Smoking cessation and mortality among middle-aged and elderly Chinese in Singapore: the Singapore Chinese Health Study

OBJECTIVE: This study determines if recent smoking cessation, compared with long-term cessation, can reduce mortality risk associated with smoking. METHODS: Data from the Singapore Chinese Health Study, a cohort study of middle-aged and elderly Chinese in Singapore, were analysed (n=48 251). Smoking status was evaluated at recruitment between 1993 and 1998 and reassessed between 1999 and 2004. Participants were classified as never-smokers, long-term quitters (quit before recruitment, mean 17.0 years), new quitters (quit between recruitment and second interview, mean 4.3 years) and current smokers. Mortality was ascertained by linkage with the nationwide death registry. RESULTS: After a mean follow-up of 8.1 years, 6003 deaths had occurred by 31 December 2009. Compared with current smokers, the adjusted HR (95% CI) for total mortality was 0.84 (0.76 to 0.94) for new quitters, 0.61 (0.56 to 0.67) for long-term quitters and 0.49 (0.46 to 0.53) for never-smokers. New quitters had 24% reduction in lung cancer mortality (HR: 0.76, 95% CI 0.57 to 1.00) and long-term quitters had 56% reduction (HR: 0.44, 95% CI 0.35 to 0.57). Risk for coronary heart disease mortality was reduced in new quitters (HR: 0.84, 95% CI 0.66 to 1.08) and long-term quitters (HR: 0.63, 95% CI 0.52 to 0.77), although the result for new quitters was of borderline significance due to relatively small number of cardiovascular deaths. Risk for chronic pulmonary disease mortality was reduced in long-term quitters but increased in new quitters. CONCLUSION: Significant reduction in risk of total mortality, specifically for lung cancer mortality, can be achieved within 5 years of smoking cessation.