Differential effects of smoking on lung cancer mortality before and after household stove improvement in Xuanwei, China.

BACKGROUND: In Xuanwei County, Yunnan Province, China, lung cancer mortality rates in both males and females are among the highest in China. METHODS: We evaluated differential effects of smoking on lung cancer mortality before and after household stove improvement with chimney to reduce exposure to smoky coal emissions in the unique cohort in Xuanwei, China. Effects of independent variables on lung cancer mortality were measured as hazard ratios and 95% confidence intervals using a multivariable Cox regression model that included separate time-dependent variables for smoking duration (years) before and after stove improvement. RESULTS AND CONCLUSION: We found that the effect of smoking on lung cancer risk becomes considerably stronger after chimney installation and consequent reduction of indoor coal smoke exposure.