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Air pollution increased children’s risk for autism
Exposure to regional pollution and pollution from local traffic sources during pregnancy and the first year of life has been associated with more than a twofold risk for autism in children, according to recent study results.
“This work has broad potential public health implications,” study researcher Heather Volk, PhD, assistant professor of preventive medicine at the Keck School of Medicine at the University of Southern California, said in a press release. “We’ve known for a long time that air pollution is bad for our lungs, and especially for children. We’re now beginning to understand how air pollution may affect the brain.”
Volk and colleagues conducted a population-based case-control study that included 279 children with autism and 245 children with typical development. The children were part of the Childhood Autism Risks from Genetics and the Environment study.
The researchers used mothers’ addresses from birth certificates and addresses reported from a residential history to estimate exposure to air pollutants for each trimester of pregnancy and during the child’s first year of life. Pollution from local traffic sources was determined using a dispersion model. Air pollution levels were derived from the Environmental Protection Agency’s Air Quality System to determine exposure to nitrogen dioxide (NO2) and fine particulate matter less than 2.5 mcm (PM2.5) and 10 mcm (PM10) in diameter.
“We took into account how far away people lived from roads, meteorology such as which way the wind was blowing, how busy the road was, and other factors to study traffic-related pollution,” Volk said. “We also examined data from air quality monitors, which measure pollution over a larger region that could come from traffic, industry, rail yards, or many other sources.”
Results show that children with autism were more likely to live in areas with the greatest exposure to traffic-related sources of air pollution during gestation (adjusted OR=1.98; 95% CI, 1.20-3.31) and during the child’s first year of life (AOR=3.10; 95% CI, 1.76-5.57) vs. children with typical development. Autism was also associated with regional exposure to NO2, PM2.5 and PM10 during gestation (exposure to NO2: AOR=1.81; 95% CI, 1.37-3.09; exposure to PM2.5: AOR=2.08; 95% CI, 1.93-2.25; and exposure to PM10: AOR=2.17; 95% CI, 1.49-3.16) and during the child’s first year of life (exposure to NO2: AOR=2.06; 95% CI, 1.37-3.09; exposure to PM2.5: AOR=2.12; 95% CI, 1.45-3.10; and exposure to PM10: AOR=2.14; 95% CI, 1.46-3.12).
“Research on the effects of exposure to pollutants and their interaction with susceptibility factors may lead to the identification of the biologic pathways that are activated in autism and to improved prevention and therapeutic strategies,” the researchers wrote. “Although additional research to replicate these findings is needed, the public health implications of these findings are large because air pollution exposure is common and may have lasting neurological effects.”
Disclosure: See the study for a full list of financial disclosures.
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The study by Volk et al examines the role of air pollution’s impact on autism in a time of increased prevalence of the disorder. Explanations for this increased rate of autism have generally focused on increased awareness of the condition and improved diagnostics, yet evidence builds indicating a role of the environment as a risk factor. Similar with concerns raised about global warming, the issues are large and difficult to measure.
This case-control study features solid diagnostic design and uses complicated models of air quality dispersion combined with EPA air quality data to calculate odds ratios for developing autism. Overall, children living in the highest 25% level of traffic-related air pollution have about three times increased risk of developing autism. Exposure to particulate matter and nitrous dioxide was associated with twice the risk. Effects were noted with exposure throughout pregnancy, but the effect was greatest for exposure during the first year of life.
By discussing possible biologic pathways, the study offers some tantalizing clues to the etiology of autism in general. Autism is felt to be polygenic in origin in that multiple genes and diverse pathways are linked with the disorder (Berg JM. Genome Biol. 2012;13:247), but not all cases of autism have a clear genetic link. Environmental factors such as toxin exposure may impact ‘fetal programming’ through their effect on epigenetic expression, autoimmune factors and disruption of cellular functions (Szatmari P. Arch Gen Psychiatry. 2011;68:1091-1092). The study by Volk et al suggests efforts to reduce exposure to air pollution could play a role in prevention of this developmental disorder.