An Evaluation of Mortality Rates and Their Determinants in a Cohort of Former Asbestos Miners in South Africa

Our plain-English summary of An Evaluation of Mortality Rates and Their Determinants in a Cohort of Former Asbestos Miners in South Africa, by Y. Williams-Mohamed, R. Ehrlich, J. teWaterNaude, et al (American Journal of Industrial Medicine, 2026).

The study

• Authors: Y. Williams-Mohamed, R. Ehrlich, J. teWaterNaude, S. Adams
• Journal: American Journal of Industrial Medicine
• Published: 2026;69(6):446-460
• Read it: PubMed · Publisher · Free full text

Abstract

Background: A causal association between occupational asbestos exposure and lung disease, including pneumoconiosis and mesothelioma, is well established. Elevated mortality among former asbestos miners is expected. However, large-scale South African studies examining all-cause mortality in this population are lacking. We assessed all-cause mortality among former asbestos miners recorded in the Asbestos and Kgalagadi Relief Trusts' Inyosi database.

Methods: All-cause standard mortality ratios (SMRs) and crude mortality rates (CMRs) were calculated for 11,343 ex-miners. Mortality predictors were modeled using Cox regression analysis, and mortality trends were assessed by examining annual all-cause CMRs and SMRs over the 20-year study period.

Results: The cohort's all-cause mortality exceeded that of the general population by 4% (SMR = 1.04; 95% CI: 1.01-1.07), with excess mortality confined to women (SMR = 1.17; 95% CI: 1.09-1.25). Increasing ILO radiographic profusion category strongly predicted mortality, with adjusted hazard ratios (aHRs) ranging from 1.13 (95% CI: 1.05-1.23) to 2.42 (95% CI: 1.58-3.71). Severely reduced lung function was also associated with increased risk, including forced expiratory volume in 1 s and forced vital capacity z-scores below -3.0 (aHR = 1.60; 95% CI: 1.41-1.81 and aHR = 1.26; 95% CI: 1.12-1.42, respectively). Additional predictors included body mass index less than 18.5 kg/m² (aHR = 1.46; 95% CI: 1.36-1.58) and previous smoking (aHR = 1.43; 95% CI: 1.35-1.53). SMRs declined over time.

Conclusion: Radiological and spirometric indicators were key predictors of mortality. These findings support risk stratification and targeted interventions, particularly early management of respiratory complications and smoking cessation, to reduce mortality. The excess female mortality highlights the occupational hazards of aboveground asbestos activities, gender‑specific work practices, and insufficient control measures in this setting. Although standardized mortality was only modestly elevated, interpretation was limited by incomplete data.

© 2026 The Author(s). American Journal of Industrial Medicine published by Wiley Periodicals LLC.

In plain English

This retrospective cohort study followed 11,343 former South African asbestos miners registered with the Asbestos and Kgalagadi Relief Trusts, from 2004 to March 2023. Recorded exposure was mostly crocidolite (43.1%); 33.1% was unspecified. By 2023, 5,106 (45.0%) had died, and 43.7% of deaths occurred before age 55. Deaths were 4% above general-population expectations (SMR 1.04; 95% CI 1.01 to 1.07). The excess was statistically significant only in women (SMR 1.17; 95% CI 1.09 to 1.25), not men (SMR 1.02; 95% CI 0.99 to 1.05). Compared with ILO chest X-ray category 0, adjusted hazard ratios were 1.13 (95% CI 1.05 to 1.23) in category 1 and 2.42 (95% CI 1.58 to 3.71) in category 3. Compared with participants without Trust-defined asbestos-related disease, they were 3.85 (95% CI 2.47 to 6.01) for asbestos-related lung cancer and 6.37 (95% CI 5.43 to 7.47) for mesothelioma. Severely reduced lung function, underweight and past smoking also predicted higher risk. Causes of death were not collected. The authors concluded that key clinical predictors were identified, though incomplete data limited definitive conclusions.

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 study using the Trusts' administrative database. It compared deaths with the general population (standardized mortality ratios) and used Cox regression to find predictors of death.
• Who was studied: 11,343 former asbestos miners in South Africa registered as potential claimants on the Asbestos and Kgalagadi Relief Trusts' Inyosi database, followed from January 1, 2004 to March 21, 2023. Of these, 82.8% were male and the median age at entry was 53.1 years.
• Exposure: Asbestos mining work. Recorded fiber type:
• crocidolite only: 43.1%
• chrysotile only: 20.6%
• amosite only: 2.5%
• mixed: 0.7%
• unspecified: 33.1%

75.8% worked only aboveground, and 67.4% had less than 5 years of exposure.

• Main results:
  • Whole cohort: 136,549 person-years of follow-up, 5,106 deaths (45.0%), crude mortality rate 37.4 per 1000 person-years.
  • Whole cohort compared with the general South African population: 5,106 observed vs 4,902 expected deaths, SMR 1.04 (95% CI 1.01 to 1.07).
  • Women: SMR 1.17 (95% CI 1.09 to 1.25). Men: SMR 1.02 (95% CI 0.99 to 1.05), no significant elevation.
  • Among all deaths in the cohort, 43.7% occurred before age 55.
  • ILO radiographic profusion category, compared with category 0:
• category 1: adjusted hazard ratio 1.13 (95% CI 1.05 to 1.23)
• category 2: 1.23 (95% CI 1.00 to 1.52)
• category 3: 2.42 (95% CI 1.58 to 3.71)
  • Severely reduced lung function (z-score below minus 3.0), compared with normal:
• FEV1: aHR 1.60 (95% CI 1.41 to 1.81)
• FVC: aHR 1.26 (95% CI 1.12 to 1.42)
  • Trust-defined disease categories, compared with those without asbestos-related disease:
• asbestos-related lung cancer (ARD 3): aHR 3.85 (95% CI 2.47 to 6.01)
• mesothelioma (ARD 4): aHR 6.37 (95% CI 5.43 to 7.47)
  • Underweight at baseline (BMI below 18.5) vs normal BMI: aHR 1.46 (95% CI 1.36 to 1.58).
  • Previous smokers vs never smokers: aHR 1.43 (95% CI 1.35 to 1.53).
  • Aboveground-only work vs underground-only work: aHR 1.16 (95% CI 1.07 to 1.25).
  • Crocidolite-only vs chrysotile-only exposure: aHR 1.08 (95% CI 0.99 to 1.16). The difference was not statistically significant.
  • Pleural plaques present vs absent: aHR 0.85 (95% CI 0.79 to 0.91), in the model adjusted for all covariates.
  • No clear exposure-response relationship was seen between length of employment and mortality.
  • By calendar year, SMRs rose from 0.85 in 2004 to 1.29 in 2010, then fell to 1.09 by 2018. They fluctuated in 2019 to 2023.
• The authors' conclusion: The authors concluded that, although incomplete data limited definitive conclusions on mortality, the study identified key clinical predictors of mortality, notably radiologic and spirometric abnormalities. They also attributed the excess female mortality to hazards of aboveground asbestos work, laundering exposure, and insufficient protective measures.
• Limitations the authors state:
  • Cause-of-death data were not available, so deaths could not be attributed to asbestos-related disease.
  • Survivorship bias: miners who died before the Trusts were set up were likely missed, which the authors say probably lowered the SMR.
  • Historical inconsistencies in South African death registration may have led to incomplete mortality reporting.
  • Expected deaths came from national rates adjusted only for age and sex. Other confounders, including socioeconomic status and race, were not accounted for.
  • Follow-up started at database entry, which may not reflect the onset of exposure-related risk and could bias survival estimates.
  • Exposure assessment was limited: employment duration was missing for many participants, and histories were self-reported.
  • The cohort was predominantly crocidolite-exposed, so findings may not generalize to mainly chrysotile-exposed populations.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Pneumoconiosis, Mesothelioma, Hazard Ratio.

Related studies

• The mortality of amphibole miners in South Africa, 1946-80 — G.K. Sluis-Cremer, F.D. Liddell, et al. (1992)
• Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa — G.K. Sluis-Cremer, P.A. Hessel, et al. (1989)
• Trends in mesothelioma mortality rates in South Africa: 1995-2007 — D. Kielkowski, G. Nelson, et al. (2011)
• Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort — S. Lin, X. Wang, et al. (2014)
• Mortality in a Chinese chrysotile miner cohort — X. Wang, S. Lin, et al. (2012)
• Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa — J.L. Botha, L.M. Irwig, et al. (1986)

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