A study of the mortality of workers in an asbestos factory

Our plain-English summary of A study of the mortality of workers in an asbestos factory, by M.L. Newhouse (British Journal of Industrial Medicine, 1969).

The study

• Author: M.L. Newhouse
• Journal: British Journal of Industrial Medicine
• Published: 1969;26(4):294-301
• Cited by: 79 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M nos. 001404, 002472).

Abstract

Newhouse, M. L. (1969).Brit. J. industr. Med.,26, 294-301. A study of the mortality of workers in an asbestos factory. A cohort study of over 4,500 male workers employed at an asbestos factory making both textiles and insulation materials is described. The main analysis of the mortality of workers employed between April 1, 1933, the date of the implementation of the Asbestos Regulations, and May 1, 1964. The analysis was made in relation to job, length of exposure, and length of follow-up after first exposure. There was no significant difference between the number of deaths occurring in the factory population and the national figures, until an interval of 16 years or longer had elapsed from first exposure in the factory. There were 1,160 men who fulfilled this criterion. In this group there was no excess mortality among those who worked in jobs where exposure was low or moderate, but among those with jobs which entailed heavy exposure there was a significant excess of deaths from cancer of the lung and pleura, and cancer of other sites, in men with a total period of employment in the factory of less than two years, as well as with those who worked for longer. Excess mortality from respiratory disease was observed only among severely exposed workers with long service.

In plain English

This cohort study followed male workers at an asbestos textile and insulation factory using amosite, crocidolite and chrysotile. The main analysis covered 4,695 men who worked only after the Asbestos Regulations took effect on April 1, 1933, followed to May 1, 1964. Observed deaths were compared with those expected from England and Wales death rates, and jobs were graded by severity of dust exposure. In the first years after starting work, fewer deaths occurred than expected. Among men followed 16 years or more (464 with low to moderate, 696 with severe exposure), the low to moderate group showed no excess deaths. Severely exposed men employed under two years had a statistically significant excess of deaths from cancer of the lung and pleura and from other cancers; 17 of their 34 deaths were from cancer. The article's discussion and its Table 7 disagree on how many cancer deaths were expected in this group. Severely exposed men employed longer had excess deaths from these cancers and from respiratory disease; four were certified as asbestosis. The author noted that smoking habits were unknown.

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: Retrospective cohort mortality study comparing observed deaths with expected deaths calculated from death rates for England and Wales
• Who was studied: Male workers at an asbestos factory. The main group was 4,695 men who worked only after April 1, 1933, of whom all but 5% were traced, followed to May 1, 1964. A further 140 men worked both before and after that date. A group of 438 men who worked only before 1933 was excluded because its follow-up was too incomplete.
• Exposure: Asbestos dust in a factory making textiles and insulation materials, where amosite, crocidolite and chrysotile were all used. Jobs were graded from 1 (very low) to 6 (severe). Grades 1 to 3 were analysed together as low to moderate exposure, and grades 5 and 6 together as severe exposure. Laggers, mates and labourers (grade 4) were considered separately.
• Main results:
  • Study 1 (3,268 men, deaths from the 2nd to the 4th year after entering the survey): men with low to moderate exposure had 14 deaths against 19.2 expected, and men with severe exposure had 10 deaths against 14.6 expected.
  • Study 3 included men followed for at least 16 years since entering the factory: 464 with low to moderate exposure and 696 with severe exposure (375 in grade 5 jobs and 321 in grade 6).
  • Study 3: men with low to moderate exposure showed no excess mortality, whether employed less than or more than two years.
  • Study 3, severely exposed men employed less than two years: there was a statistically significant excess of deaths from cancers of the lung and pleura and from cancers of other sites.
  • Study 3, severely exposed men employed less than two years: the discussion states that 17 of 34 deaths were due to cancer. It prints the expected number as '3 3', apparently 3.3 with the decimal point lost in scanning.
  • Table 7, which the discussion cites, gives different expected figures for the same group: 8 lung and pleura cancer deaths against 1.6 expected (printed as '16'; Table 9's subgroup figures of 1.0 and 0.6 confirm 1.6), and 9 other-cancer deaths against 2.7 expected. Added together, these give 4.3 expected cancer deaths. That total is worked out here from Table 7 and is not stated in the article.
  • Among the short-service severely exposed men, the significant excess of lung and pleura cancer and other cancers occurred in the grade 5 group but not in the grade 6 group.
  • Study 3, severely exposed men employed more than two years: there was excess mortality from cancer of the lung and pleura, cancer of other sites, and respiratory disease. Four of the respiratory deaths were certified as asbestosis.
  • Among longer-service severely exposed men in Study 3, respiratory disease deaths were concentrated in grade 5: nine observed against 1.8 expected, P less than 0.001.
  • Significant excesses of deaths from cancer of the lung and pleura, other cancers and respiratory diseases appeared in certain groups after 17 to 21 years of follow-up. The author suggested this means the latent period may be less than 20 years in these workers.
  • Among 623 men on insulating contracts (laggers' mates and labourers) followed 5 to 16 years, there were six deaths. Three were from carcinoma of the lung and pleura, against 0.38 expected (p less than 0.001).
  • Among the 140 men who worked both before and after April 1, 1933, those with more than two years' service had a statistically significant excess of lung and pleura cancer deaths in both the low to moderate and the severe exposure groups.
  • In the group who worked before and after 1933, 11 of the severely exposed men and 3 of those with lesser exposure were certified as dying from asbestosis.
• The authors' conclusion: The author concluded that there was a marked contrast between the mortality of men graded as having low to moderate exposure and that of men graded as severely exposed, with no suggestion of an adverse effect on mortality in the low to moderate group.
• Limitations the authors state:
  • The workers' smoking habits were unknown because no direct contact was made with any worker.
  • Some workers may have been categorized by a job held for only a small part of their total service.
  • Fitters and maintenance men, whose exposure may have varied, were difficult to grade.
  • Men who worked only before the 1933 regulations were excluded because their follow-up was too incomplete.
  • Conditions in the factory before the regulations could not be assessed, which affects interpretation of the group who worked before and after 1933.

Topics

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

Medical terms in this study, explained in our Lexicon: Cohort Study, Pleura.

Related studies

• Predictions of mortality from mesothelial tumours in asbestos factory workers — M.L. Newhouse, G. Berry (1976)
• Combined effect of asbestos exposure and smoking on mortality from lung cancer in factory workers — G. Berry, M.L. Newhouse, et al. (1972)
• Mortality of factory workers in east London 1933-80 — M.L. Newhouse, G. Berry, et al. (1985)
• Combined effect of asbestos and smoking on mortality from lung cancer and mesothelioma in factory workers — G. Berry, M.L. Newhouse, et al. (1985)
• Mortality from all cancers of asbestos factory workers in east London 1933-80 — G. Berry, M.L. Newhouse, et al. (2000)
• Mortality experience of amosite asbestos factory workers: dose-response relationships 5 to 40 years after onset of short-term work exposure — H. Seidman, I.J. Selikoff, et al. (1986)

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