Researchers at University of California, Davis in the US found that children whose mothers took 800 or more microgrammes of folic acid had a significantly lower risk of developing autism spectrum disorder (ASD) - even when their mothers were exposed to household or agricultural pesticides associated with increased risk.
They found that mothers who took less than 800 microgrammes and encountered household pesticides had a much higher estimated risk of having a child who developed an ASD than moms who took 800 microgrammes of folic acid or more and were not exposed to pesticides.
"We found that if the mom was taking folic acid during the window around conception, the risk associated with pesticides seemed to be attenuated," said Rebecca J Schmidt, assistant professor at University of California.
"Folic acid intake below the median and exposure to pesticides was associated with higher risk of autism than either low intake or exposure alone. The mothers who had the highest risk were the ones who were exposed to pesticides regularly," Schmidt added.
Mothers were interviewed about their household pesticide exposure during pregnancy, as well as their folic acid and B vitamin intake.
The study was published in the journal Environmental Health Perspectives.