Adding folic acid to foods like cereal and bread 鈥� long considered one of the most successful public health interventions to prevent birth defects 鈥� may be a less effective strategy than once thought, according to a from Stanford University.
In 1998, the U.S. Food and Drug Administration required folic acid, a B-vitamin, to be added to cereal grain products to prevent neural tube defects, which can cause spina bifida, anencephaly, cleft palate and other devastating congenital abnormalities. Major food manufacturers were already adding the vitamin supplement to foods voluntarily two years earlier.
The Stanford researchers examined 1.3 million births and pregnancies over two decades in eight central California counties, and they were surprised by what they found. They knew that neural tube defects in California even before folic acid fortification of food became widespread, though the reasons are unclear.
The researchers anticipated the defects would drop even more sharply after the FDA mandate. That didn鈥檛 happen: the neural tube defects did decline after 1998, but far less sharply than before the fortification started.
鈥淚t wasn鈥檛 what we expected,鈥� said Stanford pediatrics professor Gary Shaw, the study鈥檚 senior author. 鈥淲hat we may be seeing, at least in California in this time period, is that the fortification of foods under the current program has reached its limit in preventing neural tube defects. We don鈥檛 know why. We鈥檙e in a quandary at this point.鈥�
Shaw hopes researchers in other regions will examine local birth data for similar patterns.
The Stanford study isn鈥檛 the first to provide a more nuanced view of the impact of folic acid fortification on reducing birth defects. A concluded that folic acid supplements taken by pregnant women weren鈥檛 enough to prevent some neural tube defects. Public health experts have debated the current required level of folic acid supplementation in food, without reaching a consensus.
The聽U.S. Centers for Disease Control, which sponsored the study, declined to make an expert available for an interview but provided this statement:聽鈥淯nfortunately, even with folic acid fortification, not all women of reproductive age are getting the recommended amount of folic acid, which is 400 micrograms daily. A recent CDC聽聽showed that nearly a quarter of U.S. women of reproductive age (22.8%) did not have enough folate in the blood to prevent neural tube defects. Additional public health interventions targeting these women could help further reduce the number of neural tube defects that occur each year.鈥�
The children of Latinas of neural tube defects, perhaps because the mother鈥檚 diets contain less folic acid, studies have shown. The Central California counties studied by the Stanford researchers have large Hispanic populations, but the researchers did not find significant differences in birth defects between Hispanics and non-Hispanics, Shaw said. He acknowledged, however, that the actual numbers of neural tube defects covered by the study were small. Larger population studies might yield different results.
Neural tube defects, which affect a baby鈥檚 brain or spinal cord, can be devastating and often fatal. They occur in about 3,000 U.S. pregnancies every year.
The defects are caused by the failure of the fetus鈥� neural tube 鈥斅爓hich typically develops into a brain and spinal cord 鈥斅爐o close completely before the end of the first month of pregnancy. That can result in spina bifida, which can leave children paralyzed for life, and anencephaly, in which the brain does not completely develop, usually resulting in death shortly after birth. Researchers still know little about what causes neural tube defects or exactly how folic acid works to prevent them.
Shaw says emphatically that the study鈥檚 results do not suggest folic acid is ineffective. Nationwide, neural tube defects since folic acid fortification started, according to the CDC. The public health intervention has each year, the CDC has reported.
Women of childbearing age should continue to follow federal public health to consume 0.4 mg (400 micrograms) of folic acid daily, in addition to a nutritious diet, Shaw emphasized. Women shouldn鈥檛 wait until they know they are pregnant, because neural tube defects occur within the first month of pregnancy.
Other environmental and cultural factors may be complicating the effects of folic acid fortification in preventing neural tube defects. For example, folic acid fortification starting in the late 1990s coincided with a shift to lower-carbohydrate diets that eschewed the very cereals and bread being fortified.
Obesity among pregnant women also has risen, and the extra weight to a higher risk of neural tube defects. And neural tube defects may be dropping in part because they can be detected through prenatal screening, causing some pregnancies to be terminated.
The Stanford study did examine birth defects that weren鈥檛 originally targeted in the folic acid fortification program but are believed to be affected by it, including cleft lip, cleft palate and gastroschisis 鈥� an increasingly prevalent birth defect in which a baby is born with some of its intestines outside the body. The folic acid intervention seemed to help reduce the proliferation of those defects, Shaw said.
Finally, it鈥檚 possible that some women may not benefit as much as others from folic acid because of their genetic makeup, Shaw noted.
Some experts have questioned whether the required levels of folic acid added to food are adequate, but the FDA isn鈥檛 likely to revisit the issue anytime soon, said Lynn Bailey, a well-known folate researcher at the University of Georgia who was not involved with the Stanford study.
Raising levels much higher could cause unintended health effects. Rather, Bailey suggested, public health experts need to target specific populations, such as Hispanic women, who remain at higher risk for neural tube defects.
鈥淣eural tube defects continue to occur even among those taking vitamin supplements,鈥� Shaw said. 鈥淲e want to identify clues to try to help us understand better ways or additional ways to prevent these birth defects. Have we done everything that we could to prevent neural tube defects? Right now, I鈥檇 say there鈥檚 more to do.鈥�
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