Researchers in Norway looked at data from 85,000 pregnancies, and found that women who took the supplement four weeks before pregnancy, and through the eighth week of pregnancy, were 39% less likely to have children with autism.
The Norwegian study is the largest to date on the benefits of folic acid for autism prevention, and marks one of the first tangible things a woman can do to reduce her risk of giving birth to a child with the disorder.
"This is pretty exciting," said Alycia Halladay, senior director for environmental and clinical sciences for Autism Speaks, an autism advocacy group. "It actually supports the idea of actionable things women can do before they become pregnant, and right as conception happens."
Experts have known for some time that taking folic acid can prevent neural tube birth defects like spina bifida in developing fetuses. American Congress of Obstetricians and Gynecologists (ACOG) guidelines call for all women of child-bearing age - not just those who plan to get pregnant - to take 400 micrograms of folic acid daily to prevent birth defects. The same dose appears to provide some benefit in preventing autism, according to the research.
The study supports earlier research from 2012 that found that women who take prenatal vitamins--which are rich in folic acid--also lower their babies' autism risk by as much as 40 percent.
Image: Pregnant woman taking supplements, via Shutterstock