Exposure to ambient ultrafine particles and nitrogen dioxide and incident hypertension and diabetes

Background — Previous studies reported that long-term exposure to traffic-related air pollution may increase the incidence of hypertension and diabetes. However, little is known about the associations of ultrafine particles (≤0.1 micrometers in diameter) with these two conditions.

Methods — We conducted a population-based cohort study to investigate the associations between exposures to ultrafine particles and nitrogen dioxide (NO2) and the incidence of diabetes and hypertension. Our study population included all Canadian-born residents aged 30 to 100 years who lived in the City of Toronto, Canada from 1996 to 2012. Outcomes were ascertained using validated province-wide databases. We estimated annual concentrations of ultrafine particles and NO2 using land-use regression models and assigned these estimates to participants' annual postal-code addresses during the follow-up period. Using random-effects Cox proportional hazards models, we calculated hazard ratios (HRs) and 95% confidence intervals (CIs) for ultrafine particles and NO2, adjusted for individual- and neighborhood-level covariates. We considered both single- and multi-pollutant models.

Results — Each interquartile change in exposure to ultrafine particles was associated with increased risk of incident hypertension (HR=1.03; 95%CI: 1.02-1.04) and diabetes (HR=1.06; 95%CI: 1.05-1.08) after adjusting for all covariates. These results remained unaltered with further control for fine particulate matter (≤2.5 micrometers; PM2.5) and NO2. Similarly, NO2 was positively associated with incident diabetes (HR=1.06; 95%CI: 1.05-1.07) after controlling for ultrafine particles and PM2.5.

Conclusion — Exposure to traffic-related air pollution including ultrafine particles and NO2 may increase the risk for incident hypertension and diabetes.