A study suggests that children whose mothers took folic acid supplements before and during pregnancy may be significantly less likely to develop autism.
Women who take the recommended amount of folic acid (vitamin B9) before and in the early stages of pregnancy may be up to 40 per cent less likely to have a child with autism, scientists have found.
Researchers in Norway and the US looked at data from the Norwegian Mother and Child Cohort Study and the Autism Birth Cohort (ABC) Study.
These provided them with data on more than 85,000 babies that were born between 2002 and 2008, as well as their mothers' prenatal dietary habits.
Analysis revealed that 270 cases of autism spectrum disorder (ASD) were diagnosed among the children, including 114 cases of autistic disorder, 56 of Asperger syndrome and 100 of atypical or unspecified autism.
Women who took folic acid supplements in early pregnancy were found to have a 40 per cent reduced risk of having a child with autism than those who did not take supplements.
The supplements had to be taken from four weeks before conception to eight weeks after the start of pregnancy to be effective.
However, folic acid supplementation did not reduce the risk of atypical or unspecified autism and the researchers could not draw firm conclusions about Asperger syndrome as there were not enough children with the disorder in the study group.
The findings are published in the Journal of the American Medical Association and suggest that prenatal supplementation with folic acid - which is already known to reduce the risk of neural tube defects such as spina bifida - could help to reduce the risk of autism among children.
Ezra Susser, joint senior author at Columbia University, claimed that folic acid supplementation could be an "important and inexpensive public health initiative" for reducing the risk of ASDs.
Folic acid in its natural state, folate, can also be obtained from dietary sources, such as leafy green vegetables, peas, lentils, beans, eggs, yeast and liver.