Whether certain supplements, taken before or during pregnancy, can reduce the risk of autism is a hotly debated question. A new large-scale study takes a fresh look.

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Could taking supplements during pregnancy reduce autism risk?

Autistic spectrum disorders (ASDs) are believed to affect 1 in 68 children in the United States, and their prevalence may be on the rise.

Despite this, the exact causes and risk factors involved are still shrouded in mystery. No one knows why ASDs occur and how they can be prevented.

Over the years, several studies have looked at the links between a mother’s nutritional status and the cognitive abilities of her offspring. The findings, to date, have been inconclusive, but scientists believe that this line of questioning might eventually help to solve the ASD riddle.

For instance, previous work has shown a relationship between low maternal vitamin D and ASD. Similarly, neural tube defects — that is, birth defects of the brain, spine, or spinal cord that occur very early in pregnancy — are known to be prevented by increased folic acid intake.

For these reasons and others, pregnant women are recommended to take multivitamins and folic acid supplements as standard.

Because relationships between multivitamin and folic acid supplementation and ASDs have been inconsistent, a study published this week in JAMAreopens the question.

The current research team was headed up by Stephen Z. Levine, Ph.D., of the University of Haifa, Israel. Data were taken from 45,300 Israeli children born 2003–2007 who were followed up until 2015.

The scientists gathered information about any prescription supplements taken by the mothers before pregnancy (540–271 days before childbirth) and during pregnancy (270 days before childbirth up to childbirth).

Of the 45,300 children born to 26,702 mothers, 572 were diagnosed with ASD.

The authors concluded that there was a decreased risk of the offspring developing ASD if the mothers took folic acid, multivitamin supplements, or both either before pregnancy, during pregnancy, or both before and during.

To reiterate, supplements taken before pregnancy began, during pregnancy, or both before and during appeared to reduce the risk of ASD in the offspring.

This positive effect remained significant after a range of confounding variables were accounted for. The protective effect was measured in both male and female offspring, but the authors note that the low number of ASD diagnoses in females makes this conclusion less firm.

Among the children of women with psychiatric conditions, the risk of ASD did not diminish with supplementation, although, again, the sample size was relatively small.

The new results back up earlier conclusions from a Norwegian study that found that maternal folic acid use from 4 weeks before and 8 weeks into pregnancy was associated with a reduced risk of ASD. But although the findings are in line with some previous studies, not all previous research found such an effect.

This current study also marks the first time that links that go back further in time have been found: supplement use 2 years before pregnancy reduced ASD risk. That said, the authors are quick to describe the new experiment’s limitations, which include the lack of a sibling control analysis.

Additionally, information regarding supplement use came from prescription records. It is therefore possible that some mothers bought over-the-counter supplements, which would not have been included in the analysis.

The study is only observational, meaning that a causal relationship cannot be proven. Further studies will be needed to understand whether or not this anti-ASD effect is real.

The authors write in their conclusion, “Reduced risk of ASD in offspring is a consideration for public health policy that may be realized by extended use of [folic acid] and multivitamin supplements during pregnancy.”

Whether the results are replicated or not, advice to pregnant mothers will remain unchanged: multivitamin and folate supplementation will be recommended, regardless.

Hopefully, in time, any nutritional components of ASD risk will be pinned down once and for all.