Mothers who take folic acid supplements in early pregnancy are 40% less likely to have children with autistic disorders, a new study shows.
The findings have been published by Norwegian researchers in the Journal of the American Medical Association and are based on a study of 85,176 children.
However, the authors warn they have not yet conclusively proved that folic acid is behind the risk reduction and further research is needed.
Researchers found about one in a 1000 mothers who took folic acid supplements had a child with an autistic spectrum disorder, compared with about two in 1000 of mothers who didn't.
Folic acid has already been shown to reduce the risk of neural tube defects such as spina bifida.
More than 50 countries, including the United States and Canada, legally require bakers to add the B vitamin to bread.
However, the New Zealand government decided last year not introduce mandatory folic acid fortification of bread.
Autism New Zealand says the research is very interesting but wants to see the findings replicated by studies of children in other countries.