Long-term air pollution and road traffic noise exposure and COPD: the Danish Nurse Cohort

Background: While air pollution has been linked to the development of chronic obstructive pulmonary disease (COPD), evidence on the role of environmental noise is just emerging. We examined the associations of long-term exposure to air pollution and road traffic noise with COPD incidence. Methods: We defined COPD incidence for 24,538 female nurses from the Danish Nurse Cohort (age > 44 years) as the first hospital contact between baseline (1993 or 1999) and 2015. We estimated residential annual mean concentrations of particulate matter with diameter < 2.5 µm (PM_2.5) since 1990 and nitrogen dioxide (NO₂) since 1970 by the Danish DEHM/UBM/AirGIS modeling system, and road traffic noise (L_den) since 1970 by the Nord2000 model. Time-varying Cox regression models were applied to assess the associations of air pollution and road traffic noise with COPD incidence. Results: 977 nurses developed COPD during 18.6 years’ mean follow-up. We observed associations with COPD for all three exposures with hazard ratios (HRs) and 95% confidence intervals (CIs) of 1.19 (1.01, 1.41) per 6.26 µg/m³ for PM_2.5, 1.13 (1.05, 1.20) per 8.19 µg/m³ for NO₂, and 1.15 (1.06, 1.25) per 10 dB for L_den. Associations with NO₂ and L_den attenuated slightly after adjustment for each other, but were robust to adjustment for PM_2.5. Associations with PM_2.5 were attenuated to null after adjustment for either NO₂ or L_den. No potential interaction effects was observed between air pollutants and noise. Conclusions: Long-term exposure to air pollution, especially traffic-related pollutant, and road traffic noise were independently associated with COPD.