Risk of incident diabetes in relation to long-term exposure to fine particulate matter in Ontario, Canada

Background — Laboratory studies suggest that fine particulate matter (2.5µm in diameter or less; PM_2.5) can activate pathophysiological responses which may induce insulin resistance and type-2 diabetes. However, epidemiological evidence relating PM_2.5 and diabetes is sparse, particularly for incident diabetes.

Objectives — The researchers conducted a population-based cohort study to determine whether long-term exposure to ambient PM_2.5 is associated with incident diabetes.

Methods — The researchers assembled a cohort of 62,012 nondiabetic adults who lived in Ontario, Canada and completed one of five population-based health surveys between 1996 and 2005. Follow-up extended until December 31, 2010. Incident diabetes diagnosed between 1996 and 2010 was ascertained using the Ontario Diabetes Database, a validated registry of persons diagnosed with diabetes (sensitivity=86%, specificity=97%). Six-year average concentrations of PM_2.5 at the postal codes of baseline residences were derived from satellite observations. The researchers used Cox proportional hazards models to estimate the associations, adjusting for various individual-level risk factors and contextual covariates such as smoking, body mass index, physical activity, and neighbourhood-level household income. The researchers also conducted multiple sensitivity analyses. In addition, the researchers examined effect modification for selected comorbidities and sociodemographic characteristics.

Results — There were 6,310 incident cases of diabetes over 484,644 total person-years of follow up. The adjusted hazard ratio for a 10-µg/m³ increase in PM_2.5 was 1.11 (95% CI: 1.02, 1.21). Estimated associations were comparable among all sensitivity analyses. The researchers did not find strong evidence of effect modification by comorbidities or sociodemographic covariates.

Conclusions — This study suggests that long-term exposure to PM_2.5 may contribute to the development of diabetes.