Women who do not take prenatal vitamins early in their pregnancy are twice as likely to have a child with an autism spectrum disorder than those who do, says a new study.
It found that for women with a particular high-risk genetic makeup who reported not taking prenatal vitamins, the estimated risk of having a child with autism was as much as seven times greater than in women who did report taking prenatal vitamins and who had more favorable gene variants.
"Mothers of children with autism were significantly less likely than those of typically developing children to report having taken prenatal vitamins during the three months before and the first month of pregnancy," said lead researcher Rebecca J. Schmidt, assistant professor in the Department of Public Health Sciences in the UC Davis School of Medicine.
The finding was strong and robust, and is the first to suggest a concrete step women can take that may reduce the risk of having a child with autism.
The researchers postulate that folic acid, the synthetic form of folate or vitamin B9, and the other B vitamins in prenatal supplements, likely protect against deficits in early fetal brain development.
Folate is known to be critical to neurodevelopment and studies have found that supplemental folic acid has the potential to prevent up to 70 percent of neural tube defects, said the authors.
"This finding appears to be the first example of gene-environment interaction in autism," said senior author Irva Hertz-Picciotto.
"It is widely accepted that autism spectrum disorders are the result of multiple factors, that it would be extremely rare to find someone who had a single cause for this behavioral syndrome. Nevertheless, previous work on genes has generally ignored the possibility that genes may act in concert with environmental exposures," said Hertz-Picciotto.
The finding, if replicated, provides a potential means of reducing the risk of having a child with autism, said the researchers.
"The good news is that if this finding is replicated, it will provide an inexpensive, relatively simple evidence-based action that women can take to reduce risks for their child, which is to take prenatal vitamins as early as possible in a pregnancy and even when planning for pregnancy," said Hertz-Picciotto.
The study is published online in the journal Epidemiology and will appear in print in July.