Cardiovascular disease mortality among British asbestos workers (1971-2005)

Our plain-English summary of Cardiovascular disease mortality among British asbestos workers (1971-2005), by A.H. Harding, A. Darnton, J. Osman (Occupational and Environmental Medicine, 2012).

The study

• Authors: A.H. Harding, A. Darnton, J. Osman
• Journal: Occupational and Environmental Medicine
• Published: 2012;69(6):417-21
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Asbestos is an inflammatory agent, and there is evidence that inflammatory processes are involved in the development of cardiovascular disease. Whether asbestos is a risk factor for cardiovascular disease has not been established. The objective of this study was to investigate cardiovascular disease mortality in a large cohort of workers occupationally exposed to asbestos.

Methods: Cardiovascular disease mortality in a cohort of 98,912 asbestos workers, with median follow-up of 19 years, was analysed. Unadjusted and smoking-adjusted standardised mortality ratios (SMRs) were calculated. The association between indicators of asbestos exposure and mortality was analysed with Poisson regression models, for deaths occurring during the period 1971-2005.

Results: Altogether 15,557 deaths from all causes, 1053 deaths from cerebrovascular disease and 4185 deaths from ischaemic heart disease (IHD) occurred during follow-up. There was statistically significant excess mortality from cerebrovascular disease (SMR: men 1.63, women 2.04) and IHD (SMR: men 1.39, women 1.89). Job and birth cohort were associated with the risk of cerebrovascular and IHD mortality in the Poisson regression model including sex, age, smoking status, job, cohort and duration of exposure. For IHD only, duration of exposure was also statistically significant in this model.

Conclusions: Cerebrovascular and IHD mortality was significantly higher among these asbestos workers than in the general population and within the cohort mortality was associated with indicators of asbestos exposure. These findings provide some evidence that occupational exposure to asbestos was associated with cardiovascular disease mortality in this group of workers.

In plain English

This study followed 98,912 British asbestos workers (94,403 men and 4509 women) under medical surveillance in the Asbestos Workers Survey. Deaths were followed from 1971 to 2005 (median follow-up 19.3 years). The authors compared cerebrovascular and ischaemic heart disease (IHD) deaths with Great Britain rates, unadjusted and adjusted for smoking. There were 1053 cerebrovascular and 4185 IHD deaths. Unadjusted standardised mortality ratios for cerebrovascular disease were 1.63 (95% CI 1.52 to 1.73) for men and 2.04 (1.64 to 2.51) for women. For IHD they were 1.39 (1.35 to 1.43) for men and 1.89 (1.62 to 2.19) for women. Most smoking-adjusted ratios stayed significantly above 1, except IHD among male never-smokers and both diseases among female former smokers. Within the cohort, risk differed by job type and birth year. IHD risk rose slightly with longer exposure, mainly among never- and former smokers. The authors concluded the findings provide some evidence of an association between occupational asbestos exposure and cardiovascular disease mortality. They noted the lack of individual exposure data, including intensity and asbestos type, and that occupational class may partly explain the excess.

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 (mortality follow-up), using standardised mortality ratios with and without smoking adjustment, and Poisson regression within the cohort
• Who was studied: 98,912 British asbestos workers (94,403 men, 4509 women) taking part in the Asbestos Workers Survey, established in 1971 for workers under medical surveillance required by asbestos regulations. Deaths were followed to the end of 2005, with a median follow-up of 19.3 years. Mean age at first medical exam was 35 years. Most men were in asbestos removal and most women were in manufacturing.
• Exposure: Occupational asbestos exposure, represented by proxy indicators. These were main job type (manufacturing, removal, 'other exposed', insulation), year of birth, and self-reported duration of exposure. The article had no information on exposure intensity or on the type of asbestos.
• Main results:
  • During follow-up the cohort had 15,557 deaths from all causes, 1053 from cerebrovascular disease and 4185 from ischaemic heart disease.
  • Compared with the Great Britain population, the cohort's all-cause SMR was 1.42 (95% CI 1.39 to 1.44).
  • Unadjusted SMRs showed statistically significant excesses in both sexes. For men, cerebrovascular disease was 1.63 (95% CI 1.52 to 1.73) and IHD was 1.39 (95% CI 1.35 to 1.43). For women, cerebrovascular disease was 2.04 (95% CI 1.64 to 2.51) and IHD was 1.89 (95% CI 1.62 to 2.19).
  • Overall smoking-adjusted SMRs were as follows. Among men, cerebrovascular disease was 1.51 (1.42 to 1.61) and IHD was 1.28 (1.24 to 1.32). Among women, cerebrovascular disease was 1.86 (1.49 to 2.28) and IHD was 1.61 (1.38 to 1.87). All smoking-adjusted SMRs stayed significantly above 1 except IHD among male never-smokers (1.04, 0.94 to 1.15) and both diseases among female former smokers.
  • Compared with manufacturing workers, removal workers had a lower risk of death from cerebrovascular disease (RR 0.74, 95% CI 0.60 to 0.90) and from IHD (RR 0.72, 95% CI 0.65 to 0.79). 'Other exposed' workers had a lower risk of IHD only (RR 0.86, 95% CI 0.79 to 0.94). Insulation workers had risks similar to manufacturing workers.
  • Mortality was lower in later birth cohorts. For IHD, mortality rose slightly with longer duration of exposure: those exposed 40 or more years had RR 1.25 (95% CI 1.10 to 1.42) compared with those exposed less than 10 years. For cerebrovascular disease the corresponding RR was 1.22 (0.93 to 1.62).
  • The rise in IHD risk with duration of exposure was mainly among never- and former smokers. Compared with under 10 years of exposure, 40 or more years was linked to 54% higher IHD risk among former smokers, 75% higher among never-smokers, and only 6% higher among current smokers. These interactions were not significant for cerebrovascular disease.
• The authors' conclusion: The authors concluded that the findings provide some evidence of an association between occupational exposure to asbestos and cardiovascular disease mortality in these workers.
• Limitations the authors state:
  • There was no information on individual asbestos exposure, so proxy measures had to be used.
  • Exposure may have been intermittent, and there was no information on exposure intensity or asbestos type.
  • Job categories did not account for differences between individual tasks within each category.
  • The excess mortality remaining after smoking adjustment may be partly due to occupational class rather than asbestos.
  • The lower risk in later birth cohorts may reflect the general fall in cardiovascular deaths in Britain during the study period.
  • Among current smokers, the effect of smoking may have masked any effect of asbestos on cardiovascular risk.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Occupational Exposure.

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