Estimating health risks in studies of the health effects of asbestos

Our plain-English summary of Estimating health risks in studies of the health effects of asbestos, by P.E. Enterline (The American Review of Respiratory Disease, 1976).

The study

• Author: P.E. Enterline
• Journal: The American Review of Respiratory Disease
• Published: 1976;113(2):175-80
• Cited by: 19 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. 002271).

Abstract

Epidemiologic studies of respiratory cancer hazards associated with asbestos exposure in working populations should provide some estimate not only of whether an excess in cancer exists but of the magnitude of this excess. While most studies seem to be in agreement as to the existence of an excess, there is considerable disagreement as to its magnitude. For 11 studies, estimates of relative risk for respiratory cancer range from about 1.2 to 9.2. Four features of these 11 studies can be identified that account for some of the variation in results: some studies include workers whose exposure to asbestos was too recent to be likely to produce cancer by the end of the follow-up period, and results are diluted by the presence of these workers; in most studies, the wrong population was used for estimating expected numbers of deaths; in some studies, death certificates for the study population were corrected based on a review of other medical records, but then comparisons were made with expected deaths derived from uncorrected death certificates; finally, in most studies, level and duration of exposure is unknown, and this is clearly a factor that determines the magnitude of the respiratory cancer risk. For 6 of the 11 studies it was possible from published material to correct results roughly for the first 3 of these factors and much of the variation disappeared. Problems in the 11 studies reviewed here should be considered in planning and reporting on epidemiologic investigations in the future.

In plain English

The author reviewed 11 prospective U.S. and Canadian studies of respiratory cancer among asbestos-exposed miners, insulators and manufacturing workers. Their relative risks ranged from about 1.2 to 9.2. The author identified four features explaining some of this spread. Some studies included workers whose exposure was too recent to be likely to produce cancer by the end of follow-up. Nearly all U.S. studies took expected deaths from national rather than local rates. Some compared corrected death certificates with expected deaths from uncorrected ones. In most, exposure level and duration were unknown. Roughly recalculating 6 studies from published data, the author stated the adjustments brought the findings much closer together. One Selikoff study went from 9.2 to 6.2 and Wagoner's from 2.8 to 3.6. Among retired asbestos workers, relative risk ranged from 1.2 (under 20 years since first exposure, under 10 mppcf) to 4.7 (30 or more years, over 10 mppcf). The author concluded that, when exposure levels are uncertain, studies should probably include all workers, continue follow-up for a very long time, and report results by years since first exposure.

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: Methodological review of 11 published prospective studies, with rough recalculation of published results for 6 of them and illustrative data from earlier studies
• Who was studied: 11 prospective studies of asbestos-exposed workers (miners, insulators and manufacturing workers) in the United States and Canada, first presented or published 1958 to 1972. Illustrative data came from a cohort of retired asbestos workers and from an early Selikoff insulator study.
• Exposure: Occupational asbestos exposure in mining, insulation work and asbestos product manufacturing. Level and duration were unknown in most studies. Among retired workers, mean dust level was grouped as below or above 10 mppcf.
• Main results:
  • Across the 11 studies, published relative risks for respiratory cancer ranged from about 1.2 to 9.2
  • Some studies included workers whose exposure was too recent to be likely to produce cancer by the end of follow-up
  • In early Selikoff insulator data, observed respiratory cancer deaths rose from 6 (0.8 expected) in 1943 to 1947 to 18 (2.4 expected) in 1958 to 1962. Relative risk was 7.5 in both periods, while absolute risk rose from 2.6 to 7.8 per 1,000 persons.
  • Among retired asbestos workers aged 65 to 74, the respiratory cancer death rate was 2.3 per 1,000 (8 deaths) in 1941 to 1957 and 6.6 per 1,000 (37 deaths) in 1958 to 1969
  • In nearly all U.S. studies, expected respiratory cancer deaths were based on national rather than local mortality
  • In 6 studies that used national death rates for expected deaths, the relative risk observed went up and down with the local respiratory cancer death rate
  • In some studies, corrected death certificates in the study group were compared with expected deaths from uncorrected certificates, which inflated relative risks
  • For 6 studies, relative risks are given three ways: as published, with the death certificate correction removed, and also using local death rates. The figures were Selikoff (6) 9.2, 7.6, 6.2; Enterline 3.0, 3.0, 2.9; Cooper 7.8, 7.8, 6.7; Wagoner 2.8, 2.8, 3.6; Selikoff (14) 8.2, 6.8, 5.5; and Selikoff (16) 5.8, 4.7, 4.7.
  • Among retired asbestos workers with a mean dust level below 10 mppcf, relative risk was 1.2, 1.8 and 2.8 for under 20, 20 to 29, and 30 or more years since first exposure. Above 10 mppcf it was 3.1, 3.6 and 4.7.
• The authors' conclusion: The author concluded that, when exposure levels are uncertain, studies should probably include all workers regardless of years since first exposure, continue follow-up for a very long time, and report results by years since first exposure
• Limitations the authors state:
  • The corrections to published results were only rough
  • The author described whether risk declines 25 years or more after exposure ends as conjectural, with no good epidemiologic observations on it
  • The effects of latent period and of dose expressed as time could not be separated

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Relative Risk, Death Certificate.

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