Most bread and cereals in the U.S. are routinely supplemented with folic acid, an essential B vitamin. But that’s not the case in Norway, making the country an ideal locale to examine the effect of folic acid on autism risk.

A new study of more than 85,000 children in Norway suggests folic acid may lower the risk of autism.

Women who took folic acid supplements around the time of conception — from four weeks before pregnancy to eight weeks into pregnancy — had nearly half the risk of having a child with autism than women who did not take the supplements, according to the study.

Taking folic acid during pregnancy is known to reduce the baby’s risk of neural tube defects, such as spina bifida, and public health agencies in the U.S. recommend that women trying to get pregnant take 400 micrograms of the vitamin per day.

Studies have suggested that folic acid reduces the risk of autism as well.

A small study published last year found that mothers of typically developing children are much more likely to have taken folic acid in the first month of pregnancy than are mothers of children with autism. The effect is strongest in women with mutations in the enzyme methylenetetrahydrofolate reductase (MTHFR), which catalyzes a reaction converting one form of
folic acid to another.

The strength of the new study is that it is prospective, or forward-looking, meaning that women were enrolled in the study near the beginning of their pregnancies, and recorded their supplement use throughout. That is generally considered more reliable than retrospective studies, in which scientists ask participants to recall past behavior.

Low prevalence

Still, researchers caution that the findings need to be confirmed in other groups.

At the end of the study, 270 of the 85,000 children had been diagnosed with autism. That’s a lower overall prevalence — about 0.3 percent — than has been reported in the U.S., where autism rates are estimated to be 1.1 percent.

The reason for this difference is not clear, though at about 0.8 percent, overall autism prevalence in Norway is also lower than in the U.S. At the end of the study period, the children ranged in age from about 3 to 10 years, so it’s possible that the prevalence in the study will rise as the younger children get older.

As the authors note, it’s possible that other factors contributed to the finding. The women in the study weren’t assigned to take folic acid, and researchers merely recorded their natural behavior. Further analysis revealed that those who take folic acid tend to have a higher socioeconomic status and more health-conscious behavior in general than those who don’t.

But researchers say they don’t think this made a substantial difference. Fish oil supplements, which are also more commonly taken by wealthier women, do not appear to have the same benefit, nor does folic acid use later in pregnancy. Neither maternal psychiatric disorders nor medication use seem to play a role, either.

Folic acid plays many roles in the body, including DNA synthesis and chemical modifications of DNA, and it’s not yet clear how it might reduce the risk of autism. Its role in chemically altering DNA may be of particular interest to scientists
studying autism as interest grows in epigenetics, the chemical modifications that alter gene expression without
changing the DNA sequence.