Particulate matter pollutants and risk of type 2 diabetes: a time for concern?

World Health Organization estimates that worldwide in 2012 around 7 million deaths occurred prematurely due to air pollution, which is now the world's largest single environmental health risk. The higher premature mortality associated with air pollution is due to exposure to small particulate matter of 10 microns (PM10) or less in diameter. Exposure to air pollution has also been suggested as a contributing to diabetes incidence and progression. There are a number of possible biological pathways linking air pollutants to diabetes, including endothelial dysfunction, dysregulation of the visceral adipose tissue through inflammation, hepatic insulin resistance, elevated hemoglobin A1c level, elevated blood pressure, and alterations in autonomic tone, which may increase insulin resistance. The risk of future diabetes associated with exposure to 10 mu g/m(3) increase of PM2.5 has been quantified in the range of 10 to 27 %; the risk of diabetes mortality associated with PM2.5 appears to be quite lower, around 1 % for each increment exposure of 10 mu g/m(3) of both PM2.5 and PM10. Limitations of the current epidemiological evidence include the complex mixture of pollutants, the different design of the studies, the limited data available for non Western populations, and the lack of demonstration that improvement of air quality is associated with a decrease incidence of type 2 diabetes. Although the most sources of outdoor air pollution are well beyond the control of individuals, people should be informed that there are means to reduce the burden of air pollutants on diabetes risk, including avoidance of passive smoking, adoption of an healthy diet, and increasing leisure-time physical activity.