Has folic acid fortification failed?

Debate about the future of folic acid fortification is expected to intensify following a study conducted by the Stanford University School of Medicine, which showed that fortifying the US food supply with folic acid did not achieve the expected decline in certain birth defects.

The study of more than 1.3 million births and pregnancies spanning two decades in California examined neural tube defects (NTDs), which affect a baby’s brain and spine, and which were the intended target of fortification with folic acid, a B vitamin. The research, which has been published online in Birth Defects Research Part A, discovered that NTDs were already becoming less common before fortification began, but that their decline slowed substantially after fortification was introduced.

“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.

Risk factor for birth defects

Lower levels of folic acid intake are known to increase the risk for NTDs, including anencephaly, in which a baby’s brain does not develop, and spina bifida, in which the tube enclosing the spinal cord is open at birth. Anencephaly is usually fatal in the first few days of life, and spina bifida often causes lifelong paralysis.

Because these birth defects occur early in gestation, often before a woman realises she is pregnant, folic acid fortification was introduced in the late 1990s in the US to try to raise everyone’s blood level of the vitamin and thus prevent NTDs. It is now added to cereals, flour and other refined grain products. Natural folates are present in many foods, such as leafy green vegetables, whole grains, citrus fruits and beans.

The study examined pregnancies affected by birth defects from 1989 to 2010. The overall rate of neural tube defects for the entire study period was 87.8 cases per 100,000 births. From 1989 to 1996, before fortification started, NTDs declined by 8.7 cases per 100,000 births per year, for reasons 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 also looked at birth defects that were not originally intended as targets of folate fortification: orofacial clefts, which include cleft lip and palate, and cleft palate alone; and gastroschisis, a birth defect in which a baby is born with some of its intestines outside the body.

After fortification, rates of orofacial clefts decreased by about 2 cases per 100,000 per year. Gastroschisis cases increased for the entire study period, but increased more slowly after fortification.

Ongoing debate

Some experts have suggested that fortification should be increased to prevent more neural tube defects, while others are concerned about the potential side effects of such a change. “An increase in colorectal adenomas has been observed in some countries with folic acid fortification,” Shaw said.

Although the findings may contribute to changes in fortification programs, advice about folic acid for pregnant women and women planning pregnancies remains unchanged. “For women who are planning to become pregnant or are already pregnant, it is still important to take a multivitamin supplement containing folic acid,” Shaw said.