Air Pollution as a Risk Factor for Incident Chronic Obstructive Pulmonary Disease and Asthma. A 15-Year Population-Based Cohort Study

Abstract Rationale Current evidence on the relationship between long-term exposure to air pollution and new onset of chronic lung disease is inconclusive. Objectives To examine associations of incident chronic obstructive pulmonary disease (COPD) and adult-onset asthma with past exposure to fine particulate matter ≤ 2.5 μm in diameter (PM2.5), nitrogen dioxide (NO2), ozone (O3), and the redox-weighted average of NO2 and O3 (Ox) and characterize the concentration–response relationship. Methods We conducted a population-based cohort study of all Ontarians, aged 35–85 years, from 2001 to 2015. A 3-year moving average of residential exposures to selected pollutants with a 1-year lag were estimated during follow-up. We used Cox proportional hazard models and Aalen additive-hazard models to quantify the pollution–disease associations and characterized the shape of these relationships using newly developed nonlinear risk models. Measurements and Main Results Among 5.1 million adults, we identified 340,733 and 218,005 incident cases of COPD and asthma, respectively. We found positive associations of COPD with PM2.5 per interquartile-range (IQR) increase of 3.4 μg/m3 (hazard ratio, 1.07; 95% confidence interval, 1.06–1.08), NO2 per IQR increase of 13.9 ppb (1.04; 1.02–1.05), O3 per IQR increase of 6.3 ppb (1.04; 1.03–1.04), and Ox per IQR increase of 4.4 ppb (1.03; 1.03–1.03). By contrast, we did not find strong evidence linking these pollutants to adult-onset asthma. In addition, we quantified that each IQR increase in pollution exposure yielded 3.0 (2.4–3.6), 3.2 (2.0–4.3), 1.9 (1.3–2.5), and 2.3 (1.7–2.9) excess cases of COPD per 100,000 adults for PM2.5, NO2, O3, and Ox, respectively. Furthermore, most pollutant–COPD relationships exhibited supralinear shapes. Conclusions Air pollution was associated with a higher incidence of COPD but was not associated with a higher incidence of adult-onset asthma.