Air pollution and risk of type 2 diabetes mellitus: A systematic review and meta-analysis

Aim: Whether exposure to relatively high levels of air pollution is associated with diabetes occurrence remains unclear. We sought to assess and quantify the association between exposure to major air pollutants and risk of type 2 diabetes. Methods: PubMed and EMBASE databases (through September 2013) were searched using a combination of terms related to exposure to gaseous (NO₂ and NO_x) or particulate matter pollutants (PM_2.5, PM₁₀ and PM_10-2.5) and type 2 diabetes. Descriptive and quantitative information were extracted from selected studies. We used random-effects models meta-analysis to derive overall risk estimates per type of pollutant. Results: We included ten studies (five cross-sectional and five prospective), assessing the effects of air pollutants on the occurrence of diabetes. In prospective investigations, the overall effect on diabetes occurrence was significant for both NO₂ (adjusted hazard ratio [HR], 1.13; 95% confidence interval [95%CI], 1.01-1.22; p<0.001; I²=36.4%, p_{heterogeneity}=0.208) and PM_2.5 (HR, 1.11; 95%CI, 1.03-1.20; p<0.001; I²=0.0%, p_{heterogeneity}=0.827). Odds ratios were reported by two cross-sectional studies which revealed similar associations between both NO₂ and PM_2.5 with type 2 diabetes. Across studies, risk estimates were generally adjusted for age, gender, body mass index and cigarette smoking. Conclusions: Available evidence supports a prospective association of main air pollutants with an increased risk for type 2 diabetes. This finding may have implications for population-based strategies to reduce diabetes risk.