Air pollution and mortality in patients with chronic obstructive pulmonary disease: a cohort study in South Korea.

Background: Evidence on whether long-term exposure to air pollution increases the mortality risk in patients with chronic obstructive pulmonary disease (COPD) is limited.

Objectives: We aimed to investigate the associations of long-term exposure to particulate matter with diameter <10 µm (PM₁₀) and nitrogen dioxide (NO₂) with overall and disease-specific mortality in COPD patients.

Design: We conducted a nationwide retrospective cohort study of 121,423 adults ⩾40 years diagnosed with COPD during 1 January to 31 December 2009.

Methods: Exposure to PM₁₀ and NO₂ was estimated for residential location using the ordinary kriging method. We estimated the risk of overall mortality associated with 1-, 3-, and 5-years average concentrations of PM₁₀ and NO₂ using Cox proportional hazards models and disease-specific mortality using the Fine and Gray method adjusted for age, sex, income, body mass index, smoking, comorbidities, and exacerbation history.

Results: The adjusted hazard ratios (HRs) for overall mortality associated with a 10 µg/m³ increase in 1-year PM₁₀ and NO₂ exposures were 1.004 [95% confidence interval (CI) = 0.985, 1.023] and 0.993 (95% CI = 0.984, 1.002), respectively. The results were similar for 3- and 5-year exposures. For a 10-µg/m³ increase in 1-year PM₁₀ and NO₂ exposures, the adjusted HRs for chronic lower airway disease mortality were 1.068 (95% CI = 1.024, 1.113) and 1.029 (95% CI = 1.009, 1.050), respectively. In stratified analyses, exposures to PM₁₀ and NO₂ were associated with overall mortality in patients who were underweight and had a history of severe exacerbation.

Conclusion: In this large population-based study of patients with COPD, long-term PM₁₀ and NO₂ exposures were not associated with overall mortality but were associated with chronic lower airway disease mortality. PM₁₀ and NO₂ exposures were both associated with an increased risk of overall mortality, and with overall mortality in underweight individuals and those with a history of severe exacerbation.