The incidence of autism has been growing at an alarming rate but the cause of the disorder has been unclear. However, a new study finds that folic acid supplements taken by the mother may provide some protection for the developing fetus.
The study, appearing in the February 13 issue of JAMA, included about  85,000 Norwegian children. It found that maternal use of supplemental folic acid from 4 weeks before to 8 weeks after the start of pregnancy was associated with a lower risk of autistic disorder in children.
The apparent benefit that was found in early pregnancy was not, however, present for folic acid use in mid-pregnancy.
"Our main finding was that maternal use of folic acid supplements around the time of conception was associated with a lower risk of autistic disorder," the researchers said. "This finding does not establish a causal relation between folic acid use and autistic disorder but provides a rationale for replicating the analyses in other study samples and further investigating genetic factors and other biological mechanisms that may explain the inverse association."Â
Folic acid supplementation has long been recommended for use around the time of conception because of evidence that it reduces the risk of neural tube defects in children.
This protective effect has led to mandatory fortification of flour with folic acid in several countries, and it is generally recommended that women planning to become pregnant take a daily supplement of folic acid starting one month before conception.
Study detailsÂ
Pal Surén, M.D., M.P.H., of the Norwegian Institute of Public Health, Oslo, and colleagues conducted the stsudy, which used a sample of 85,176 children was derived from the population-based, prospective Norwegian Mother and Child Cohort Study (MoBa).
A total of 270 children (0.32 percent) in the study sample have been diagnosed with autism spectrum disorders (ASDs): 114 (0.13 percent) with autistic disorder, 56 (0.07 percent) with Asperger syndrome, and 100 (0.12 percent) with pervasive developmental disorder-not otherwise specified (PDD-NOS).
The researchers found that there was an inverse association between folic acid use and subsequent risk of autistic disorder. Autistic disorder was present in 0.10 percent (64/61,042) of children whose mothers took folic acid, compared with 0.21 percent (50/24,134) in children whose mothers did not take folic acid, representing a 39 percent lower odds of autistic disorder in children of folic acid users.
Characteristics of women who used folic acid within the exposure interval included being more likely to have college- or university-level education, to have planned the pregnancy, to be nonsmokers, to have a pre-pregnancy body mass index below 25, and to be first-time mothers.
"No association was found with Asperger syndrome or PDD-NOS, but power was limited. Similar analyses for prenatal fish oil supplements showed no such association with autistic disorder, even though fish oil use was associated with the same maternal characteristics as folic acid use," the authors write.
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