Polluted Air Linked to Autism Risk

Pregnant women who live with smog at higher risk, but experts caution the finding is not definitive

By Denise Mann

HealthDay Reporter

TUESDAY, June 18 (HealthDay News) -- Pregnant women who live in smog-filled areas may be twice as likely to have children with autism, a new study suggests.

"The study does not prove that pollution increases risk for autism. It found an association," cautioned lead author Andrea Roberts, a research associate at the Harvard School of Public Health in Boston. "It adds to the weight of the evidence that there may be something in air pollution that increases risk for autism."

Researchers compared exposure to air pollution among 325 women who had a child with autism and 22,000 women who did not. The women were participants in the Nurses' Health Study II. Pollutants measured included diesel particulate matter, lead, manganese, mercury, methylene chloride, and a combined measure of metal exposure.

Twenty percent to 60 percent of the women lived in areas considered highly polluted. And the study showed that: those women who lived in the 20 percent of locations that had the highest levels of diesel particulates or mercury in the air were twice as likely to have a child with autism, compared to those who lived in the 20 percent of areas with the lowest levels of these pollutants.

In addition, those who lived in the 20 percent of locations with the highest levels of lead, manganese, methylene chloride, and combined metal exposure were about 50 percent more likely to have a child with autism than those who lived in the 20 percent of areas with the lowest concentrations.

The findings held even after the researchers took into account other factors known to affect autism risk, such as income, education and smoking during pregnancy. Overall, the association was stronger for boys than it was for girls, but the number of girls included in the new study was too low to draw any firm conclusions.

The findings, which were published June 18 online in Environmental Health Perspectives, do add to a growing body of research that suggests the air women breathe while pregnant is one of many factors linked to autism risk. Previous studies have shown that pregnant women who live in polluted areas or close to freeways are more likely to have a child with autism, but the studies were done regionally. The new data is nationwide.

Exactly how, or even if, air pollution affects the developing brain is murky. "By definition, pollution is stuff that is not good for us," Roberts said.

Still, the overall increase in autism risk that may be attributed to pollution is low. "Let's say a woman's risk for having a child with autism is one in 100, women who live in the most polluted cities have a risk that is about one in 50, which means that 49 children would not have autism," Roberts said.

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