Impact of ambient air pollution on obesity: a systematic review

Background/objectives Over 80% of the global populations living in urban areas are exposed to air quality levels that exceed the World Health Organization limits. Air pollution may lead to unhealthy body weight through metabolic dysfunction, chronic disease onset, and disruption of regular physical activity. Subjects/methods A literature search was conducted in the PubMed and Web of Science for peer-reviewed articles published until September 2017 that assessed the relationship between air pollution and body weight status. A standardized data extraction form was used to collect methodological and outcome variables from each eligible study. Results Sixteen studies met the selection criteria and were included in the review. They were conducted in seven countries, including the US (n = 9), China (n = 2), Canada (n = 1), Italy (n = 1), The Netherlands (n = 1), Serbia (n = 1), and South Korea (n = 1). Half of them adopted a longitudinal study design, and the rest adopted a cross-sectional study design. Commonly examined air pollutants included PM, NO2, SO2, O-3, and overall air quality index. Among a total of 66 reported associations between air pollution and body weight status, 29 (44%) found air pollution to be positively associated with body weight, 29 (44%) reported a null finding, and the remaining eight (12%) found air pollution to be negatively associated with body weight. The reported associations between air pollution and body weight status varied by sex, age group, and type of air pollutant. Three pathways hypothesized in the selected studies were through increased oxidative stress and adipose tissue inflammation, elevated risk for chronic comorbidities, and insufficient physical activity. Conclusions Concurrent evidence regarding the impact of air pollution on body weight status remains mixed. Future studies should assess the impact of severe air pollution on obesity in developing countries, focus on a homogenous population subgroup, and elucidate the biomedical and psychosocial pathways linking air pollution to body weight.