Association Between Urban Green Space and Acute Exacerbations of COPD in Korea: A Nationwide Study Using the NHIS-NSC Cohort.

Background: Chronic obstructive pulmonary disease (COPD) is a major health concern in Korea, with a higher burden of acute exacerbations (AE-COPD) compared to Western populations. Environmental exposures such as smoking and air pollution are known contributors, but the impact of urban green space remains underexplored. Methods: We conducted a cohort study using the Korean National Health Insurance Service-National Sample Cohort (2006-2019), including 5,171 patients aged ≥40 years with at least two COPD-related prescriptions within one year. Urban green space exposure was defined as the proportion of designated park area to total district area (2017 KOSIS data) and categorized into quartiles. Cox proportional hazards models estimated associations with AE-COPD and all-cause mortality, adjusting for demographic and clinical factors. Subgroup analyses were conducted by age, sex, income, comorbidities, BMI, smoking, and physical activity. Results: Among 5,171 COPD patients (mean age, 67.5 years; 60.7% male), 1,431 AE-COPD events occurred over 40,486 person-years. AE-COPD incidence declined from 35.4 to 31.3 per 1,000 person-years across green space quartiles. Compared to the lowest quartile, the highest quartile showed a lower AE-COPD risk (adjusted hazard ratio [aHR], 0.75; 95% CI, 0.58-0.96; p for trend = 0.016). Stronger trends were observed in younger adults, men, high-income individuals, and those with comorbidities, though interaction tests were not significant. In a health screening subgroup (n = 3,318), patterns were consistent. No significant association was found with all-cause mortality. Conclusion: Greater urban green space coverage may be associated with reduced AE-COPD risk. However, results should be interpreted with cautiously given model limitations and exploratory nature of subgroup findings.