Long-term exposure to air pollution and incidence of chronic obstructive pulmonary disease in Danish Nurse Cohort

<bold>Background:</bold> The toxicity of black carbon (BC) is well known, yet its epidemiological evidence, especially for chronic obstructive pulmonary disease (COPD), remains limited. <bold>Aim:</bold> We examined associations of long-term exposure to BC, fine particulate matter (PM_2.5), and nitrogen dioxide (NO₂) with COPD incidence. <bold>Methods:</bold> We followed 23,820 female nurses aged >44 years from Danish Nurse Cohort, recruited in 1993/1999, until 2018 for first hospital contact for COPD. We estimated residential annual mean air pollution levels from 1980 using the Danish AirGIS modeling system (1km resolution). We used time-varying Cox proportional hazard models to assess the association between 3-year running means of each pollutant and COPD incidence, adjusted for potential covariates. We also explored effect modification by age, lifestyle, socioeconomic factors, and comorbidities including cardiovascular disease (CVD), asthma, diabetes, and pneumonia. <bold>Results:</bold> Over a mean follow-up of 22.8 years, 1,145 nurses developed COPD. Fully adjusted models showed increased COPD risk for BC [hazard ratio (HR): 1.04 (95% confidence interval, 0.98-1.11) per 0.3 μg/m³] and NO₂ [HR: 1.12 (1.04-1.20) per 14.0 μg/m³], but not PM_2.5 [HR: 1.00 (0.88-1.13) per 2.5 μg/m³]. Stronger associations with BC and NO₂ were observed in CVD patients, and for NO₂, in those who were overweight. Due to the high correlation between BC and NO₂ (r =0.89), it is hard to distinguish their independent effects. <bold>Conclusions:</bold> Our findings suggest long-term exposure to combustion-related air pollutants (BC, NO₂) increases COPD risk. Improved exposure assessment is needed to estimate its independent effect on respiratory health.