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

Abstract

To assess the association between smoking and mortality in patients with chronic obstructive pulmonary disease (COPD) in Sichuan Province, China. 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. 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. 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.