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 (PM(10)) and nitrogen dioxide (NO(2)) 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 PM(10) and NO(2) 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 PM(10) and NO(2) 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/m(3) increase in 1-year PM(10) and NO(2) 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/m(3) increase in 1-year PM(10) and NO(2) 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 PM(10) and NO(2) 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 PM(10) and NO(2) exposures were not associated with overall mortality but were associated with chronic lower airway disease mortality. PM(10) and NO(2) exposures were both associated with an increased risk of overall mortality in underweight individuals and those with a history of severe exacerbation.