Smoking and mortality risk in COPD patients: a prospective cohort study in Sichuan, China.

Purpose: To assess the association between smoking and mortality in patients with chronic obstructive pulmonary disease (COPD) in Sichuan Province, China. Methods: Data concerning COPD patients in Pengzhou, Sichuan was collated from the China Kadoorie Biobank (CKB). COPD was defined as post-bronchodilator forced expiratory volume in 1 s/forced vital capacity of <70%. The relationship between smoking and mortality was evaluated by Cox proportional hazards regression. Results: Eight thousand five hundred one COPD patients, aged 30-79 years, were enrolled enabling analysis of 85,600 person-years of follow-up data (mean follow-up: 10.07 years). Two thousand deaths occurred during the period of investigation, including 665 from COPD and 1,116 from cardiovascular disease (CVD). Ex-smokers were at higher risk of both all-cause mortality [hazard ratio (HR) 1.56; 95% confidence interval (CI) 1.36-1.80], COPD (HR 2.24; 95% CI 1.80-2.80) and CVD mortality (HR 1.54; 95% CI 1.28-1.85) than those who had never smoked. An increased duration of smoking was associated with higher risk of death. A dose-response relationship was observed. Patients who smoked > 20 g tobacco/day had 35% higher all cause, 66% higher COPD and 34% higher CVD mortality risk. Those with cumulative exposures ≥ 250,000 g had the highest risks of all outcomes. Earlier age of smoking onset and oral only smoke intake (as opposed to lung inhalation) were also linked to greater mortality risk. Conclusion: Smoking was an independent risk factor for COPD-specific, CVD and all-cause mortality in COPD patients from Sichuan with higher tobacco consumption giving a stronger association.