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Association Between Long-Term Exposure to Fine Particulate Matter and Obesity in Children: A National Representative Cross-Sectional Study in China

Background: Childhood obesity is a global health issue; and limited evidence suggests that air pollution may be a contributing factor. This study aims to examine whether long-term exposure to fine particulate matter (PM2·5) is associated with obesity status in a nationally representative sample of schoolchildren in China. 
 
Methods: The study population consisted of 41,439 schoolchildren of 6–17 years old and recruited from 30 Chinese provinces using a multi-stage stratified sampling method. Children were measured for their weight and height and for their demographic information via a questionnaire survey. Individual-level exposure to daily PM2·5 in the year prior to the survey were estimated using a combination of ground level monitoring data, satellite data, and chemical transport models. Obseity status was classified following the Chinese national standards. The association between obesity status and long-term PM2·5 exposure was examined using weighted logistic regressions adjusted for potential confounders. 
 
Findings: In this national representive sample of school-age children, the prevalence of normal weight, overweight, and obesity were 78·5%, 12·4%, and 9·0%, respectively. Annual averages of PM2·5 were 62·1±21·3 μg/m3 with a range of 26·3-130·6 μg/m3. The risk of obesity increased by 9·0% (95% CI: 3·0–15·0%) per 10 μg/m3 increase in PM2·5 annual exposure. The PM2·5-associated risk was significantly elevated in older age groups, children living in urban areas, and those from lower socioeconimc families (interaction p-values<0·05). The associations remained robust when long-term PM2·5 exposure was estimated using an averaging time longer than one year (up to five years). 
 
Interpretation: Approximately one in five Chinese schoolchildren was overweight or obese. Long-term exposure to PM2·5 was significantly and positively associated with obesity status. This finding suggests that PM2·5 exposure reduction may alleviate the epidemic of childhood obesity. 
 
Funding Statement: National Science Foundation (41977374) and the National Key Research and Development Program of China (2016YFC1302501). 
 
Declaration of Interests: We declare no competing interests. 
 
Ethics Approval Statement: The survey protocols were reviewed and approved by the ethical board of the National Institute for Nutrition and Food Safety, Chinese Centers for Disease Control and Prevention before the study commenced in 2013 (Reference No.: 2013–018).