Association between ambient air pollution and diabetes mellitus in Europe and north America : systematic review and meta-analysis

BACKGROUND: Air pollution is hypothesized to be a risk factor for diabetes. Epidemiological evidence is inconsistent and has not been systematically evaluated.OBJECTIVES: We systematically reviewed epidemiological evidence on the association between air pollution and diabetes, and synthesized results of studies on type 2 diabetes (T2DM).METHODS: We systematically searched electronic literature databases (last search 29 April 2014) for studies reporting the association between air pollution (particle concentration or traffic exposure) and diabetes (type 1, type 2 or gestational). We systematically evaluated risk of bias and role of potential confounders in all studies. We synthesized reported associations with T2DM in meta-analyses using random effect models and conducted various sensitivity analyses.RESULTS: We included 13 studies (eight on T2DM, two on type 1, three on gestational diabetes), all conducted in Europe or North-America. Five studies were longitudinal, five cross-sectional, two case-control and one ecologic. Risk of bias, air pollution assessment, and confounder control varied across studies. Dose-response effects were not reported. Meta-analyses of three studies on PM2.5 (particulate matter >2.5 µm in diameter) and four studies on NO2 (nitrogen dioxide) showed increased risk of T2DM by 8-10% per 10 µg/m3 increase in exposure [PM2.5: 1.10 (95% CI: 1.02, 1.18); NO2: 1.08 (95% CI: 1.00, 1.17)]. Associations were stronger in females. Sensitivity analyses showed similar results.CONCLUSION: Existing evidence indicates a positive association of air pollution and T2DM risk albeit there is high risk of bias. High quality studies assessing dose-response effects are needed. Research should be expanded to developing countries where outdoor and indoor air pollution are high.