Absence of synergism between exposure to asbestos and cigarette smoking in asbestosis

Our plain-English summary of Absence of synergism between exposure to asbestos and cigarette smoking in asbestosis, by J.M. Samet, G.R. Epler, E.A. Gaensler, et al (The American Review of Respiratory Disease, 1979).

The study

• Authors: J.M. Samet, G.R. Epler, E.A. Gaensler, B. Rosner
• Journal: The American Review of Respiratory Disease
• Published: 1979;120(1):75-82
• Cited by: 40 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. 002101).

Abstract

To assess both independent and synergistic effects of exposure to asbestos and cigarette smoking on the development of asbestosis, survey data from 4 groups of workers exposed to asbestos were analyzed with multivariate statistical models. Survey methods were standardized and included for the 383 subjects a respiratory symptoms questionnaire, occupational history, physical examination, pulmonary function testing, and a chest radiograph. Exposure to asbestos and cigarette smoking were assessed by questionnaire. Synergism between the 2 exposures was not present for previously identified manifestations of asbestosis including bilateral fine crackles, clubbing, dyspnea, radiographic abnormality, decreased forced vital capacity, and decreased single-breath diffusing capacity of the lung for CO. However, additive, independent effects of these 2 exposures were present for each of these parameters.

In plain English

The authors tested whether cigarette smoking and asbestos exposure act together more strongly than their separate effects added up (called synergism) in producing signs of asbestosis. They analyzed first-survey data from four groups of asbestos-exposed workers: pipe coverers at shipyard A, pipe coverers and painter-cleaners at shipyard B, asbestos filter makers at factory A, and workers at a fireproofing products plant (factory B). Of 409 subjects, 383 had complete physiologic testing. Asbestos exposure and smoking were assessed by questionnaire. In statistical models, the term measuring the combined effect was not significant in any group for forced vital capacity (FVC), diffusing capacity (DLCO) or chest X-ray score. It was also not significant for crackles, clubbing or shortness of breath. Each exposure instead had separate, additive effects. Asbestos was the main factor in the X-ray score. Smoking was associated with lower DLCO in all four groups. The authors concluded that smoking is not synergistic with asbestos in producing asbestosis. They noted that the exposure measures, obtained by interview, were crude.

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 survey data (questionnaire, occupational history, physical examination, lung function tests, chest X-ray) from four groups of asbestos-exposed workers, using linear and logistic multiple regression to test independent and interaction (synergistic) effects
• Who was studied: Workers from shipyard A (all pipe coverers), shipyard B (pipe coverers plus painter-cleaners who cleaned their work area), factory A (asbestos filter manufacture) and factory B (fireproofing products). Only data from the initial survey were used. Data were available for 409 subjects (98, 128, 89 and 94 by group), of whom 383 had complete physiologic testing. The authors' surveys had been conducted since 1966. Locations are not named.
• Exposure: Occupational asbestos exposure (fiber types not named), indexed by years since first exposure, as reported by questionnaire. Mean years of exposure were 11.6 (shipyard A), 11.0 (shipyard B), 3.4 (factory A) and 7.6 (factory B). Mean years since first exposure were 17.0, 14.6, 15.1 and 12.2 respectively. Cigarette smoking was measured as the log of lifetime pack-years.
• Main results:
  • In each of the four survey groups, the smoking-by-asbestos interaction term was not significant for FVC.
  • For FVC, asbestos exposure had a significant effect in both shipyards and factory B. Smoking had a significant effect only in shipyard B.
  • Smoking was associated with decreased DLCO in all four groups. An additional asbestos effect on DLCO was found only in factory A and factory B. In factory B, the asbestos contribution to explained variance (R2) was nearly twice that of smoking (0.19 vs 0.11).
  • Asbestos exposure was the principal determinant of the chest X-ray score. Smoking had small additive effects, without synergism.
  • When analyzed separately by smoking group (never smokers n = 58, past n = 118, present n = 207), the asbestos coefficients for FVC and DLCO tended to be highest in never smokers. For FVC, they were -0.82 in never, -0.50 in past and -0.52 in present smokers. For DLCO, they were -0.92 in never and -0.85 in past smokers, and not significant in present smokers.
  • For crackles (rales), clubbing and dyspnea, both smoking and asbestos exposure had additive effects. The interaction term was not significant in any analysis.
• The authors' conclusion: The authors concluded that cigarette smoking is not synergistic with asbestos exposure in producing asbestosis, but that the analyses documented adverse effects of each exposure.
• Limitations the authors state:
  • Exposure to asbestos and to cigarette smoke was estimated with crude measures obtained by interview rather than dust measurements. The authors argued this should not bias against detecting synergism.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Synergistic Effect, Occupational History, Chest X-Ray, Bilateral, Clubbing, Dyspnea, Diffusing Capacity (DLCO).

Related studies

• Asbestos and lung cancer: an analysis of the epidemiological evidence on the asbestos-smoking interaction — R. Saracci (1977)
• Asbestosis: interstitial pulmonary fibrosis and pleural fibrosis in a cohort of asbestos insulation workers: influence of cigarette smoking — R. Lilis, I.J. Selikoff, et al. (1986)
• Consensus on synergism between cigarette smoke and other environmental carcinogens in the causation of lung cancer — A.E. Reif, T. Heeren (1999)
• Effects of asbestos and smoking on the levels and rates of change of lung function in a crocidolite exposed cohort in Western Australia — H.S. Alfonso, L. Fritschi, et al. (2004)
• Association of cigarette smoking and asbestos exposure with location and histology of lung cancer — B.W. Lee, J.C. Wain, et al. (1998)
• Cigarette smoking, asbestos, and pulmonary fibrosis — W. Weiss (1971)

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