Smoking, smoking cessation, and 7-year mortality in a cohort of Thai adults

Background: Smoking is a strong risk factor for mortality in both the developed and the developing world. However, there is still limited research to examine the impact of smoking cessation and mortality in middle-income Southeast Asian populations. Methods: We use longitudinal data from a large Thai cohort of adult Open University students residing nationwide, linked with official death records to assess the association of smoking status and mortality risks during a 7-year follow-up. The log-rank test was used to evaluate the statistical probability of differential survival according to baseline smoking status. Multivariate hazard ratios (HR) were reported for smoking status and all-cause and cause-specific mortality. Results: From 2005 baseline to 2012, current smokers were more likely to die than cohort members who ceased smoking and never smokers (1.9 vs 1.3 vs 0.6 %, p < 0.05). The hazard of all-cause mortality increased with the daily amount of cigarette consumption among both current and former smokers. Cause of death analyses showed that current male smokers had a significantly increased risk of cardiovascular disease related mortality (HR 3.9 [95 % CI 1.8-8.1]). Former male smokers had a moderate increase in risk of dying from cardiovascular diseases compared to never smokers (HR 1.6 [95 % CI 0.7-3.4]). Current male smokers between 2005 and 2009 experienced highest subsequent mortality hazards during the period 2009-2012 compared to never smokers (HR 2.1 [95 % CI 1.4-3.4]). The higher risk of dying reduced if people quit smoking during the 2005-2009 follow-up period (HR 1.5 [95 % CI 0.7-3.3]). Risk for mortality fell even further among long-term quitters (HR 1.4 [95 % CI 0.9-2.2]). Conclusion: Among a large nationwide cohort of Thai adults, current smokers were at a significantly and substantially higher risk of all-cause mortality, especially cardiovascular-related mortality. The higher risk of dying fell if people quit smoking and the risk for mortality was even lower among long-term quitters. Promotion of smoking cessation will contribute substantially to the reduction in avoidable mortality in Thailand.