Low-level air pollution exposure and incidence of chronic obstructive pulmonary disease: the ELAPSE project

Abstract

Background. Air pollution has been suggested as a risk factor for chronic obstructive pulmonary disease (COPD), but evidence is limited. We examined the association between long-term exposure to low-levels of air pollution and incidence of COPD. Methods. Within the multicenter ‘Effects of Low-Level Air Pollution: A Study in Europe’ (ELAPSE) study, we pooled data from three prospective cohorts, from Denmark and Sweden. Hybrid land use regression models (100m resolution) were used to estimate annual mean concentrations of fine particulate matter (PM2.5), nitrogen dioxide (NO2), black carbon (BC), and warm season ozone (O3) in 2010 based on participants’ baseline addresses. Cox proportional hazard models were used to examine the association between air pollution and COPD incidence, defined as first-ever hospital contacts. We also assessed the shape of the concentration-response function with natural cubic splines, and investigated two-pollutant models. Results. Among 98,058 participants, 4,928 (5.0%) developed COPD during a mean follow-up period of 16.6 years. Annual average concentrations of PM2.5, NO2, BC, and O3 were 12.1 μg/m3, 25.1 μg/m3, 1.2 10-5m-1, and 78.1 μg/m3, respectively. The fully adjusted hazard ratios (HRs) and 95% confidential intervals for associations between air pollutants and COPD incidence were 1.17 (1.06-1.29) per 5 µg/m3 for PM2.5, 1.11 (1.06-1.16) per 10 µg/m3 for NO2, 1.11 (1.06-1.15) per 0.5 10-5m-1 for BC, and 0.99 (0.93-1.05) per 10 µg/m3 for O3. Associations persisted in the subset of participants with PM2.5 and NO2 levels below the European limit values. NO2 and BC remained unchanged in two-pollutant models with PM2.5, whereas PM2.5 attenuated to unity. The HR for O3 became positive and significant after adjustment for NO2 or BC. No significant deviation from linearity was observed for any of the associations. Conclusion. Long-term exposure to low-levels of air pollution can lead to the development of COPD, even below current European limit values.