Analysis of mortality in chrysotile asbestos miners in China

Our plain-English summary of Analysis of mortality in chrysotile asbestos miners in China, by L. Du, X. Wang, M. Wang, et al (Journal of Huazhong University of Science and Technology. Medical Sciences = Hua Zhong Ke Ji Da Xue Xue Bao. Yi Xue Ying de Wen Ban = Huazhong Keji Daxue Xuebao. Yixue Yingdewen Ban, 2012).

The study

• Authors: L. Du, X. Wang, M. Wang, Y. Lan
• Journal: Journal of Huazhong University of Science and Technology. Medical Sciences = Hua Zhong Ke Ji Da Xue Xue Bao. Yi Xue Ying de Wen Ban = Huazhong Keji Daxue Xuebao. Yixue Yingdewen Ban
• Published: 2012;32(1):135-140
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In order to investigate the mortality of a cohort of chrysotile asbestos miners in China and evaluate its association with exposure to chrysotile, a fixed cohort of 1932 workers in chrysotile asbestos mine was established in 1981 and followed till June 1, 2010. Information on vital status, cause of death and smoking habits was collected. The workers were divided into two groups according to their exposure status. The exposed group was composed of frontline workers who worked directly on mining or processing asbestos products. The control group consisted of those who were not directly exposed to asbestos in their work. Standardized mortality ratio (SMR) was calculated according to Chinese national death rates. Cox proportional hazards model was applied to estimate the adjusted relative risks of deaths from major causes in exposed and control groups. The results of this study showed that main causes of mortality were malignant neoplasm, cardiovascular disease, cerebrovascular disease and respiratory disease for chrysotile miners. The mortality rate was 939.20 per 100 000 person-years for workers. The SMR for all causes of death was 1.46 in the cohort. Statistically significant mortality excesses were found for lung cancer (SMR=1.51), pulmonary heart disease (SMR=2.70), respiratory disease (SMR=1.93), asbestosis (SMR=9.62), and accident (SMR=1.59). The mortalities from malignant neoplasm, lung cancer, cerebrovascular disease and digestive disease in the exposed group were significantly higher than those in the control group. The findings indicate that chrysotile exposure is a risk factor for lung cancer, respiratory disease, cerebrovascular disease and digestive disease.

In plain English

The authors followed 1932 workers at a chrysotile asbestos mine in Qinghai province, China, from 1981 to June 2010. They compared 1257 frontline mining and processing workers with 675 management and service workers. Work-area dust levels in 2009 ranged from 4.33 to 196.67 mg/m3, and fiber data were unavailable. There were 473 deaths. Whole-cohort all-cause mortality was 46% higher than national rates (SMR 1.46, 95% CI 1.33 to 1.60). The lung cancer SMR was 2.50 (95% CI 1.85 to 3.24) in the exposed group and 1.01 (0.52 to 1.65) in controls. Compared with controls, exposed workers had higher adjusted death risks for all causes (RR 1.91, 95% CI 1.54 to 2.37), lung cancer (2.57, 1.35 to 4.88), liver cancer (5.04, 1.14 to 22.37), cerebrovascular disease (1.75, 1.00 to 3.08) and digestive disease (5.95, 1.37 to 25.88). The increase for nonmalignant respiratory disease was not statistically significant. No worker had mesothelioma. The authors concluded that chrysotile exposure was a risk factor for lung cancer, respiratory disease, cerebrovascular disease and digestive disease. They noted possible exposure misclassification, few pathological diagnoses and the healthy worker effect.

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 mortality study using two comparisons: workers directly exposed to asbestos against an internal control group of mine workers not directly exposed, and the whole cohort against Chinese national death rates (standardized mortality ratios). Relative risks were estimated with Cox proportional hazards models.
• Who was studied: 1932 workers at the Qinghai chrysotile asbestos mine, China. All were on the mine's register and had worked there at least one year between January 1, 1981 and December 31, 1988. They were followed to June 1, 2010, for 50 362 person-years. The exposed group had 1257 workers and the control group had 675.
• Exposure: Chrysotile asbestos mining and processing. The exposed group was frontline workers: mining, blasters, mechanic, maintenance, transport workers and lab technicians. Dust concentrations measured in work areas in 2009 ranged between 4.33 and 196.67 mg/m3. Fiber data were not available.
• Main results:
  • 473 of the 1932 workers (24.5%) died during follow-up. The mortality rate was 939.2 per 100 000 person-years.
  • Whole cohort: deaths from all causes were 46% higher than the national average (SMR 1.46, 95% CI 1.33 to 1.60, from Table 3).
  • All causes: deaths were 75% higher than the national average in the exposed group (SMR 1.75, 95% CI 1.57 to 1.94). The control group was similar to the national average (SMR 0.92, 95% CI 0.76 to 1.10).
  • Lung cancer, exposed group, compared with national rates: SMR 2.50 (95% CI 1.85 to 3.24), based on 50 deaths.
  • Lung cancer, control group, compared with national rates: SMR 1.01 (95% CI 0.52 to 1.65), based on 12 deaths.
  • Exposed group compared with control group (adjusted relative risks): all causes RR 1.91 (95% CI 1.54 to 2.37); malignant neoplasm RR 2.38 (95% CI 1.56 to 3.65).
  • Exposed group compared with control group: lung cancer RR 2.57 (95% CI 1.35 to 4.88), from 50 deaths in the exposed group and 12 in the control group. Liver cancer RR 5.04 (95% CI 1.14 to 22.37), from 16 deaths and 2 deaths.
  • Exposed group compared with control group: cerebrovascular disease RR 1.75 (95% CI 1.00 to 3.08), from 50 deaths in the exposed group and 17 in the control group.
  • Exposed group compared with control group: digestive disease RR 5.95 (95% CI 1.37 to 25.88), from 20 deaths in the exposed group and 2 in the control group.
  • Nonmalignant respiratory disease, exposed group compared with control group: risk was increased but not statistically significant (RR 1.39, 95% CI 0.75 to 2.60).
  • Respiratory disease, whole cohort, compared with national rates: mortality was significantly higher (SMR 1.93, 95% CI 1.46 to 2.46).
  • No worker in the cohort had mesothelioma.
  • Asbestosis cases (cases diagnosed, not deaths): 58 of 1063 exposed men (5.46%) and 4 of 194 exposed women (2.06%). There were no cases in the control group.
  • All workers, smokers compared with non-smokers: lung cancer RR 2.88 (95% CI 0.99 to 8.35). The authors described this association as marginally significant.
• The authors' conclusion: The authors concluded that exposed workers had higher mortality, and that chrysotile exposure was a risk factor for lung cancer, respiratory disease, cerebrovascular disease and digestive disease.
• Limitations the authors state:
  • Grouping workers by exposure status may have misclassified exposure.
  • Possible diagnostic bias: few deaths had pathological diagnoses by biopsy or autopsy.
  • The healthy worker effect.
  • The control group also worked in the mine and may have had some asbestos exposure. The authors gave this as the explanation for the non-significant respiratory disease comparison.

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, Habit, standardized mortality ratio (SMR), Relative Risk, Neoplasm, Lung Cancer.

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