By Stephanie Stahl

PHILADELPHIA (CBS) — Reducing the risk of autism with a popular vitamin. New research out is generating a lot of excitement. Health Reporter Stephanie Stahl explains the discovery.

Folic acid can reduce the risk of autism, that’s according to the large new study. It’s a b-vitamin that pregnant woman are already advised to take, and now it could have another benefit.

Danesha Smith is 11 weeks pregnant with her second child, and is taking the recommended multivitamin with folic acid.

“We put a lot of focus on healthiness, being healthy, taking the right vitamins, eating well,” said Danesha.

The new research shows mothers like Danesha, who took folic acid supplements before they conceived and during the first two months of their pregnancy, lowered their chances of having a child with autism by 39 percent.

“It’s exciting news; anything that comes out that has potential for reducing the risk or unraveling the mystery of autism is exciting,” said Dr. Jared Caruso, a Pediatrician with Main Line Health.

He says folic acid is already known to reduce the risk of a variety of neurological and spinal disorders, including spina bifida.

“This vitamin is important in the developing the brain,” said Dr. Caruso.

The new study in the Journal of the American Medical Association looked at 85,000 children in Norway.

“It will lead to new ideas and potentially new ways to prevent autistic disorders,” said Dr. Robert Berry, with the Centers for Disease Control and Prevention.

But the research didn’t explain how folic acid reduces the risk of autism.

The new study says timing is especially important. The autism risk was only reduced when a mother took folic acid right before and after getting pregnant.

Folic acid is found in foods, including leafy vegetables, citrus fruits and whole grains. But most women do not get enough through food alone.