Smog and air pollution linked to an increased autism risk

Could smog and polluted air be one of the triggers for autism spectrum disorders?

Women exposed to high levels of fine particulate matter specifically during pregnancy — particularly during the third trimester — may face up to twice the risk of having a child with autism than mothers living in areas with low particulate matter.

smog - car exhaust - particulate matter

The greater the exposure, the greater the risk, researchers found. It was the first US-wide study exploring the link between airborne particulate matter and autism.
The third trimester most crucial

“Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders,” said Marc Weisskopf, associate professor of environmental and occupational epidemiology and senior author of the study reported by the Harvard School of Public Health (HSPH).

“The specificity of our findings for the pregnancy period, and third trimester in particular, rules out many other possible explanations for these findings.”

woman in third trimester of pregnancyPrior studies have suggested that, in addition to genetics, exposure to airborne environmental contaminants — particularly during pregnancy and early life — may affect risk of autism. This study focused specifically on the pregnancy period.

Air quality – or lack thereof

The study population included offspring of participants living in all 50 states in Nurses’ Health Study II, a cohort of more than 116,000 female US nurses begun in 1989. The researchers collected data on where participants lived during their pregnancies as well as data from the US Environmental Protection Agency and other sources on levels of fine particulate matter air pollution (PM2.5) — particles 2.5 microns in diameter or smaller — in locations across America

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According to the Journal of the American Medical Association (JAMA), in 1997, the standard for airborne particulate matter was revised, maintaining the previous indicator of particulate matter of less than or equal to 10 µm in aerodynamic diameter (PM10) and creating a new indicator for fine particulate matter of less than or equal to 2.5 µm in aerodynamic diameter (PM2.5).

The EPA notes that “fine particles,” such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air. Particles in this size range have a much greater probability of reaching the small airways and the alveoli (air sacs) of the lung than do larger particles, the JAMA adds.

Kids with and without autism

The researchers identified 245 children who were diagnosed with autism spectrum disorder (ASD) and a control group of 1,522 children without ASD during the time period studied.



The researchers explored the association between autism and exposure to PM2.5 before, during, and after pregnancy. They also calculated exposure to PM2.5 during each pregnancy trimester.

Exposure to PM2.5 was significantly associated with autism during pregnancy, but not before or after, the study found. And during the pregnancy, the third trimester specifically was significantly associated with an increased risk.

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Little association, however, was found between air pollution from larger-sized particles (PM10-2.5) and autism.

“The evidence base for a role for maternal exposure to air pollution increasing the risk of autism spectrum disorders is becoming quite strong,” said Weisskopf. “This not only gives us important insight as we continue to pursue the origins of autism spectrum disorders, but as a modifiable exposure, opens the door to thinking about possible preventative measures.”



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