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New Stanford study raises questions about effect of folic acid supplementation on birth defects

CerealFor nearly two decades, the U.S. food supply has been fortified with folic acid to try to prevent birth defects that affect babies' brains and spines. But the fortification program may not be having the intended effect, according to a Stanford study published today in Birth Defects Research Part A.

Folic acid is a B vitamin that is added to cereals, flour and other refined grain products as part of a public health effort to prevent neural tube defects. If you've been pregnant in the last 20 years, your doctor probably encouraged you to take a prenatal multivitamin supplement that included folic acid, and to eat plenty of foods that contain natural folates, such as leafy greens, citrus fruits and beans. Those recommendations were based on research demonstrating that women with low folate levels are at risk for pregnancies affected by anencephaly, in which the baby's brain does not develop properly, and spina bifida, in which the tube around the spine doesn't close correctly.

Since neural tube defects occur very early in pregnancy, before most women even realize they are pregnant, the fortification program was introduced in the late 1990s to try to provide another avenue for prevention. Rates of neural tube defects have indeed declined since the introduction of fortification, but that statistic doesn't tell the whole story, according to the new study of 1.3 million California births and pregnancies. From our press release:

Neural tube defects were already becoming less common before fortification began, and their decline slowed substantially after fortification was introduced, the study found.

“We did not see what we would have expected to see, and that’s a concern,” said the study’s senior author, Gary Shaw, PhD, professor of pediatrics at Stanford.


From 1989 to 1996, before fortification started, NTDs declined by 8.7 cases per 100,000 births per year.

“The downward trend in neural tube defects started probably in the late 1960s or early 1970s; it was happening even before folic acid was likely added to multivitamin supplements or certain foods,” Shaw said. The reason for the pre-fortification decline is unknown.

However, after fortification was fully implemented, between 1999 and 2010, NTDs declined more slowly, by 1.7 cases per 100,000 births per year, the study found.

The study does not exclude the possibility that changes in the rate of birth defects were due something else besides folic acid fortification that changed at the same time. For instance, the researchers note that maternal obesity rates rose during the study period, and this change may have affected the rate of birth defects. Still, the new data will likely contribute to an ongoing debate about whether the fortification program should be modified in the future.

It's important to note that the findings don't change the standard advice for pregnant women and those who want to become pregnant, Shaw said: They should still take a multivitamin that includes folic acid. The March of Dimes website has a good explanation of current supplement recommendations.

Previously: Birth defects linked to air pollution in new Stanford study, Better diet in pregnancy protects against birth defects and Hoping to end hidden hunger through food fortification
Photo by musicfanatic29

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