A 37-year observation of mortality in Chinese chrysotile asbestos workers

Our plain-English summary of A 37-year observation of mortality in Chinese chrysotile asbestos workers, by X. Wang, E. Yano, H. Qiu, et al (Thorax, 2012).

The study

• Authors: X. Wang, E. Yano, H. Qiu, I. Yu, M.N. Courtice, L.A. Tse, S. Lin, M. Wang
• Journal: Thorax
• Published: 2012;67(2):106-10
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: This 37-year prospective cohort study was undertaken to provide additional evidence for mortality risks associated with exposure to chrysotile asbestos.

Methods: 577 asbestos workers and 435 control workers in original cohorts were followed from 1972 to 2008, achieving a follow-up rate of 99% and 73%, respectively. Morality rates were determined based on person-years of observation. Cox proportional hazard models were constructed to estimate HRs of cause-specific mortality, while taking into account age, smoking and asbestos exposure level.

Results: There were 259 (45%) deaths identified in the asbestos cohort, and 96 died of all cancers. Lung cancer (n=53) and non-malignant respiratory diseases (n=81) were major cause-specific deaths, in contrast to nine lung cancers and 11 respiratory diseases in the controls. Age and smoking-adjusted HRs for mortality by all causes and all cancers in asbestos workers were 2.05 (95% CI 1.56 to 2.68) and 1.89 (1.25 to 2.87), respectively. The risks for lung cancer and respiratory disease deaths in asbestos workers were over threefold that in the controls (HR 3.31(95% CI 1.60 to 6.87); HR 3.23 (95% CI 1.68 to 6.22), respectively). There was a clear exposure-response trend with asbestos exposure level and lung cancer mortality in both smokers and non-smokers.

Conclusion: Data from this prospective cohort provide strong evidence for increased mortality risks, particularly from lung cancer and non-malignant respiratory diseases, associated with exposure to chrysotile asbestos, while taking into account of the smoking effect.

In plain English

This prospective cohort study followed male workers at a Chinese asbestos factory where, according to factory records, only chrysotile was used. The authors compared 577 asbestos workers with 435 male workers from an electronics factory in the same city, from 1972 to 2008. By the end, 259 asbestos workers (45%) had died, against 76 controls (18%). Among asbestos workers, 53 died of lung cancer, 81 of non-malignant respiratory diseases and 2 of mesothelioma (one pleural, one peritoneal). Adjusted for age and smoking, the hazard ratio for lung cancer death in asbestos workers versus controls was 3.31 (95% CI 1.60 to 6.87), and for non-malignant respiratory disease 3.23 (1.68 to 6.22). Lung cancer risk rose with job-based exposure level, to 6.01 (2.74 to 13.19) in the highest group, a trend the authors saw in both smokers and non-smokers. The study did not find increased gastrointestinal cancer deaths. The authors concluded the excess deaths were most likely attributable to chrysotile. They noted no fibre or personal measurements before 1999 and that 27% of controls were lost to follow-up.

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: Prospective cohort study comparing asbestos factory workers with an unexposed industrial control cohort, followed for 37 years
• Who was studied: 586 male asbestos workers on the roster of an asbestos manufacturing factory in China on 1 January 1972, of whom 577 (99%) were traced. A control cohort of 599 male workers from an electronics equipment factory in the same city had no exposure to asbestos or other industrial dusts, and 435 (73%) of them were traced. Both groups were followed to 31 December 2008.
• Exposure: Chrysotile asbestos in a manufacturing factory. Factory records showed only chrysotile was used, and tested samples showed a very low level of tremolite. Workers were grouped by job: high exposure (raw material and textile sections), medium (maintenance) and low (rubber, cement, administration and other services). Average total exposure was 25 years. 2002 area samples gave median fibre concentrations of 7.2 f/cm3 in raw material, 2.1 in textile and 0.8 in rubber plate.
• Main results:
  • 259 asbestos workers (45%) died during follow-up, compared with 76 control workers (18%).
  • Among asbestos workers there were 53 lung cancer deaths, about a fifth of all deaths in that cohort.
  • 81 asbestos workers (31.3% of deaths) died of non-malignant respiratory diseases; 39 of them had been diagnosed with asbestosis.
  • In the control cohort, 33 workers died of cancer, including 9 lung cancers and 18 gastrointestinal cancers; 11 died of non-malignant respiratory diseases.
  • Two mesothelioma deaths occurred among the asbestos workers, one pleural and one peritoneal. There were none in the controls.
  • 127 asbestos workers (22%) were diagnosed with asbestosis.
  • Age-adjusted mortality from lung cancer was 9.6 times, and from non-malignant respiratory diseases 6.4 times, that in the controls. The rates were 588.50 versus 61.23 lung cancer deaths per 100 000 person-years.
  • Hazard ratios for asbestos workers versus controls, adjusted for smoking and age at entry: all causes 2.05 (95% CI 1.56 to 2.68); all cancers 1.89 (1.25 to 2.87); lung cancer 3.31 (1.60 to 6.87); gastrointestinal cancer 1.14 (0.61 to 2.14); non-malignant respiratory diseases 3.23 (1.68 to 6.22).
  • Gastrointestinal cancer mortality in asbestos workers was not higher than in the controls.
  • Asbestos workers in the high exposure group had a lung cancer death hazard ratio of 6.01 (95% CI 2.74 to 13.19) compared with controls. The p for trend across the three exposure levels was less than 0.001 for lung cancer and for non-malignant respiratory diseases.
  • In the low exposure group, the lung cancer hazard ratio was 1.94 (95% CI 0.84 to 4.46). This confidence interval includes 1.
  • Asbestos workers who smoked had a lung cancer death hazard ratio of 17.35 (95% CI 2.38 to 126.57) compared with non-smoking controls.
  • Non-smoking asbestos workers had a lung cancer hazard ratio of 7.52 (95% CI 0.90 to 62.79) compared with non-smoking controls.
  • The synergy index for smoking combined with asbestos was 1.414 (95% CI 0.734 to 3.987). The authors read this as a more-than-additive joint effect that was not statistically significant.
  • Lung cancer risk increased with exposure level in both smokers and non-smokers.
• The authors' conclusion: The authors concluded that the excess deaths, especially from lung cancer and non-malignant respiratory diseases, were most likely attributable to chrysotile asbestos exposure. Their reasons were that smoking was taken into account and that increased risk was also seen in non-smokers.
• Limitations the authors state:
  • No fibre concentrations or personal samples were available before 1999, so exposure levels were based on job categories.
  • Exposure misclassification remained likely, which the authors said could have led to underestimating the associations.
  • Only about half of the malignant tumours were confirmed by biopsy or autopsy. The rest were diagnosed from CT and clinical course.
  • 27% of control workers were lost to follow-up, which the authors said could have led to overestimating the effect estimates.
  • The small number of lung cancer cases limited statistical power for the smoking and asbestos interaction analysis.
  • Smoking could only be recorded as never versus ever, because smoking amounts were missing or uncertain for some workers.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Cohort Study, Asbestos Exposure, Lung Cancer.

Related studies

• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Cancer mortality in Chinese chrysotile asbestos miners: exposure-response relationships — X. Wang, E. Yano, et al. (2013)
• Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort — S. Lin, X. Wang, et al. (2012)
• 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)
• Cancer mortality among Chinese chrysotile asbestos textile workers — X.R. Wang, I.T. Yu, et al. (2012)

Browse more research in Thorax, or return to medical research.