Long-term exposure to particulate matter and COPD mortality: Insights from causal inference methods based on a large population cohort in southern China

Background: Evidence of the association between long-term exposure to particulate matter (PM) and chronic obstructive pulmonary disease (COPD) mortality from large population-based cohort study is limited and often suffers from residual confounding issues with traditional statistical methods. We hereby assessed the casual relationship between long-term PM (PM_2.5, PM₁₀ and PM_10–2.5) exposure and COPD mortality in a large cohort of Chinese adults using state-of-the-art causal inference approaches. Methods: A total of 580,757 participants in southern China were enrolled in a prospective cohort study from 2009 to 2015 and followed up until December 2020. Exposures to PM at each residential address were obtained from the Long-term Gap-free High-resolution Air Pollutant Concentration dataset. Marginal structural Cox models were used to investigate the association between COPD mortality and annual average exposure levels of PM exposure. Results: During an average follow-up of 8.0 years, 2250 COPD-related deaths occurred. Under a set of causal inference assumptions, the hazard ratio (HR) for COPD mortality was estimated to be 1.046 (95 % confidence interval: 1.034–1057), 1.037 (1.028–1.047), and 1.032 (1.006–1.058) for each 1-μg/m³ increase in annual average concentrations of PM_2.5, PM₁₀, and PM_10–2.5 respectively. Additionally, the detrimental effects appeared to be more pronounced among the elderly (age ≥ 65) and inactive participants. The effect estimates of PM_2.5, PM₁₀, and PM_10–2.5 tend to be greater among participants who were generally exposed to PM₁₀ concentrations below 70 μg/m³ than that among the general population. Conclusion: Our results support causal links between long-term PM exposure and COPD mortality, highlighting the urgency for more effective strategies to reduce PM exposure, with particular attention on protecting potentially vulnerable groups.