Long-term exposure to air pollution and risk of adult-onset asthma and chronic obstructive pulmonary disease: Danish nationwide cohort study

Abstract

Rationale: Long-term exposure to air pollution contributes to chronic respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). While the effect of fine particulate matter (PM2.5) and nitrogen dioxide (NO2) are supported by evidence, the contribution of black carbon (bc), a combustion-related pollutant, remains unclear. Objectives: To investigate associations of long-term exposure to bc as well as PM2.5 and NO2 with incidence of adult-onset asthma and COPD in Denmark. Methods: We followed 3.2 million Danish residents aged 30 years or older on January 1, 2000 until December 31, 2018, for incidence of asthma and COPD (first hospital contact), and combined incidence (first prescription for obstructive airway disease [OAD] medication). Annual mean concentrations of air pollutants were estimated using European-wide hybrid land-use regression models. Cox proportional hazard models were used with adjustment of demographic, socioeconomic factors, smoking, and body mass index. Results: During 50.7, 50.4, and 44.4 million person-years of follow-up, 52 648 participants developed asthma, 146 269 developed COPD, and 393 211 were prescribed OAD medication, respectively. An interquartile range increase of 2.0 and 10.3 µg/m3, and 0.5 × 10−5/m in PM2.5, NO2, and bc, respectively, were associated with higher risks of asthma incidence (hazard ratio: 1.10 [95% confidence interval: 1.08, 1.13]; 1.16 [1.13, 1.19]; 1.17 [1.14, 1.20]), COPD incidence (1.04 [1.02, 1.05]; 1.05 [1.03, 1.07]; 1.06 [1.04, 1.08]), and OAD medication (1.02, [1.01, 1.03]; 1.05 [1.03, 1.06]; 1.03 [1.02, 1.05]). The observed association with PM2.5 were attenuated or became null after adjusting for NO2 or bc, while those with NO2 or bc remained robust after adjusting for PM2.5. Conclusion: In a large Danish nationwide analysis, air pollution is an important predictor for adult-onset asthma and COPD. Our findings suggest that the relevance of pollutants originating from combustion sources, as reflected by the association with bc and NO2, may contribute importantly to these respiratory outcomes. Targeted actions to reduce combustion-related emissions, including those leading to bc formation, may further help decrease the burden of chronic respiratory diseases.