The degree of roentgenographic parenchymal opacities attributable to smoking among asbestos-exposed subjects

Our plain-English summary of The degree of roentgenographic parenchymal opacities attributable to smoking among asbestos-exposed subjects, by S. Barnhart, M. Thornquist, G.S. Omenn, et al (The American Review of Respiratory Disease, 1990).

The study

• Authors: S. Barnhart, M. Thornquist, G.S. Omenn, G. Goodman, P. Feigl, L. Rosenstock
• Journal: The American Review of Respiratory Disease
• Published: 1990;141(5 Pt 1):1102-6
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 003671).

Abstract

Considerable controversy surrounds the question of whether cigarette smoking has the potential to increase the prevalence of small opacities on chest roentgenographs among asbestos-exposed workers. To compare the relative contribution of smoking with other predictors of the presence of roentgenographic small opacities, we examined 661 men enrolled in a double-blind, randomized trial designed to assess the efficacy of vitamin A and beta-carotene in the prevention of lung cancer among workers with heavy occupational asbestos exposure. Subjects in the study population had a mean latency of 35 yr from first asbestos exposure and a mean of 28 yr in their trade. The prevalence of roentgenographic abnormalities consistent with asbestos exposure was 26% for pleural abnormalities alone, 10% for parenchymal abnormalities alone, and 20% for pleural and parenchymal abnormalities together. We investigated occupation, age, latency from first asbestos exposure, and smoking status as predictors of roentgenographic small opacities. Smoking history, independent of latency, contributed to the prevalence and extent of small opacities, but its effect was less than that of latency. We conclude, that in the setting of heavy occupational exposure to asbestos, cigarette smoking confers added risk for the development of roentgenographic small opacities.

In plain English

The authors examined chest X-rays taken when 661 men with heavy occupational asbestos exposure joined a Seattle trial testing vitamin A and beta-carotene for lung cancer prevention (1985 to 1988). All had worked at least 5 years in high-risk trades such as asbestos insulation, pipefitting and shipyard work. On average, 35 years had passed since first exposure. Of 656 men with complete data, 44% had normal X-rays, 26% had pleural abnormalities only, 10% had small lung-tissue (parenchymal) opacities only, and 20% had both. In statistical models, the presence and degree of small opacities were associated with time since first exposure, age, occupation, nonwhite race and pack-years of smoking. For presence, smoking's p value was 0.06. For a typical man (age 58, 27 pack-years), smoking accounted for an estimated 0.16 of a minor category on the ILO X-ray scale, against 0.67 for time since first exposure. Never smokers had risk similar to smokers with few pack-years. The authors concluded that smoking contributes to small opacities in asbestos-exposed men, with about one-fourth the effect of asbestos exposure measured by time since first exposure. They noted that their model left a substantial portion of the variation unexplained.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Analysis of entry examinations (questionnaire, chest X-ray, spirometry) of men enrolled in a placebo-controlled, double-blind, randomized chemoprevention trial (Seattle Asbestos Chemoprevention Study, part of CARET), using logistic and linear regression
• Who was studied: 661 of 816 consecutive men enrolled in Seattle between June 1985 and October 1988, aged 45 to 74 at entry. Five were excluded for missing data, leaving 656 in the X-ray table. Mean age 58 (plus or minus 8) years. 95% white, 2% black. 16% never smokers, 62% former smokers, 21% current smokers. Recruited through workers' compensation systems, physicians, unions, the US Navy and attorneys.
• Exposure: Occupational asbestos exposure: at least 5 years in a high-risk trade (asbestos insulators, plumbers and pipefitters, shipyard electricians, shipyard boilermakers, shipscalers, riggers, sheetmetal workers, plasterers) completed at least 10 years before entry. Mean 35 (plus or minus 9) years since first exposure and mean 28 (plus or minus 10) years in trade. Fiber types were not reported. Smoking was measured in pack-years: mean 27 (plus or minus 23) for the whole cohort.
• Main results:
  • X-ray findings in the whole cohort (656 men): 288 (44%) normal, 169 (26%) pleural abnormalities alone, 64 (10%) parenchymal abnormalities, and 135 (20%) both pleural and parenchymal abnormalities consistent with asbestos exposure.
  • In logistic regression, an excess of small opacities (ILO profusion 1/0 or more) was associated with pack-years of smoking (p = 0.06), nonwhite race (p = 0.02), latency (p = 0.02), occupation (p = 0.01) and age (p = 0.04).
  • Never smokers had risk similar to smokers with few pack-years, and no statistically significant benefit of quitting smoking was found.
  • Among occupations, asbestos insulators had the greatest odds ratio of excess small opacities.
  • In linear regression on the ILO profusion score, the estimated contributions were 0.19 per decade of latency, 0.23 per decade of age, and 0.06 per 10 pack-years of smoking, in minor ILO profusion categories.
  • For the 'average' subject (age 58, latency 35 years, 27 pack-years), these variables accounted for estimated increases of 1.3 ILO minor categories for age, 0.67 for latency and 0.16 for smoking.
  • Models using self-reported levels of exposure and respirator use found no additional benefit beyond latency as a measure of exposure.
  • Rales were present in 25% overall, and in 18%, 37%, 50% and 50% of men in ILO major categories 0, 1, 2 and 3 respectively. Spirometry was normal in 54%, obstructive in 24%, restrictive in 11% and mixed in 12%.
• The authors' conclusion: The authors concluded that cigarette smoking contributes to the development of X-ray small opacities among asbestos-exposed subjects. In their 'average subject', the effect of smoking was one-fourth that of asbestos exposure defined by latency. They added that smoking has not consistently been shown, independent of asbestos, to be an important contributor.
• Limitations the authors state:
  • Respondent bias from the recruitment strategy and eligibility criteria may limit generalizability to other asbestos-exposed cohorts.
  • Small-opacity profusion was mostly in the lower ILO categories.
  • Latency (years from first exposure) may not reflect the intensity and duration of exposure.
  • The linear regression model had an R-squared of 0.12, so a substantial portion of the variance was not explained.
  • Because age and years since first exposure were highly collinear, their separate effects were difficult to estimate.
  • X-ray small opacities may not correlate perfectly with interstitial fibrosis seen under the microscope, and no biopsy specimens were available.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Asbestos Exposure, Latency, Occupational Exposure.

Related studies

• Smoking and roentgenographic opacities in US Navy asbestos workers — A.M. Ducatman, B.F. Withers, et al. (1990)
• The relation among pulmonary function, chest roentgenographic abnormalities, and smoking status in an asbestos-exposed cohort — L. Rosenstock, S. Barnhart, et al. (1988)
• Radiographic abnormalities in asbestos insulators: effects of duration from onset of exposure and smoking. Relationships of dyspnea with parenchymal and pleural fibrosis — R. Lilis, A. Miller, et al. (1991)
• Cigarette smoking and small irregular opacities — W. Weiss (1991)
• Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers — A. Kraut, J. Godbold, et al. (1989)
• Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers — E. Hnizdo, G.K. Sluis-Cremer (1988)

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