Air Pollution May Raise Autism Risk
Nov. 26, 2012 -- Being exposed to high levels of air pollution from traffic may raise the risk of autism, researchers say.
"Children exposed to higher levels of traffic-related pollutants during pregnancy or during the first year of life were at increased risk of autism compared to children exposed to the lowest level," says Heather E. Volk, PhD, MPH, assistant professor of research at the University of Southern California Keck School of Medicine.
The risk differed depending on timing.
During pregnancy, the highest exposures to pollution were linked with a two-times-higher risk of autism, she says. High levels during the child's first year tripled the risk.
The study is published online in the Archives of General Psychiatry.
Air Pollution & Autism Risk
Autism is a diverse disorder marked by problems in communicating and interacting socially. It now affects about 1 in 88 children in the U.S.
Researchers have been looking at the potential role of air pollution in autism only for about three years, Volk says.
Air pollution has been linked with a variety of ill health outcomes, she says, including babies being born small for their gestational age. "When you think about the birth outcome literature, looking at air pollution [and autism risk] makes some sense," she says.
In 2011, Volk's team reported a higher risk of autism for children whose families lived within about 1,000 feet of a freeway.
For the new study, she looked at data from 279 children with autism and a comparison group of 245 children without it.
At the time they started, the children were ages 2 to 5 years.
Volk used the mothers' addresses to estimate exposure to pollution during each trimester of pregnancy and during the child's first year of life.
They used information from the EPA and did traffic modeling to figure out how much traffic-related air pollution was at each location. They also looked at exposure to particulate matter and nitrogen dioxide.
In her previous study, Volk says, she just looked at how far people lived from roads. The new study went further.
"Now we consider how busy the road was, traffic density, volume of traffic, and how often the road is traveled," she says.
The risk of autism was higher for those exposed to more pollution, either before birth or during their first year.
Based on the findings, however, Volk says she can't say that living in a specific area is worse than another.
For instance, those who live in a rural area might be close to a very busy high-traffic intersection, increasing pollution exposure.
She found a link or association. It does not prove cause and effect.
The link held after she considered other factors that affect risk, such as prenatal smoking, the mother's age, race, and ethnicity.