Possible effects on occupational lung cancer from smoking related changes in the mucus content of the lung.

A number of recent epidemiological studies of lung cancer among occupations that expose workers to dusts or toxic aerosols have reported a larger prevalence of lung cancer among non-smoking than among smoking workers. One recent study using Beagle dogs has also reported significantly fewer respiratory tumors among animals exposed to radon, radon daughters, uranium dust and tobacco smoke than among animals exposed similarly except for tobacco smoke. The evidence is summarized here that the increased mucus in the lungs of smokers may help in the elimination of dust and toxic substances by facilitating migration of particles and aerosols and possibly also adding protection by thickening of the mucus layer. Recent developments in use of in vivo magnetometric measurements of dust content of workers' lungs in fact indicate that lungs of chronically exposed miners and millers contain less dust if they smoke than if they do not. The hypothesis that increasing mucus in the lung of exposed workers may protect them against lung disease now needs experimental verification in appropriate animal studies. If protective qualities of lung mucus are verified, means need to be explored that will increase mucus flow in non-smoking (and smoking) workers exposed to respiratory hazards.