From the moment a woman learns she is pregnant, her lifestyle, diet, and future changes. She tends to eat more, cut out alcohol, and keep in mind all of her nutrition needs to ensure her baby’s healthy development. The American Pregnancy Association encourages expectant mothers to eat a healthy variety of foods and pay special attention to how much folic acid they consume, a vitamin that increases blood flow and plays a key role in forming the spine of a fetus.

But according to a new set of findings, scheduled to be presented at the International Meeting for Autism Research, too much folate may backfire for mothers with good intentions by increasing the odds their child will develop autism.

For the study, a research team from Johns Hopkins School of Medicine analyzed data from 1,391 mother-child pairs who were mostly low-income, minority populations from the Boston area. From the time of the birth, between 1998 and 2013, researchers followed the children for 15 years to see whether or not they had developed normally. They measured the mother’s blood for her folate levels within one to three days of delivery and found 10 percent of the women had excess folate in their system and another 6 percent had too much vitamin B12.

It’s unclear why these levels were high since most of the mothers reported taking no more than the recommended dose of multivitamins throughout their pregnancy. The researchers questioned whether the combination of folate-laden food and supplements allowed women to absorb too much, or if some absorb folate better than others because of their genetic makeup.

Women who had high levels of folate were more likely to give birth to a child who would later be diagnosed with autism spectrum disorder (ASD), a developmental brain disorder that causes social, cognitive, and communication impairments that can range from very mild to very severe. But the evidence is extremely premature and researchers need to investigate further before making a definitive link between mothers who overdosed on folate during pregnancy and ASD.

"This research suggests that this could be the case of too much of a good thing," said the study’s lead author Ramkripa Raghavan, a researcher at the Department of Population, Family and Reproductive Health at the Bloomberg School, in a statement. "We tell women to be sure to get folate early in pregnancy. What we need to figure out now is whether there should be additional recommendations about just what an optimal dose is throughout pregnancy."

Folate is a B-vitamin that’s found in a variety of healthy food sources. A form of folate, known as folic acid, can be consumed in dietary supplements and added to foods (fortified). According to The National Institutes of Health Office of Dietary Supplements, women and teenage girls who could become pregnant should consume around 400 micrograms (mcg) of dietary folate or folic acid from supplements. While folate can be found naturally in certain breads, cereals, and pastas, it’s recommended to include a range of fruits and vegetables that not only supply folate, but are also packed with vitamins and minerals.

Folate food sources include vegetables, such as asparagus, brussel sprouts, and dark leafy vegetables like spinach and kale; fruits, such as oranges; and nuts, beans, and peas, such as peanuts, black-eyed peas, and kidney beans. There are prenatal dietary supplements that include the adequate amount of folic acid, but B-complex dietary supplements also provide an adequate dose.

"Adequate supplementation is protective: That's still the story with folic acid," explained one of the study's senior authors M. Daniele Fallin, director of the Bloomberg School's Center for Autism and Developmental Disabilities, in a statement. "We have long known that a folate deficiency in pregnant mothers is detrimental to her child's development. But what this tells us is that excessive amounts may also cause harm. We must aim for optimal levels of this important nutrient."

Women who fail to include enough folate in their body may experience megaloblastic anemia, which causes weakness, fatigue, trouble concentrating, irritability, headache, heart palpitations, and shortness of breath. But for women who are pregnant, not enough folate in their diets affects their baby’s risk for developmental problems. Newborns may be born premature or with a low birth weight and in serious cases they may develop neural tube defects, such as spina bifida.

“We see this as evidence that there is a subset of people for whom excessively high levels of folate might be at risk for autism [in their children],” Fallin said in an interview with The Atlantic. However, she warns: “There's this danger that the message would be that folate supplementation is bad. And that's not at all what we saw.”

Source: Fallin MD and Raghavan R. International Meeting for Autism Research . 2016.