Some preliminary findings presented this week at a meeting of autism researchers may have mothers-to-be fretting about their prenatal vitamins.
The blockbuster statistic that sent tongues wagging was this: Women who got too much folate and vitamin B12 during pregnancy were 17.6 times more likely to have their children diagnosed with an autism spectrum disorder.
That figure may sound shockingly high, but it's not a typo: Compared with mothers who had normal levels of folate and vitamin B12, those who had elevated levels of both vitamins saw their children's risk of autism surge by a factor of 17.6.
At first glance, the message seems clear: Think twice before taking prenatal vitamins.
But that take-away is actually contrary to the study's findings.
The research was conducted by a team from Johns Hopkins University. They analyzed data from 1,391 mothers and their children who participated in the Boston Birth Cohort, a project aimed at understanding the roots of developmental diseases. Volunteer pairs were recruited when the children were born and then tracked for up to 15 years.
All of the mothers took surveys about their use of prenatal vitamins and other supplements throughout their pregnancies. The women also gave blood samples within three days of giving birth, allowing researchers to measure levels of prenatal vitamins in their systems at the end of their pregnancies.
Medical records showed that 107 of the 1,391 children were diagnosed with an autism spectrum disorder. But the risk of a diagnosis was not spread evenly among all mother-child pairs.
For instance, mothers who said they took prenatal multivitamins three to five times per week were much less likely to be told that their child was on the autism spectrum compared with mothers who didn't take the vitamins. Those who used them in the first trimester were 67% less likely to have a child with autism; those who used in them in the second trimester were 62% less likely to get that diagnosis; and those who used them in the third trimester were 57% less likely to wind up with an affected child, the researchers reported.
But here's the part that has some people wondering whether they should lay off the vitamins instead: When the researchers focused on two specific vitamins – B12 and folate – they noticed that too much supplementation might backfire.
Among the 1,391 mothers, 95 had blood levels of B12 that were considered excessive by the World Health Organization. And among these mothers, 15 had children who were diagnosed with an autism spectrum disorder, a risk that was three times higher than for the other mothers.
Similarly, 140 of the mothers had "excess" levels of folate in their blood, and 16 of them had children who developed an autism spectrum disorder. That meant their risk was a little more than double that of the other mothers.
Most striking were the 21 mothers who had "excess" levels of both vitamins. In this group, 10 had children who were diagnosed with autism. That's nearly half, noted Ramkripa Raghavan, lead author of the report.
After accounting for other factors that might influence the chances of developing autism, the researchers calculated that being exposed to too much folate and too much B12 was associated with a risk that was 17.6 times greater than for children whose mothers had "normal" levels of both vitamins.
Folate is an essential vitamin that allows cells to divide and DNA to be constructed, according to the National Institutes of Health's Office of Dietary Supplements. It's particularly important for pregnant women – those who are deficient put their babies at risk of developing spina bifida and other neural tube defects. That's why the Food and Drug Administration requires breads and many other grain-based foods to be fortified with folic acid, a type of folate.
Vitamin B12 also plays a crucial role in DNA synthesis and neurological function, among other necessary biological tasks, according to the Office of Dietary Supplements.
It's not clear why some of the women in the study – an "inner city, minority" population that is 65% African American and 25% Latina – had such high levels of folate and B12. It's possible that they overdid it with their supplements, or that their bodies naturally absorb more of these vitamins or metabolize them more slowly, Fallin told ResearchGate. The team members plan to look for answers to this question, she said.
They will also try to replicate these findings, she added, perhaps in other groups of women with different health histories.
In the meantime, the scary-sounding link between vitamins and autism is not the thing to focus on. As the researchers themselves reported in April, "maternal vitamin supplementation was protective" against the risk of autism spectrum disorders.
And yet the potential dangers have dominated the conversation.
Dr. James Hamblin, an editor at the Atlantic, wrote that the publicity could derail efforts to improve widespread folate supplementation and further reduce the risk of neural tube defects. The science behind this policy is not in doubt.
On the other hand, the evidence linking excess folate and B12 on the one hand and autism on the other "is extremely premature," he wrote. The data must be scrutinized by other scientists, then confirmed by independent researchers. Only after a lot more work could the link "reliably be said to exist," he wrote.