Long-term exposure to particulate air pollution and incidence of Parkinson's disease: A nationwide population-based cohort study in South Korea

There has been increasing interest in the neurological impact of particulate matter (PM). However, its association with the incidence of Parkinson's disease (PD) remains unclear. We selected 313,355 participants satisfying inclusion criteria from the National Health Insurance Service-National Sample Cohort based on the nationwide population of South Korea, and followed them up from January 2007 through December 2015. Individual-level long-term PM exposure was assessed as the five time-varying average concentrations estimated for the previous 1, 2, 3, 4 and 5 years on each year (until censored or event occurred) at the district-level residential addresses of participants using a previously validated prediction model. Incident PD was defined as the first diagnosis accompanied by anti-PD medication prescription from 2007 through 2015. Time-varying Cox proportional hazards models were employed to estimate the hazard ratio (HR) of incident PD for long-term PM exposure, adjusting for individual-and area-level covariates. During the 8 years (2,745,389 person-years) of follow-up for a total of 313,355 participants (mean [range] age, 48.9 [19-87] years; 169,571 males [54.1%]), 2621 participants (0.8%) developed PD. The HR of incident PD per interquartile range (3.3 mu g/m(3)) increase in fine PM (PM2.5) for the previous 1 year was 1.08 (95% confidence interval: 1.01-1.19). In subgroup-specific analyses, HRs for PM2.5 were significant among older participants, males, participants living in metropolitan cities, ibuprofen users, and participants with comorbidities (HR: 1.10-1.20). Long-term exposure to PM2.5 might play a role in PD development.