Association between smoking and deaths due to colorectal malignant carcinoma: a national population-based case-control study in China

Background: This study explored the association between smoking and colorectal malignant carcinoma (CRC) in the Chinese population at the national level for the first time. Methods: In the China Nationwide Retrospective Mortality Survey conducted during 1989-1991, 12 942 CRC cases among 1 136 336 all-cause deaths aged >= 30 years were randomly assigned 25 884 control interviews from 325 255 surviving spouses of all-cause deaths across 103 urban and rural areas. Results: Compared with non-smokers, smoking significantly increased the risk of CRC-specific mortality by 9.8% (odds ratio (OR) = 1.098, 95% confidence interval (CI) = 1.046-1.153) adjusted for sex, age, and residence. There were significant dose-response relationships between smoking and CRC, such as smoking years, cigarettes smoked daily, and age at onset of smoking. Long-term heavy smokers aged >= 50 years with >= 30 smoking years and >= 20 cigarettes daily had an excess risk of CRC deaths of 30.2% (OR = 1.302, 95% CI = 1.214-1.397). The strongest association between these smoking variables, such as long-term heavy smokers (OR = 1.604, 95% CI = 1.341-1.919), and CRC was observed among rural men. Conclusions: Quitting smoking at any time would likely be beneficial to CRC prevention. Long-term heavy smokers and rural men should be viewed as special targets for smoking prevention and cessation programs.