Since 1998, the U.S. has required that grain products be fortified with the B vitamin folic acid to help prevent certain birth defects. Now a new study questions the need for women to get even more folic acid from a pill.
In a study of nearly 6,400 U.S. women who gave birth between 1998 and 2008, researchers found that as the women's intake of folic acid from food rose, there was a steady decline in their risk of having a baby with spina bifida—a serious birth defect of the spine. However, there was no evidence of a further benefit when women took folic acid in pill form—whether in a multivitamin or a single supplement—around the time of conception. The findings "raise the possibility" that in the era of fortified grains, folic acid supplements offer no added protection against spina bifida, Dr. Martha M. Werler and her colleagues at Boston University report in the journal Epidemiology. That would stand in contrast to current recommendations for women of childbearing age. Experts advise them to get 400 micrograms of folic acid per day before conception, as spinal cord defects take shape very early, before many women know they are pregnant. And to get that much folic acid, they would need to take supplements as well as eat fortified foods.
The recommendation is aimed at preventing neural tube defects, severe malformations of the brain and spine. They include spina bifida, where the spine fails to close during early fetal development, and anencephaly, a usually fatal defect where much of the brain never forms. And the current findings should not deter women from taking supplements to get the recommended amount of folic acid, according to a researcher not involved in the study.
"I hope women realize that until more work is done, they should continue to follow this important recommendation to reduce their risk of having a baby with a neural tube defect," Dr. Deborah L. O'Connor, of the University of Toronto and Hospital for Sick Children in Ontario, Canada, said in an email.
In a recent study, O'Connor and her colleagues found that less than 1 percent of Canadian women were able to get the recommended 400 micrograms of folic acid from food alone.
(Canada also requires that folic acid be added to grain products.) A number of studies have found that since the U.S. began requiring folic acid fortification of flours, breads, cereals, pasta and other grain products, rates of neural tube defects have waned. In 2005, according to the Centers for Disease Control and Prevention, about 18 per 100,000 live newborns had spina bifida, the lowest rate ever reported.
For the new study, Werler's team wanted to know whether, in the era of fortified grains, additional folic acid from supplements seems to further cut the risk. They compared 205 mothers who gave birth to a baby with spina bifida between 1998 and 2008, with 6,357 mothers who had a healthy baby. All of the women were asked whether they had used folic acid supplements in the two months before and after conception. They also completed questionnaires on what their diet habits had been before pregnancy. Overall, the researchers found that for every 100 micrograms of folic acid that women consumed from food each day, the risk of having a baby with spina bifida dipped by 13 percent. That included folic acid in fortified grains, as well as folate (the natural form of the B vitamin) in foods like spinach, asparagus, dried beans and peas, and orange juice. However, folic acid from pills was not linked to a benefit.
Overall, 41 percent of the women said they'd used folic acid supplements at least four days per week around the time of conception. But their risk of having a baby with spina bifida was the same as that of women who hadn't used supplements. "Our study findings raise the possibility that supplementation with folic acid during the months immediately preceding neural tube closure does not offer further benefit in reducing the risk of a spina-bifida-affected pregnancy," Werler and her colleagues conclude. There are major caveats, though, the researchers say. One issue is that women were asked to recall their diets and supplement use. It's possible that, knowing folic acid is linked to spina bifida, some women with affected infants said they took supplements when in fact they had not.
O'Connor agreed. "It is very possible that there was recall bias in the study among women who had a baby with a neural tube defect who felt uncomfortable acknowledging they did not regularly consume a folic acid supplement as recommended." It would also be difficult, she noted, for the mothers to accurately recall their pre-pregnancy diets. O'Connor also pointed out that in the early days of fortification, manufacturers added more folic acid to their products than they do now.
"The amount of fortification has come down over the years and is likely to come down further as manufacturers become more comfortable with how much needs to be added to food to meet label claims," she said. The bottom line, according to O'Connor, is that women who might become pregnant should continue to follow current folic acid recommendations.
"As a rule I hope women appreciate they should not discount well-established health recommendations based on a single study," she said. "More work in this area needs to be done."