Vitamin A and cancer prevention I: observations in workers previously exposed to asbestos at Wittenoom, Western Australia

Our plain-English summary of Vitamin A and cancer prevention I: observations in workers previously exposed to asbestos at Wittenoom, Western Australia, by A.W. Musk, N.H. de Klerk, G.L. Ambrosini, et al (International Journal of Cancer, 1998).

The study

• Authors: A.W. Musk, N.H. de Klerk, G.L. Ambrosini, J.L. Eccles, J. Hansen, N.J. Olsen, V.L. Watts, H.G. Lund, S.C. Pang, J. Beilby, M.S. Hobbs
• Journal: International Journal of Cancer
• Published: 1998;75(3):355-61
• Cited by: 58 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Our aim was to describe a vitamin A-based cancer prevention program for former asbestos workers and to check for possible harmful effects by comparing rates of disease and death in study subjects with subjects who chose not to join. All subjects had been occupationally exposed to crocidolite at Wittenoom Gorge between 1943 and 1966; 1,677 subjects indicated interest in the program and 1,203 joined between June 1990 and May 1995. Comparison subjects consisted of 996 former workers known to be alive in Western Australia in 1990 who did not join the program. Program subjects were provided with annual supplies of vitamin A (either synthetic beta-carotene or retinol), help in quitting smoking and dietary advice. The comparison group received only mail contact. Both groups were followed up to December 1994 for vital status and cancer information, and rates of cancer and death from various causes were compared. Mortality in both groups was higher than expected (standardised mortality ratio 1.23 in program subjects and 1.67 in comparison subjects). After adjustment for age, smoking and asbestos exposure, the relative rates in participants compared with non-participants was below I for all examined cancers and causes of death. For mesothelioma and lung cancer, group differences increased with time from entry, whereas other differences dissipated with time. No significant side effects were reported. In conclusion, program participants had significantly lower mortality than non-participants, but the rates of the 2 groups converged with time.

In plain English

This study described a cancer prevention program for people who had worked with crocidolite (blue asbestos) at Wittenoom Gorge, Western Australia, between 1943 and 1966, and checked whether participants came to harm. Program members (1,203) received daily vitamin A as either beta-carotene or retinol, plus help to quit smoking and dietary advice. Up to December 1994, they were compared with 996 former workers living in Western Australia who did not join. The groups differed: participants had heavier asbestos exposure and more ex-smokers. After adjustment, deaths from all causes were lower among participants (relative rate 0.64, 95% confidence interval 0.47–0.88), but the rates drew closer over time and were about equal after about 4.5 years. Malignant mesothelioma (16 cases in each group; relative rate 0.77, 0.38–1.55) and lung cancer (12 versus 30 cases; 0.67, 0.33–1.37) were lower among participants, but not statistically significantly. Reported symptoms were mainly minor skin complaints. Forty-five people stopped retinol because of abnormal liver tests. The authors found no evidence of harm and concluded that similar programs could be used elsewhere, with synthetic beta-carotene replaced.

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: Observational comparison of people who joined a vitamin A cancer prevention program with eligible former workers who did not join, analysed with time-dependent Cox regression. Within the program, people who could attend the clinic were randomly allocated to beta-carotene or retinol.
• Who was studied: Former workers of the Wittenoom crocidolite industry: 1,203 who joined the program between June 1990 and May 1995, and 996 who did not join but were known to be living in Western Australia. Follow-up ran to December 31, 1994. About 92% of program members and 91% of comparison subjects were male.
• Exposure: Past work exposure to crocidolite at Wittenoom Gorge between 1943 and 1966. The program gave daily vitamin A (30 mg beta-carotene or 25,000 IU retinol), help to stop smoking and dietary advice.
• Main results:
  • Compared with the general Western Australian population, the standardised mortality ratio was 1.23 (95% CI 0.97–1.57) in the program group and 1.67 (95% CI 1.42–1.99) in the comparison group.
  • Over the whole study period, deaths from all causes in the program group relative to the comparison group had a relative rate of 0.64 (95% CI 0.47–0.88), after adjustment for age, sex, smoking and asbestos exposure.
  • The all-cause mortality difference between the groups narrowed with time on the program, with rates approximately equal after 4.5 years.
  • There were 16 malignant mesothelioma cases and 12 lung cancer cases in the program group. The comparison group had 16 mesothelioma cases and 30 lung cancer cases.
  • The relative incidence rate of mesothelioma for the program group compared with the comparison group was 0.77 (95% CI 0.38–1.55). There was a widening difference with time on the program, but this was not statistically significant.
  • The relative rate of lung cancer for the program group compared with the comparison group was 0.67 (95% CI 0.33–1.37).
  • Program subjects had similar reductions in deaths from other cancers, ischaemic heart disease and all other causes, but these rates in the two groups tended to converge with time.
  • Among program subjects, 67 people reported 218 symptoms, mainly minor skin complaints. Separately, 45 subjects were taken off retinol because of abnormal liver function tests but stayed in the program.
  • Program subjects were younger and had heavier asbestos exposure than comparison subjects.
• The authors' conclusion: The authors stated that the comparisons gave no evidence of damaging effects to participants. They concluded that similar intervention and surveillance programs could be used elsewhere, with the now discredited synthetic beta-carotene replaced.
• Limitations the authors state:
  • Because the study was observational, the effects of vitamin A cannot be separated from other parts of the program or from self-selection bias.
  • The program and comparison groups differed, with more ex-smokers and heavier asbestos exposure in the program group.
  • The early difference in lung cancer rates could be explained by selection or volunteer bias.
  • Smoking information came only from the 1979 survey, about 11 years before the program began.
  • There were comparatively small numbers of mesothelioma and lung cancer cases.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite, Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Wittenoom, Crocidolite, Asbestos Exposure, Mesothelioma, Lung Cancer.

Related studies

• Vitamin A and cancer prevention II: comparison of the effects of retinol and beta-carotene — N.H. de Klerk, A.W. Musk, et al. (1998)
• Plasma retinol, carotene and vitamin E concentrations and lung function in a crocidolite-exposed cohort from Wittenoom, Western Australia: a cohort study — H.S. Alfonso, L. Fritschi, et al. (2005)
• Retinol supplementation and mesothelioma incidence in workers earlier exposed to blue asbestos (Crocidolite) at Wittenoom, Western Australia — H.S. Alfonso, A. Reid, et al. (2010)
• Plasma vitamin concentrations and incidence of mesothelioma and lung cancer in individuals exposed to crocidolite at Wittenoom, Western Australia — H.S. Alfonso, L. Fritschi, et al. (2006)
• Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia — G. Berry, N.H. de Klerk, et al. (2004)
• Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up — G. Berry, A. Reid, et al. (2012)

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