BALTIMORE » Doctors have long told pregnant women to get enough of the nutrient folate to ensure proper neurodevelopment of their babies, but new research from Johns Hopkins Bloomberg School of Public Health shows that too much also may be a problem.

The research, being presented Wednesday at the International Meeting for Autism Research in Baltimore, found that high levels of folate raise the risk of autism spectrum disorders. More than four times the level considered adequate doubles the autism risk.

High levels of the vitamin B12 may also be harmful, the research found. If both levels are high, a child’s risk for autism increases 17.6 times.

“Adequate supplementation is protective: That’s still the story with folic acid,” said M. Daniele Fallin, one of the study’s senior authors and director of the Bloomberg School’s Wendy Klag Center for Autism and Developmental Disabilities, in a statement. “We have long known that a folate deficiency in pregnant mothers is detrimental to her child’s development. But what this tells us is that excessive amounts may also cause harm. We must aim for optimal levels of this important nutrient.”

Folate is found naturally in fruits and vegetables, and a synthetic version is used to fortify cereals and breads. Many women take a vitamin supplement while pregnant containing folic acid and B12.

One in 68 children in the United States is now believed to have an autism disorder.

The researchers say more research is necessary to determine if women were eating too many fortified foods, taking too many vitamins or had a genetic predisposition to absorbing folate. They also said more study is needed to determine optimal levels.

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