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Originally published Tuesday, November 27, 2012 at 6:20 PM

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Autism, early exposure to traffic pollution linked

A new study reports children who were exposed to the highest levels of traffic-related air pollution during gestation and in early infancy were three times more likely to be diagnosed with autism than those whose exposure was very low.

Los Angeles Times

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LOS ANGELES — In a finding that points to a link between environmental toxins and autism, a new study shows that children who were exposed to the highest levels of traffic-related air pollution during gestation and in early infancy were three times more likely to be diagnosed with the neurodevelopmental disorder than were those who had very low exposure.

The study, published Monday in the Archives of General Psychiatry, found early exposure to high levels of air pollution in general was linked to a higher likelihood of autism in a group of more than 500 children followed for several years from birth.

The researchers gathered regional air-quality data and used detailed calculations to estimate the air quality around the residence in which the mother spent her pregnancy and the child spent infancy.

Their findings suggest the link between air pollution and autism is evident largely at the highest levels of exposure, and slightly higher when the exposure comes later in a woman's pregnancy.

The strongest link was found between exposure to nitrogen dioxide — a pollutant found plentifully around freeways — and autism, while exposure to particulates was less strongly linked to autism.

The researchers found the link between traffic-related air pollutants held steady after they took into account parental education, ethnicity, smoking during pregnancy, or how densely populated the region was. That suggests the finding is not just a backhanded way of capturing some link between autism and the socioeconomic or demographic factors in which a child is raised.

The study refines earlier findings by the same authors that linked autism to a child's living near a freeway.

While the authors caution that this link is not proof air pollution causes autism, they do suggest there are several ways in which air pollutants could influence the development of a child's brain in ways that could result in the sorts of neurodevelopmental problems seen in autism.

Diesel exhaust particles and polycyclic aromatic hydrocarbons, which are present in traffic pollutants, have been shown to interfere with gene expression important in healthy brain development.

Other research suggests traffic-related air pollutants induce inflammatory reactions in the brain and throughout the body.

The article was one of three studies published in the Archives of General Psychiatry probing autism's possible origins and its effects on the brain. Those come at a time when the diagnosis of autism spectrum disorder in U.S. children has skyrocketed. In the last six years alone, it has increased 78 percent.

Collectively, the studies "point to an urgent need for more research on prenatal and early postnatal brain development in autism, with a focus on how genes and early development combine to increase risk" for autism, wrote Geraldine Dawson, chief science officer of Autism Speaks.

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