MONDAY, Nov. 26, 2012 (HealthDay News) -- Children exposed to air pollution from traffic and other sources while in the womb and during their first year may be at an increased risk for autism, a new study suggests.
Infants exposed to the highest levels of air pollution were three times more likely to develop autism than those exposed to the lowest levels, researchers found.
"There is evidence that the immune system might be associated with autism, and pollution affects these same pathways," said lead researcher Heather Volk, assistant professor of preventive medicine at the University of Southern California, in Los Angeles.
It is also possible that the toxic chemicals in pollution are related to the increased risk of autism, she said, and these pollutants may trigger a genetic predisposition to the condition.
"We are not saying that air pollution causes autism," Volk said. "But it does appear that this may be one potential risk for autism. We are beginning to understand that pollution affects the developing fetus."
The report was published in the Nov. 26 online edition of the Archives of General Psychiatry.
For the study, Volk's team looked at the connection of autism with exposure to air pollution among 279 children with autism. They compared these children to 245 children without the condition. All the children took part in a California study on autism risks, genetics and the environment.
To estimate the amount of pollution the children were exposed to, the researchers used the mothers' address. Pollution from traffic was estimated using U.S. Environmental Protection Agency data on air quality.
Children exposed to the highest levels of traffic air pollution during pregnancy were nearly twice as likely to develop autism as children exposed to the least air pollution, the researchers found. And between birth and 1 year of age, children exposed to the most traffic-related pollution were 3.1 times more likely to develop autism.
The risk seemed to be linked to what is called particulate matter pollution and nitrogen dioxide -- commonly known as smog -- the researchers noted.
Autism is a neurodevelopmental condition that appears to be caused by both genetic and environmental factors. Autism spectrum disorder is an umbrella term that includes a range of symptom severity. Common factors include problems with communication, social interaction and repetitive behaviors. An estimated one in 88 U.S. children has some form of autism.
Geraldine Dawson, chief science officer of Autism Speaks and a professor of psychiatry at the University of North Carolina at Chapel Hill, wrote an accompanying journal editorial.
"Over the past decade, there has been an explosion of research on autism, which has paralleled the dramatic increase in autism prevalence," Dawson said. "However, we still lack effective treatments and more research funding is needed to address the public health crisis that autism has become."
New research methods are helping to explain the biology of autism and its causes, according to Dawson, who said the latest study "confirms earlier studies that exposure to environmental toxins, especially during the prenatal period, can increase the risk of autism."
Environmental toxins may be one factor contributing to abnormalities in immune functioning that have been associated with autism, she added.
Dawson noted that another study in the same journal issue found more evidence of abnormal immune function in people with autism.
"We don't know whether these immune abnormalities are a cause or a response to having autism. Either way, these findings are an important clue that the immune system plays a role in autism," she said. "There is an urgent need for more research on environmental factors that can influence prenatal brain development and potentially increase risk for autism."
Although the California study found an association between air pollution exposure and autism risk in children, it did not prove a cause-and-effect relationship.
To learn more about autism, visit the U.S. Centers for Disease Control and Prevention.