The asbestos-asbestosis exposure-response relationship: a cohort study of the general working population

Our plain-English summary of The asbestos-asbestosis exposure-response relationship: a cohort study of the general working population, by I.B. Iversen, J.M. Vestergaard, J. Ohlander, et al (Scandinavian Journal of Work, Environment & Health, 2024).

The study

• Authors: I.B. Iversen, J.M. Vestergaard, J. Ohlander, S. Peters, E. Bendstrup, J.P.E. Bonde, V. Schlünssen, J.H. Bønløkke, F. Rasmussen, Z.A. Stokholm, M.B. Andersen, H. Kromhout, H.A. Kolstad
• Journal: Scandinavian Journal of Work, Environment & Health
• Published: 2024;50(5):372-379
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: The association between asbestos exposure and asbestosis in high-exposed industrial cohorts is well-known, but there is a lack of knowledge about the exposure-response relationship for asbestosis in a general working population setting. We examined the exposure-response relationship between occupational asbestos exposure and asbestosis in asbestos-exposed workers of the Danish general working population.

Methods: We followed all asbestos-exposed workers from 1979 to 2015 and identified incident cases of asbestosis using the Danish National Patient Register. Individual asbestos exposure was estimated with a quantitative job exposure matrix (SYN-JEM) from 1976 onwards and back-extrapolated to age 16 for those exposed in 1976. Exposure-response relations for cumulative exposure and other exposure metrics were analyzed using a discrete time hazard model and adjusted for potential confounders.

Results: The range of cumulative exposure in the population was 0.001 to 18 fibers per milliliter-year (f/ml-year). We found increasing incidence rate ratios (IRR) of asbestosis with increasing cumulative asbestos exposure with a fully adjusted IRR per 1 f/ml-years of 1.18 [95% confidence interval (CI) 1.15- -1.22]. The IRR was 1.94 (95% CI 1.53-2.47) in the highest compared to the lowest exposure tertile. We similarly observed increasing risk with increasing cumulative exposure in the inception population.

Conclusions: This study found exposure-response relations between cumulative asbestos exposure and incident asbestosis in the Danish general working population with mainly low-level exposed occupations, but there is some uncertainty regarding the exposure levels.

In plain English

This Danish nationwide cohort study examined whether the risk of asbestosis rose with the amount of work-related asbestos exposure in the general working population, including all asbestos-exposed workers in Denmark. The authors followed 1 514 136 workers who had ever held an asbestos-exposed job from 1979 to 2015 and found 1084 new asbestosis diagnoses in the national hospital register. Exposure was estimated from job titles using a job exposure matrix (SYN-JEM). Cumulative exposure ranged from 0.001 to 18 fibers per milliliter-year. After adjustment for factors including age, sex, estimated smoking and other dusts, each 1 f/ml-year was associated with an incidence rate ratio of 1.18 (95% CI 1.15–1.22). The highest exposure third had a ratio of 1.94 (95% CI 1.53–2.47) compared with the lowest. A group born 1956 or later with complete work histories since age 20 showed a similar pattern, but this rested on only 17 cases with wide confidence intervals. No trend was seen for idiopathic pulmonary fibrosis. The authors concluded that asbestosis risk rose with cumulative exposure. They noted that the exposure estimates are uncertain and that misdiagnosis could inflate the risk estimates.

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: Nationwide register-based cohort study (discrete time hazard model) of asbestos-exposed workers in Denmark
• Who was studied: 1 514 136 workers in Denmark born 1900 or later with at least one year in an asbestos-exposed occupation, drawn from the DOC*X cohort and followed 1979–2015 (33 878 817 person-years, 1084 asbestosis cases). The inception population comprised 901 957 workers born 1956 or later with complete work histories since age 20 (17 cases).
• Exposure: Occupational asbestos exposure (fiber type not specified) estimated from 1976 onward with the ISCO-88 version of the SYN-JEM job exposure matrix and back-extrapolated to age 16 for workers exposed in 1976. Metrics were cumulative exposure (0.001–18 f/ml-year), highest attained intensity and duration. Construction, the metal industry and motor vehicle and other mechanics accounted for more than 50% of exposed person-years.
• Main results:
  • Total study population, fully adjusted: IRR of asbestosis 1.18 (95% CI 1.15–1.22) per 1 f/ml-year of cumulative exposure, and 1.94 (95% CI 1.53–2.47) for the highest compared with the lowest cumulative exposure tertile
  • Middle cumulative exposure tertile (0.027–0.14 f/ml-years, 200 cases): IRR 1.14 (0.88–1.48) partially adjusted and 1.11 (0.85–1.44) fully adjusted, compared with the lowest tertile (83 cases). The highest tertile had 801 cases.
  • Highest attained exposure intensity: fully adjusted IRR 1.09 (95% CI 1.08–1.11) per 0.01 f/ml, and 2.35 (95% CI 1.78–3.11) for the highest compared with the lowest tertile
  • Duration of exposure: fully adjusted IRR 1.06 per five years (95% CI 1.04–1.08), and 1.43 (95% CI 1.18–1.75) for the highest compared with the lowest duration tertile
  • In analyses split by sex, risk rose with cumulative exposure for men but not for women; only 20 asbestosis cases occurred among women
  • Inception population (17 cases): fully adjusted IRR 1.17 (95% CI 0.94–1.45) per 0.1 f/ml-years, and 1.25 (0.31–5.07) for the highest compared with the lowest tertile. The authors noted these results were based on few cases and had wide confidence intervals.
  • Idiopathic pulmonary fibrosis (supplementary analysis): no trend for any exposure metric; fully adjusted IRR 0.97 (0.76–1.24) per 1 f/ml-years of cumulative exposure
• The authors' conclusion: The authors concluded that there were exposure–response relations between cumulative asbestos exposure and incident asbestosis in the Danish general working population, which was mostly in low-exposed occupations, but that the exposure levels are somewhat uncertain
• Limitations the authors state:
  • No occupation data before 1976 (an estimated 23% of potentially employed years were missing), likely leading to substantial underestimation of cumulative exposure. Back-extrapolation may also have overestimated duration of exposure.
  • Other interstitial lung diseases may be misclassified as asbestosis more often in high-exposed workers, for example because compensation is available for asbestosis, which could inflate risk estimates
  • Because asbestosis is defined partly by exposure, the most-exposed workers within an occupation are most likely to be diagnosed, so job-matrix averages may not represent the cases and may inflate the exposure–response relationship
  • No information on the diagnostic process for individual cases, and high exposure may have increased the likelihood of hospital referral
  • The ISCO-88 version of SYN-JEM and its use of geometric means produce lower exposure levels; arithmetic means would have given about 60% higher cumulative exposure
  • A possible healthy worker survivor effect (the unemployed or retired were overrepresented in the highest exposure tertile), which would lead to underestimation of the exposure–response relationship

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, Asbestos Exposure, Cumulative Exposure, Incidence, confidence interval.

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