Several new studies presented at the International Society for Autism Research annual conference back up the notion that environmental factors before birth may play an important role in the development of autism.
The causes of autism aren’t well understood but are thought to be multifaceted. Genetics likely account for anywhere from 35 percent to 60 percent of the risk, say many researchers.
But some experts and parents believe that nutrition and other environmental factors may play a role as well.
In one study, pregnant women who were exposed to certain levels of air pollution were more likely to have a child with autism. Another study suggested that iron supplements before and early in pregnancy may lower the risk, and a third suggested a link between a higher risk and the use of various household insecticides.
The new research shows only associations and doesn’t prove causality, and each factor itself likely accounts for only a small portion of the risk for autism, say researchers. But the findings, combined with previous research, provide more evidence that environmental influences in the womb 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, Ph.D., an environmental epidemiologist at the University of California, Davis, who presented the study on insecticides.
Marc Weisskopf, Ph.D., of the Harvard School of Public Health presented the results from the Nurses’ Health Study II. This 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 percent to 50 percent, compared with women who were exposed to the lowest levels.
Weisskopf and his team examined levels of certain particles and pollutants that the U.S. Environmental Protection Agency has measured and studied, in the locations where approximately 330 moms of children 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 as possibly linked to autism.
The results mimicked those of previously published work on traffic pollution 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 Weisskopf, a professor of environmental health and epidemiology.
“At this stage it does seem there’s something related to air pollution.”
In another large study, known as the Charge study, mothers who reported that they had taken iron supplements just before or early on in pregnancy had a 40 percent decrease in associated risk of having a child with autism.
This is similar in magnitude to folic acid supplementation and its associated reduction of certain birth defects, said Rebecca Schmidt, Ph.D., a professor of public-health sciences at UC Davis.
The study included the mothers of 510 kids with an autism spectrum disorder (ASD) as well as 341 controls.
Mothers completed a telephone 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. The participants weren’t asked about other dietary sources of iron, such as red meat and leafy green vegetables.
“It’s much easier to change your diet or supplemental intake than it is to change your exposure to many other toxins,” added Schmidt.
Schmidt cautioned, however, that women shouldn’t increase their iron intake without having their levels checked first, since too much iron can lead to toxicity.