Long-term exposure to fine particulate matter air pollution and type 2 diabetes mellitus in elderly: A cohort study in Hong Kong

Background: Evidence for the link between long-term air pollution exposure and occurrence of diabetes is limited and the results are mixed. Objectives: We aimed to assess the association of long-term residential exposure to fine particulate matter (PM2.5) with the prevalence and incidence of type 2 diabetes mellitus (DM). Methods: This is a prospective cohort study. We studied 61,447 participants of the Chinese Elderly Health Services cohort in Hong Kong enrolled 1998-2001 and followed participants without DM at baseline to 31 December 2010 to ascertain the first hospital admissions for type 2 DM. Yearly mean residential PM2.5 exposure was predicted based on satellite data. Logistic regression and time-varying Cox regression model were used to evaluate the prevalence and incidence risk of DM associated with PM2.5 while adjusting for potential individual and neighborhood confounders. Results: There were 61,447 participants included in the study of prevalent DM, and in 53,905 participants without DM at baseline we studied incident type 2 DM. Over a mean follow-up of 9.8 years, we ascertained 806 incident cases of type 2 DM. After adjusting for potential confounders, the odds ratio (OR) for every interquartile range (3.2 mu g/m(3)) increase of PM2.5 concentration was 1.06 (95% confidence interval (CI): 1.01-1.11) for prevalent DM, while the corresponding hazard ratio (HR) was 1.15 (95% CI: 1.05-1.25) for incident type 2 DM. Conclusions: Long-term exposure to high levels of PM2.5 may increase the risk of both prevalence and incidence of type 2 diabetes mellitus in Hong Kong elderly population.