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

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 mu m in diameter (PM2.5), nitrogen dioxide (NO2), ozone (O-3), and the redox-weighted average of NO2 and O-3 (O-x) 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 mu g/m(3) (hazard ratio, 1.07; 95% confidence interval, 1.06-1.08), NO2 per IQR increase of 119 ppb (1.04; 1.02-1.05), O-3 per IQR increase of 63 ppb (1.04; 1.03-1.04), and O-3 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, O-3, and O-x, 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 adultonset asthma.

Automated summary

The study found positive associations between PM2.5, NO2, O-3, and O-x with COPD, but did not find strong evidence linking these pollutants to adult-onset asthma. Additionally, each IQR increase in pollution exposure yielded excess cases of COPD, with most pollutant-COPD relationships exhibiting supralinear shapes.