Background and objective: Although the association between COPD and smoking status (non-smoking, ex-smoking and current smoking) and indoor air pollution in Chinese populations is well established, the link between COPD and the number of cigarettes smoked has not been examined. This study investigated the relationship between the total amount of cigarettes smoked (TACS) and indoor air pollution, with the risk of COPD among urban and rural Chinese adults.
Methods: A nested case-control study was performed using data collected in a large community survey (N = 29 319) conducted between October 2000 and March 2001 in Nanjing, China. The exposure to indoor respiratory pollutants of cooking and heating materials and to passive cigarette smoke was compared in patients diagnosed with COPD (n = 1743) and controls matched for age, gender and residence (n = 1743).
Results: The smoking rate among COPD patients was significantly higher than that among the controls. After controlling for possible confounders, the adjusted odds ratios for COPD increased across TACS tertiles: from lower (OR = 1.40, 95% confidence interval (CI): 1.09-1.79), to middle (OR = 1.55, 95% CI: 1.21-1.99), and upper (OR = 1.77, 95% CI: 1.37-2.29). Among smokers, women were significantly more likely to develop COPD than men (OR = 1.20, 95% CI: 1.02-1.41). There were no significant associations between COPD and domestic fuels used, kitchen ventilation or passive smoking. Heating in winter with coal was weakly but positively linked with COPD among non-smokers overall, among women non-smokers, and specifically for women living in urban as well as rural areas.
Conclusions: A clear dose-response relationship exists between cigarette smoking and COPD; compared with men, women smokers were more susceptible to COPD. Exposure to other respiratory pollutants in the home was not significantly associated with the diagnosis of COPD.