Joint association of cigarette smoking and PM 2.5 with COPD among urban and rural adults in regional China.

BACKGROUND Cigarette smoking and PM2.5 are important risk factors of Chronic Obstructive Pulmonary Disease (COPD). However, the joint association of cigarette smoking and PM2.5 with COPD is unknown. METHODS A community-based study was conducted among urban and rural adults aged 40 + years between May and December of 2015 in Jiangsu Province, China. The outcome variable was spirometry-defined COPD. Explanatory measures were smoking status (non-smokers or smokers) and PM2.5 exposure [low level (< 75 μg/m3) or high level (≥ 75 μg/m3)]. Mixed-effects logistic regression models were applied to calculate the odds ratio (OR) and 95% confidence interval (CI) to investigate the associations of cigarette smoking and PM2.5 with COPD. RESULTS The prevalence of COPD was 11.9% (95% CI = 10.9%, 13.0%) within the overall 3407 participants in this study. After adjustment for potential confounders and community-level clustering effect, smokers tended to develop COPD relative to non-smokers (OR = 2.46, 95% CI 1.76, 3.43), while only smokers exposed to high level PM2.5 were more likely to experience COPD (OR = 1.36; 95% CI 1.01, 1.83) compared to their counterparts exposed to low level PM2.5. Meanwhile, compared to non-smokers who exposed to low level PM2.5, non-smokers who exposed to high level PM2.5 (OR = 1.10, 95% CI 0.74, 1.64), smokers who exposed to low (OR = 2.22, 95% CI 1.51, 3.27) or high level PM2.5 (OR = 3.14, 95% CI 2.15, 4.59) were, respectively, more like to develop COPD. CONCLUSIONS Cigarette smoking was positively associated with COPD among overall participants, while PM2.5 was in positive relation to COPD among smokers only. Moreover, cigarette smoking and PM2.5 might have an additive effect on the risk of COPD among adult smokers aged 40 years or older in China.