Prenatal vitamins reduce the risk of autism by half, even more for some higher-risk cases

Women who reported not taking prenatal vitamins immediately before and during a pregnancy were twice as likley to have a child with autism, UC Davis researchers reported Wednesday. If the women also had a mutation in a high-risk gene, they were seven times as likely to have a child with the developmental disorder, the researchers reported in the online edition of the journal Epidemiology. The study is scheduled to appear in print in July.

Epidemiologist Rebecca J. Schmidt of the UC Davis MIND Institute and her colleagues studied about 700 Northern California families with 2- to 5-year-old children with autism who were participants in the Childhood Autism Risk from Genetics and the Environment study from January 2003 to December 2009. In telephone interviews, the mothers were asked whether and when they took prenatal vitamins and the type of vitamins ingested.

The team found that mothers who took the vitamins prenatally or during the first month of pregnancy were only half as likely to have a child with autism as those who didn’t. For mothers who began taking them in the second month of pregnancy, there was no effect, however. This suggests that by the time most women learn they are pregnant, beginning to take the vitamins will provide little or no benefit in terms of autism.

The researchers also found strong associations with two gene mutations that had previously been linked to autism risk. One is the variant of the methylenetetrahydrofolate reductase (MTHFR) gene associated with less efficient metabolism of folic acid and increased blood levels of the amino acid homocysteine.The other was a variant of the catechol-O-methyltransferase (COMT) gene, which is also linked to increased levels of homocysteine. For women who did not take vitamins and had the MTHFR variant, the risk of having an autistic child was 4.5 times normal. For those who did not take vitamins and had the COMT variant, the risk was seven times normal.

“The good news is that, if this finding is replicated, it will provide an inexpensive, realtively 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 a pregnancy,” said epidemiologist Irva Hertz-Picciotto, the senior author of the study. It is important to replicate it, she added, because the study relied on women’s recall of their vitamin use, which is not always accurate.