Interaction of asbestos, age, and cigarette smoking in producing radiographic evidence of diffuse pulmonary fibrosis.

The study of 3,472 chest x-rays from four populations with different levels of exposure to asbestos and with different cigarette smoking histories shows that smoking in the general population does not produce pulmonary fibrosis recognizable on chest radiography. In the general population of Michigan, the prevalence of a radiographic pattern of fibrosis was 0.5 percent in men and 0.0 percent in women. In a Long Beach, California census tract population, the prevalences were 3.7 percent for men and 0.6 percent for women. Similarly, cigarette smoking does not enhance fibrosis when the exposure to asbestos has been as light as that in households of shipyard workers. Asbestosis was recognized in 6.6 percent of 137 shipyard workers' wives who have never smoked and 7.6 percent of 132 who had ever smoked. Cigarette smoking and asbestos appear to be synergistic in those occupationally exposed to asbestos (as insulators), since 7.2 percent of 97 nonsmokers and 20.5 percent of 316 ever-smokers showed fibrosis. This apparent synergy was also found in shipyard workers up to age 70 with 31 percent of nonsmokers and 43.3 percent of ever-smokers having fibrosis. There were increases of approximately 10 percent in the prevalence of fibrosis in cigarette smokers and nonsmokers for each decade after age 40.