The study, published Monday in the Archives of General Psychiatry, compared 279 autistic children with 245 children who didn't have the social and communications disorder. Researchers said the children who lived in homes with the highest estimated levels of air pollution from traffic were three times more likely to be autistic than those with the lowest predicted exposure.
The cause of autism is unknown, though genetic factors are probably important, according to the National Institutes of Health. Among other environmental causes that have been suspected are diet, digestive tract changes, mercury poisoning and vaccine sensitivity.
"The public health implications of these findings are large because air pollution exposure is common and may have lasting neurological effects," the authors, led by Heather Volk, an assistant professor of preventive medicine at the University of Southern California in Los Angeles, wrote in their study.
The increased risk from air pollution generated by car and truck traffic may be caused by exhaust particles, though the study didn't measure the particulate matter at any of the homes of the children analyzed. Instead, researchers modeled what they expected the air pollution was, based on the mother's address. Additionally, the research didn't explore sources of indoor pollution, such as second-hand smoke.
The Centers for Disease Control and Prevention reported in March that 1 in 88 children in the U.S. had autism or a related disorder in 2008, the latest period for which data is available. That was a 23 percent rise from 2006, the agency's researchers reported, saying it was unclear how much of the increase was attributed to greater awareness of the disease.
Pollution from small particles is known to cause heart attacks, early death, decreased lung function and asthma, according to the U.S. Environmental Protection Agency. The particles, which come from coal plants, car exhaust, fireplaces, furnaces and other sources, are common in urban areas.
Decreasing pollution by about 7 micrograms per cubic meter may lead to a five-month increase in life expectancy, previous research suggested. More study is needed to know how air pollution interacts with autism, the study authors said.
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