New Studies of Air Pollution, Pesticides and Iron Bolster Evidence Tying Developmental Disorder to Influences in Womb
SAN SEBASTIÁN, Spain—Researchers at an international conference on autism Friday presented three new studies lending strength to the notion that environmental influences before birth play a role in the risk for the condition.
In one study, pregnant women who were exposed to certain levels of air pollution were at increased risk of having a child with autism. Another presentation suggested that iron supplements before and early in pregnancy may lower the risk, and a third suggested some association between use of various household insecticides and a higher risk of autism.
The causes of autism, a developmental disorder that involves social-skill problems, among other symptoms, aren’t well understood but are thought to be multifaceted. Genetics likely account for about 35% to 60% of the risk, many researchers say. But some experts and parents believe that nutrition and other environmental factors may also play a role, especially as the rate of autism in the U.S. appears to have climbed sharply over the past decade.
The new studies showed only associations and couldn’t prove causality, and each factor itself likely accounts for a small portion of the risk for autism, researchers say. But the results, taken together with previous work—showing an association with factors like the flu and the use of certain medicines in pregnant women, for instance—provide more evidence that environmental factors affecting the womb, including what we eat and where we live, are meaningful in terms of autism risk.
“The exciting thing about looking at environment, or environment and genes in conjunction with each other, is this provides the possibility of intervention,” said Irva Hertz-Picciotto, an environmental epidemiologist at the University of California, Davis, who presented the study on insecticides.
Speaking in a packed auditorium at the International Society for Autism Research annual conference here, Marc Weisskopf of the Harvard School of Public Health presented results from a large national study, known as the Nurses’ Health Study II. The research suggested that a mother’s exposure to high levels of certain types of air pollutants, such as metals and diesel particles, increased the risk of autism by an average of 30% to 50%, compared with women who were exposed to the lowest levels.
Dr. Weisskopf and his colleagues examined levels of some particles and pollutants that the U.S. Environmental Protection Agency has measured and studied across the country in the locations where the approximately 330 women from the study who reported having a child with autism lived. They compared the levels with 22,000 women who didn’t have a child with autism, focusing on 14 pollutants that had been previously reported in the literature as possibly linked to autism.
The results mimicked those of previously published work on traffic pollution and autism risk in California. The consistency of findings across studies “certainly makes me start to feel much more certain that we’re on a path to finding something environmental that’s playing a role here,” said Dr. Weisskopf, a professor of environmental health and epidemiology. “At this stage it does seem there’s something related to air pollution.”
Data from another large study, known as the Charge study, also presented Friday, found for the first time that mothers who reported that they had taken iron supplements just before or early on in pregnancy had a 40% decrease in associated risk of having a child with autism, an effect similar in magnitude to that of folic-acid supplementation and its reduction of certain birth defects, said Rebecca Schmidt, a professor of public-health sciences UC Davis.
Her team compared the mothers of 510 kids with an autism-spectrum disorder to mothers of 341 kids without autism. Mothers completed a phone survey that included questions on many types of environmental exposures, including supplements like prenatal vitamins, multivitamins and nutrient-specific vitamins, cereal and protein bars, which are often fortified with iron and other nutrients. They weren’t asked about other dietary sources of iron, such as red meat and leafy green vegetables.
Dr. Schmidt cautioned that women shouldn’t boost iron intake without getting their levels checked by a doctor, because too much iron can lead to toxicity. “It’s much easier to change your diet or supplemental intake than it is to change your exposure to many other toxins,” said Dr. Schmidt.
In a separate analysis of the Charge data, UC Davis researchers also found a relationship between exposure to some insecticides in the household, such as bug foggers, and features of autism, but more research is needed to understand why there is a potential link, said Dr. Hertz-Picciotto.
Write to Shirley S. Wang at firstname.lastname@example.org
A version of this article appeared May 4, 2013, on page A3 in the U.S. edition of The Wall Street Journal, with the headline: Autism Linked to Environmental Factors.