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NEW YORK - Doctors advise pregnant women to take 400milligramsof folic acid every day. It's a proven method of reducing their baby's risk for serious birth defects, like spina bifida. Now, however, there may be an added benefit.

"If you're on folic acid, you may reduce the chance of having a child with autism," Dr. Max Wiznitzer with UH Rainbow Babies and Children's Hospital said.

Researchers in Norway followed 85,000 children for six years. They found women who took folic acid supplements before they got pregnant and during the first trimester lowered their risk of developing autism by 40 percent.

Experts in the field call this link between nutrition and autism a landmark finding. But, it's just one piece of a complicated puzzle of genetic and environmental factors that influence autism development.

"This does not prevent autism. There were women in this study who took prenatal folic acid and went on to have a child affected with autism," Dr. Alycia Halladay with Autism Speaks said.

Our food supply is fortified with folic acid, but experts say many women may not be getting enough in their diet to make a difference. They say there is no downside to taking the supplements.

"To me, this is a no-brainer. It's a win-win proposition. It's good for the mother, it's good for the fetus, and you can't ask for anything better than that," Dr. Wiznitzer said.

In addition to supplements and fortified breads and cereals, folic acid is found naturally in dark green, leafy vegetables.