Prenatal Vitamins Linked To Autism, But Don’t Freak Out Quite Yet

Moms-to-be, keep taking your folic acid

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May 12, 2016 at 1:58 PM ET

Expectant mothers are given lots of advice to ensure the health of their babies: don’t drink alcohol, get enough exercise, limit your intake of high-mercury fish. One of the biggest no-brainers is to take prenatal vitamins, which contain folic acid, the man-made version of a nutrient called folate that the body uses during cell division and to construct DNA.

Now researchers from Johns Hopkins University have conducted a cohort study that has reached a disturbing conclusion: Pregnant women who had very high folate levels during pregnancy were 17 times more likely to have a child with autism.

These results are disturbing and provocative. But this one study isn’t reason enough to throw decades of scientific research out the window.

Everyone needs some folate. It’s found naturally in a number of foods, such as fruits, vegetables, and nuts, and is added to a grain-based foods including pasta, cereal, and masa flour used in tortillas. But pregnant women need more of it, about 50 percent more every day than people ages 14 and up, according to the National Institutes of Health.

Up until now, there hasn’t been any scientific evidence that high levels of folate are detrimental to fetuses at all. In fact, low folate levels have been associated with neural tube defects, severe birth defects that include anencephaly and spina bifida.

On its face, the study looks strong. The researchers looked at a large cohort of nearly 1,400 pairs of mothers and children. They correlated the mothers’ levels of plasma folate, a proxy measurement for the overall amount of folate in their bodies, shortly after delivery with the children that had been later diagnosed with autism.

But there’s something a little strange with the group of study participants, says Sarbattama Sen, a professor of pediatrics at Tufts University who recently presented a similar paper about the role of folates and came to the opposite conclusion. “I don’t have a great description of this cohort, but seems to have a very high rate of Autism Spectrum Disorder,” she says. Nationally, autism occurs in one out of every 68 people, but in this study, it’s in one in 12. That’s about four times the national rate, Sen adds. To further confuse matters, the cohort included a higher proportion of lower-income minorities than is representative of the national population, but, typically, autism is more commonly diagnosed in white populations.

There are lots of reasons, too, that women might have high folate levels—it might not come from taking too many prenatal vitamins. Genetic mutations that can affect how the body absorbs folates, which would have thrown off the measurement of folate metabolites that the researchers looked at. Though they corrected for one mutation in their analysis of the data, Sen doesn’t think they looked at any others.

The study authors themselves have noted that they want to redo their study with a larger sample size and a different cohort. And they insist that expectant mothers should keep taking their prenatal vitamins—it’s only extremely high levels that were shown to be detrimental, and the mechanism that might be causing it is still a mystery. And after all, this is just one study.

“This is the first study that has had any kind of association between adverse outcomes and high [folate] levels…the reason for recommending folates goes beyond what this research shows,” Sen says. “At this point, this study should not at all guide our clinical practice.”