Doctors have long told pregnant women to get enough of the nutrient folate to ensure proper brain development in their babies, spurring widespread use of prenatal vitamins as well as fortified foods and a decrease in the incidents of certain birth defects.
New research, however, suggests there can be too much of a good thing.
A small study from the Johns Hopkins Bloomberg School of Public Health found that excessive folate levels as well as high levels of vitamin B12 in mothers appear to raise the risk of autism spectrum disorders in children.
The findings surprised researchers because folate is thought to stave off autism, said M. Daniele Fallin, a senior study author and director of the Johns Hopkins’ Wendy Klag Center for Autism and Developmental Disabilities. Proper levels of folate, also a B vitamin, are still widely believed to be protective, she said.
“We certainly don’t want women to stop taking their vitamins or restrict their diets,” Fallin said after presenting the findings at the International Meeting for Autism Research in Baltimore. “We’re talking about excessive amounts.”
An excessive amount is more than four times the level considered sufficient. The Centers for Disease Control urges women to get 400 micrograms a day, beginning at least one month before getting pregnant to stave off birth defects of the brain and spine, in addition to autism. The vitamin is used to help the body make new cells and promotes neurodevelopmental growth.
Often called folic acid in supplements, folate is found in fruits and vegetables, particularly dark leafy greens, as well as nuts, beans, dairy products and meats. In 1998, the U.S. Food And Drug Administration began requiring manufacturers to enrich breads, cereals and pastas with folic acid, a move that government data shows increased intake by 190 micrograms a day.
The increased consumption of folate was considered a major public health success.
What isn’t clear is why some women got too much, Fallin said. The study checked the folate levels in the blood of nearly 1,400 low-income minority women in Boston just after they gave birth and then followed the children for years.
Ten percent of those women had excessive levels of the vitamin and they were twice as likely to have a child with autism than those with normal folate levels.
Fallin said a majority of the 1,400 women reported taking multivitamins throughout pregnancy. The women with excessive levels may have over-supplemented with vitamins or could have a genetic predisposition that causes them to metabolize the vitamin more slowly or absorb greater quantities, or a combination of both.
The Hopkins study is unlikely to change doctors recommendations about the need for folate. The American College of Obstetricians and Gynecologists recommends pregnant women take a supplement during pregnancy and childbearing years.
“It’s pretty much the only supplement that we specifically recommend,” said Kate Connors, a spokeswoman for the doctors’ organization. “We wouldn’t plan to change our recommendations based on just one small study, since a lot of evidence points to the value of folic acid. Moreover, we would not want to scare women away from folic acid, which is very important at preventing neural tube defects.”
Despite the decades-long push to get women of reproductive age to consume more folate, some women still don’t get enough. One in four women of reproductive age are deficient, according to the U.S. Centers for Disease Control and Prevention.
But most women seem to have gotten the message. By 2007, the CDC found that 40 percent of women of childbearing age reported taking folic acid daily and 81 percent said they were aware of it.
There are about 3,000 cases annually in the United States of the most common neural tube defects, spina bifida or anancephaly, caused by incomplete closing of the spine and skull. That’s down from about 4,100 cases before folic acid fortification of breads and cereals. The number of deaths each year due to neural tube defects also dropped to 840 annually after fortification from about 1,200 before.
About one in 68 children in the United States has an autism spectrum disorder, and researchers still struggle to identify the causes though they suspect both genetic and environmental factors. The condition leads to social impairment, abnormal communication and repetitive behavior.
Fallin’s study also found a higher risk of autism for babies born to women with high levels of the vitamin B12, for which there isn’t a well established threshold for what’s considered adequate. Those women were three times as likely to have an autistic child. High levels of both increased the risk by more than 17 times.
Both Fallin and others who support autism research agreed more study is needed before there are any changes to folate recommendations.
“This research is interesting but preliminary; the numbers of women in the study are relatively small and this really does need to be examined more in a bigger population before anyone is making any recommendations,” said Paul Wang, senior vice president of medical research for the advocacy group Autism Speaks. “At this point, and I think the authors of the study would agree, women should still be following the current recommendations on folate. There’s no reason to exceed them. Some people think they should take super doses of this or that, but there’s never been evidence that’s helpful.”
At least one autism researcher at Wednesday’s conference, due to deliver her second child in July, said she won’t stop taking her folate supplement.
“There are a lot of things to stress about when you’re pregnant,” said Carissa Cascio, an associate professor of psychology at Vanderbilt University. “I’ll keep taking my vitamin.”