Risk of lung cancer among Japanese coal miners on hazard risk and interaction between smoking and coal mining

This article examines whether an association is found between lung cancer and coal mining and also whether a correlation is found between smoking and coal mining that relates to the risk of lung cancer in Japanese coal miners. A cohort study was performed in former coal mine areas. The survey was carried out between 1987 and 1989, and was extended in a follow-up period to 1995. 5,818 Japanese males (1,796 coal miners and 4,022 non-coal miners) aged from 40 to 69 yr responded to a mail questionnaire that included occupational history and smoking habits. The data were analysed with Cox's proportional hazards model. Significant differences in hazard ratios for lung cancer were recognized in coal miners with greater than or equal to 15 yr of work (Hazard ratio=2.08, 95% Cl: 1.01-4.27) and current smokers with greater than or equal to 20 cigarettes/day (Hazard ratio=5.41, 95% Cl: 1.26-23.28). As regards the interaction of coal mining and smoking, the hazard ratios were 2.04 (95% Cl: 0.13-32.83) for coal miners who had never smoked, 4.71 (95% Cl: 0.62-35.56) for non-coal miners who were ex-smokers or current smokers, and 6.88 (95% Cl: 0.92-51.65) for coal miners who were ex-smokers or current smokers compared with non-coal miners who had never smoked. The interaction of coal mining and smoking for the risk of lung cancer was likely to be additive rather than synergistic.