Distribution of silicotic collagenization in relation to smoking habits

Controversy regarding the association between silicosis and lung cancer has been clouded by the fact that studies examining this association generally do not include information on smoking. A causal association between smoking and silicosis would seriously confound the association between silicosis and lung cancer. The current analysis assessed the association between silicosis and smoking using data on deceased white gold miners who underwent postmortem examination between 1976 and 1981. Smoking histories and exposure information were available. A subset analysis in a group of deceased miners for whom more detailed smoking and exposure information was available confirmed the findings of the larger analysis. Both analyses showed a slight inverse relationship between smoking and silicotic collagenization of the parenchyma and a stronger negative relationship between smoking and silicotic collagenization of the pleura, controlling for age and cumulative exposure to silica dust. No association between silicotic collagenization of the hilar glands and smoking was detected. The data should not be construed as advocating that workers exposed to silica dust should smoke. The hazards of cigarette smoking are likely to far outweigh the hazards of silicosis. The data suggest that the lack of smoking histories in studies of the association between silicosis and lung cancer probably does not seriously confound risk estimates. The distribution of silicotic collagenization in the lungs of smokers and nonsmokers is consistent with enhanced mucus interception, more central deposition in the lungs, and proportionally more lymphatic clearance to the hilum (as opposed to the pleura) of silica particles in smokers compared to nonsmokers.