Childhood autism spectrum disorders and exposure to nitrogen dioxide, and particulate matter air pollution: A review and meta-analysis.
OBJECTIVE
Genetic and environmental factors have been recognized to play an important role in autism. The possibility that exposure to outdoor air pollution increases the risk of autism spectrum disorder (ASD) has been an emerging area of research. Herein, we present a systematic review, and meta-analysis of published epidemiological studies that have investigated these associations.


METHODS
We undertook a comprehensive search strategy to identify studies that investigated outdoor air pollution and autism in children. Overall, seven cohorts and five case-control studies met our inclusion criteria for the meta-analysis. We summarized the associations between exposure to air pollution and ASD based on the following critical exposure windows: (i) first, second and third trimester of pregnancy, (ii) entire pregnancy, and (iii) postnatal period. Random effects meta-analysis modeling was undertaken to derive pooled risk estimates for these exposures across the studies.


RESULTS
The meta-estimates for the change in ASD associated with a 10μg/m3increase in exposure in PM2.5and 10 ppb increase in NO2during pregnancy were 1.34 (95% CI:0.83, 2.17) and 1.05 (95% CI:0.99, 1.11), respectively. Stronger associations were observed for exposures received after birth, but these estimates were unstable as they were based on only two studies. O3exposure was weakly associated with ASD during the third trimester of pregnancy and during the entire pregnancy, however, these estimates were also based on only two studies.


CONCLUSIONS
Our meta-analysis support the hypothesis that exposure to ambient air pollution is associated with an increased risk of autism. Our findings should be interpreted cautiously due to relatively small number of studies, and several studies were unable to control for other key risk factors.
Department of Health Sciences, Carleton University, Ottawa, Ontario, Canada; Epistream Consulting Inc, Ottawa, Ontario, Canada.
Marie-Claire
MC
Flores-Pajot
Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Marianna
M
Ofner
Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Minh T
MT
Do
Air Health Science Division, Health Canada, Ottawa, Ontario, Canada; School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, Ontario, Canada.
Eric
E
Lavigne
Department of Health Sciences, Carleton University, Ottawa, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; Epistream Consulting Inc, Ottawa, Ontario, Canada. Electronic address: Paul.Villeneuve@carleton.ca.
Paul J
PJ
Villeneuve
D000397:Air Pollution / Q000009:adverse effects / Q000032:analysis*; D001321:Autistic Disorder / Q000139:chemically induced / Q000453:epidemiology*; D002648:Child; D016208:Databases, Factual; D005260:Female; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects / Q000032:analysis*; D009585:Nitrogen Dioxide / Q000009:adverse effects / Q000032:analysis*; D052638:Particulate Matter / Q000009:adverse effects / Q000032:analysis*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology; D012621:Seasons
D052638:Particulate Matter; D009585:Nitrogen Dioxide
Air pollution; Autism spectrum disorder; Fine particulate matter; Meta-analysis; Review