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.

Objective — To examine associations of incident chronic obstructive pulmonary disease (COPD) and adult-onset asthma with past exposure to fine particulate matter (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 to 85 years, from 2001 to 2015. 3-year moving average of residential exposures to selected pollutants with 1-year lag were estimated during follow-up. We used Cox proportional and Aalen's additive hazards models to quantify the pollution-disease associations, and characterized the shape of these relationships using newly developed non-linear 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 3.4µg/m3 (hazard ratio, 1.07; 95% confidence interval, 1.06-1.08), NO2 per 13.9ppb (1.04; 1.02-1.05), O3 per 6.3ppb (1.04; 1.03-1.04), and Ox per 4.4ppb (1.03; 1.03-1.03). By contrast, we did not find strong evidence linking these pollutants to adult-onset asthma. Additionally, we quantified that each IQR increase in pollution exposure yielded 3.0 (2.4-3.6) excess cases of COPD per 100,000 adults for PM2.5, 3.2 (2.0-4.3) for NO2, 1.9 (1.3-2.5) for O3, 2.3 (1.7-2.9) for Ox. Furthermore, most pollutant-COPD relationships exhibited supralinear shapes.

Conclusions — Air pollution was associated with higher incidence of COPD, but not adult-onset asthma.