Survival in cohorts of asbestos cement workers and controls

Our plain-English summary of Survival in cohorts of asbestos cement workers and controls, by M. Albin, V. Horstmann, K. Jakobsson, et al (Occupational and Environmental Medicine, 1996).

The study

• Authors: M. Albin, V. Horstmann, K. Jakobsson, H. Welinder
• Journal: Occupational and Environmental Medicine
• Published: 1996;53(2):87-93
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To measure the impact on survival of being exposed to asbestos cement dust.

Methods: Survival of 866 asbestos cement workers and 755 controls was studied with Cox's proportional hazards regression models with age as the basic time variable. The effect of cumulative exposure up to the age of 40 was investigated in an internal analysis of 635 asbestos cement workers who had dose estimates.

Results: The death risk was higher for the asbestos cement workers than for the controls with a hazard ratio (HR) of 1.15 (95% confidence interval was 1.00 to 1.31). The increased risk found seemed to be confined to the period 20-40 years from start of employment. The estimates of the cohort effect were almost unaffected by adjustment for smoking habits. The estimates of the exposure effect rose with increasing dose (< 4 fibre-years/ml (f-y/ml): HR = 1.00, 4-9.9 f-y/ml: HR = 1.06, > or = 10 f-y/ml: HR = 1.35, for workers with at least five years of employment), and were higher when restricted only to deaths from malignant or non-malignant respiratory disease. However, none of the point estimates were significantly increased. Median age at death was two years lower in the high than in the low, exposure group.

Conclusions: The results indicate that even a moderate asbestos exposure may shorten the median duration of life in an exposed population. Compared with the estimated effect on duration of life from ever being a smoker, that of ever being an asbestos cement worker was less, although that of having a high exposure was similar.

In plain English

This Swedish cohort study compared survival of 866 male asbestos cement workers and 755 male controls from other regional plants. Follow-up ran from age 40 (not before one year of employment or February 1946; 1952 at one control plant) to death, emigration, loss to registration or 30 June 1991. Chrysotile was the main fiber, with small amounts of amosite and crocidolite. Adjusted for smoking, workers had a higher death risk than controls (hazard ratio 1.16, 95% confidence interval 1.01 to 1.33). This excess seemed confined to 20 to 40 years after first exposure. Respiratory diseases caused 85 deaths among workers and 39 among controls; ten worker deaths were mesotheliomas. Among 635 workers with dose estimates, the highest dose group had higher risk estimates, none statistically significant. Among 331 workers employed at least five years, Kaplan-Meier median age at death was 75.1 (95% confidence interval 70.0 to 77.4) in the high and 78.8 (71.5 to 80.8) in the low exposure group. The authors concluded that even moderate asbestos exposure may shorten median life span. They noted wide confidence intervals and incomplete smoking data.

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: Cohort study comparing survival of asbestos cement workers with control workers (Cox regression and Kaplan-Meier analyses), plus an internal dose-response analysis within the asbestos cement cohort
• Who was studied: 866 male Swedish blue collar workers from an asbestos cement plant that operated 1907-77, and 755 male industrial workers from five plants in the same region (a slaughter house, a fertiliser plant, a sugar refinery, a textile plant and a metal industry). Both groups were restricted to workers employed at least one year, alive at age 40 and in employment after February 1946. The internal analysis covered 635 asbestos cement workers with dose estimates. Follow-up started at age 40, but not earlier than one year after the start of employment. In the comparison with controls it also started no earlier than February 1946 (1952 at one control plant). It ended at death, emigration, loss to national registration, or 30 June 1991, whichever came first.
• Exposure: Asbestos cement dust, mainly chrysotile with small amounts of amosite and crocidolite. Median estimated intensity was 1.1 f/ml and the arithmetic mean was 1.4 f/ml. In the internal analysis, cumulative dose up to age 40 was grouped as under 4, 4 to 9.9, and 10 or more fibre-years/ml.
• Main results:
  • Asbestos cement workers had a higher death risk than controls in the entire cohorts, with smoking taken into account: HR 1.16 (95% CI 1.01 to 1.33).
  • Deaths from malignant and non-malignant respiratory diseases: 85 among the 866 asbestos cement workers versus 39 among the 755 controls.
  • Among the asbestos cement workers, seven deaths were due to mesothelioma according to death certificates, and another three were found on histopathological review of tissue from respiratory cancers.
  • The excess mortality among asbestos cement workers appeared confined to 20-40 years from first exposure (HR 1.27, 95% CI 0.99 to 1.62). For 40 years or more since first exposure, the HR was 1.14 (95% CI 0.86 to 1.51), which the authors described as far from significant.
  • Internal analysis, workers employed at least five years, all causes, adjusted for smoking: HR 1.35 (95% CI 0.93 to 1.97) for a cumulative dose of 10 or more f-y/ml at age 40, compared with under 4 f-y/ml. None of the dose-group point estimates were significantly increased.
  • In the internal analysis, tests comparing model scores gave P = 0.057 with dose as categories and P = 0.025 with dose coded by group median. The authors stated that the hypothesis of a trend cannot be rejected.
  • Point estimates of the dose effect were higher for deaths from respiratory diseases only than for all causes. The authors interpreted this as indicating a causal relation with asbestos exposure.
  • Kaplan-Meier median age at death among the 331 workers with at least five years of employment was 75.1 (95% CI 70.0 to 77.4) in the high exposure group and 78.8 (95% CI 71.5 to 80.8) in the low exposure group.
  • In the internal analysis, being a smoker or former smoker was estimated to lower median age at death by 2.7 years (Kaplan-Meier) and by 3.4 years (Cox regression).
• The authors' conclusion: The authors concluded that even a moderate asbestos exposure may shorten the median duration of life in an exposed population. They estimated that the effect of ever being an asbestos cement worker was less than that of ever being a smoker, but the effect of high exposure was similar.
• Limitations the authors state:
  • Smoking habits were known for only 40% of the control workers.
  • Smoking was adjusted only as smoker versus non-smoker, not by quantity of tobacco.
  • Assigning missing smoking information arbitrarily likely led to some underestimation of the smoking effect in the comparison with controls.
  • Exposure assessment had three difficulties: incomplete work histories, conversion between particle and fibre counts, and no dust measurements for 1907-55.
  • The authors did not adjust for present fibre counting methods likely giving about 30%-50% higher concentrations than counts made before 1978.
  • Confidence intervals in the internal analysis were wide and do not permit firm conclusions.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Cumulative Exposure, Hazard Ratio, confidence interval, Habit, Asbestos Exposure.

Related studies

• Lung function predicts survival in a cohort of asbestos cement workers — H. Moshammer, M. Neuberger (2009)
• Mortality and cancer morbidity in cohorts of asbestos cement workers and referents — M. Albin, K. Jakobsson, et al. (1990)
• Regarding "absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: extended follow-up of a cohort", by Murray Finkelstein, American Journal of Industrial Medicine 2010 — R.M. Ross (2011)
• Mortality in a cohort of cement workers in a plant of Central Italy — F. Giordano, V. Dell'orco, et al. (2012)
• Absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: Extended follow-up of a cohort — M.M. Finkelstein (2010)
• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)

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