have conceived children having an NTD, and of women whose children did not have an NTD. From these measurements, researchers have been able to construct estimates of a woman’s chances of having a child with an NTD, based on her red cell folate levels around the time of conception.

In their study, the Irish and American researchers recruited 100 women of childbearing age and randomly assigned them to receive either a placebo or 100 micrograms, 200 micrograms, or 400 micrograms of folic acid each day for 6 months. Women were not allowed to take part in the study if they were pregnant, planning to become pregnant during the study, or believed that they might soon become pregnant.

At the end of the study period, the researchers measured the folate levels in red blood cell samples the women had provided. Based on these measurements, the women receiving 100 micrograms of folate a day would have decreased their risk of having a child with an NTD by 22 percent, the women receiving 200 micrograms would have a 41 percent decreased risk, and the women in the 400 microgram group would have a 47 percent decreased risk. The researchers added that increasing folate intake by 100 micrograms a day for longer than 6 months could possibly reduce the risk of NTDs by an even greater amount.

Women who have already conceived a child with an NTD are considered to be at high risk for conceiving other children with NTDs. Dr. Mills noted that this study could not assess whether the 100 microgram increase would be effective in reducing the incidence of NTDs born to women in this group, as there were not enough high-risk women available to take part in the study. Such high-risk women should take 4 milligrams (4000 micrograms) of folic acid each day prior to becoming pregnant.