Retinol supplementation and mesothelioma incidence in workers earlier exposed to blue asbestos (Crocidolite) at Wittenoom, Western Australia

Our plain-English summary of Retinol supplementation and mesothelioma incidence in workers earlier exposed to blue asbestos (Crocidolite) at Wittenoom, Western Australia, by H.S. Alfonso, A. Reid, N.H. de Klerk, et al (European Journal of Cancer Prevention, 2010).

The study

• Authors: H.S. Alfonso, A. Reid, N.H. de Klerk, N. Olsen, R. Mina, G.L. Ambrosini, J. Beilby, G. Berry, B.A. Musk
• Journal: European Journal of Cancer Prevention
• Published: 2010;19(5):355-9
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Owing to the high rates of malignant mesothelioma in workers exposed to crocidolite earlier at Wittenoom and evidence of protection against cancer by vitamin A, a population-based cancer prevention programme providing retinol supplements (25 000 IU/day) was commenced in 1990. The former workers at Wittenoom known to be alive and living in Western Australia in June 1990 constitute the study population. The participants were classified into two groups: those who received supplemental retinol (intervention group) and those who received none (comparison group). The relative rate of mesothelioma for those receiving retinol was estimated using Cox regression, adjusting for cumulative asbestos exposure and age at first exposure to asbestos. Nine hundred and twenty-eight former Wittenoom workers received retinol at some stage of the programme, whereas 1471 workers never received retinol (comparison group). Those who received retinol were younger, had a greater exposure to asbestos and smoked less than the comparison group. There were 65 cases of mesothelioma in the retinol group and 88 in the comparison group. After adjustment, the hazard ratio was 0.99 (95% confidence interval=0.70-1.41). This result did not alter when the participants who received only retinol once or those who received beta-carotene earlier were excluded from the analysis. In conclusion, this study provides little support for possible preventive effects of retinol against mesothelioma in workers exposed to blue asbestos.

In plain English

This study followed former workers exposed to crocidolite (blue asbestos) at Wittenoom, Western Australia, who were alive and living in the state in June 1990. That year a prevention programme began offering retinol (vitamin A), 25 000 IU a day. Participants were first randomly allocated to retinol or beta-carotene, but from 1997 all received retinol. This analysis compared 928 workers who received retinol at some stage with 1471 who never did, a comparison that was not randomized. The retinol group had higher asbestos exposure and fewer smokers. Workers were followed until mesothelioma diagnosis, death, or October 2007. There were 65 mesothelioma cases (pleural and peritoneal combined) in the retinol group and 88 in the comparison group. After adjusting for cumulative asbestos exposure and age, there was no significant difference (hazard ratio 0.99, 95% confidence interval 0.70 to 1.41). Excluding people with only one visit, or who started on beta-carotene, gave similar results. The authors concluded that retinol was not associated with a lower incidence of mesothelioma. They noted that self-selection into the programme may have biased the results.

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: Analysis of a population-based cancer prevention (vitamin A) programme. Programme participants were first randomly allocated to retinol or beta-carotene, and from September 1997 all received retinol. This analysis compared workers who ever received retinol with workers who never did, which was not a randomized comparison. Cox regression was used, with retinol treated as a time-dependent variable.
• Who was studied: Former workers at Wittenoom, Western Australia, known to be alive and living in Western Australia in June 1990. In total 2399 people: 928 who received retinol and 1471 who never did. They were followed from 15 June 1990 until mesothelioma diagnosis or death, or were censored on 15 October 2007.
• Exposure: Earlier occupational exposure to crocidolite (blue asbestos) at Wittenoom, measured as cumulative exposure in fibres/ml year. The intervention studied was supplemental retinol at 25 000 IU/day.
• Main results:
  • Workers who received retinol had higher cumulative asbestos exposure than those who did not: 6.35 vs 4.25 fibre/ml year according to the text. Table 1 gives medians of 6.38 vs 4.32.
  • The retinol group had a median of 193 days working with asbestos, compared with 121 days in the comparison group.
  • Smokers made up 31% of the comparison group and 23% of the retinol group.
  • Participants took retinol supplements for a median of 8.6 years (interquartile range 3.3 to 11.7 years).
  • There were 88 mesothelioma cases in the comparison group (n = 1471) and 65 in the retinol group (n = 928).
  • Crude (unadjusted) mesothelioma rates were lower in the retinol group during the first 3 years of follow-up, and lower in the comparison group after that.
  • After adjusting for cumulative asbestos exposure and age at entry, the relative risk (hazard ratio) of mesothelioma for the retinol group compared with the comparison group was 0.99 (95% CI 0.70 to 1.41). The authors described this as no significant difference.
  • Results were similar in the sensitivity analyses. Excluding 91 participants with just one visit gave a hazard ratio of 1.04 (95% CI 0.74 to 1.48). Excluding 610 participants who started with beta-carotene gave 1.10 (95% CI 0.73 to 1.67).
  • Adjusted annual mesothelioma rates per 1000 person-years were 4.05 (95% CI 3.26 to 5.04) in the comparison group and 4.94 (95% CI 3.80 to 6.43) in the retinol group. The incidence rate ratio was 1.26 (95% CI 0.91 to 1.74).
• The authors' conclusion: The authors concluded that, after more than 15 years of follow-up, retinol supplementation in these former Wittenoom workers was not associated with a lower incidence of malignant mesothelioma. They stated that the study provides little support for a preventive effect of retinol, and that the results do not justify further use of synthetic retinol supplements for attempts at cancer prevention.
• Limitations the authors state:
  • Participants chose for themselves whether to join the programme. The authors said this self-selection may have introduced bias in either direction: healthier people joining, or people with health concerns joining. They added that other unrecognized selection factors may have been operating.
  • The authors suggested that people who developed mesothelioma may not have responded to the supplements, possibly through increased retinol excretion in urine. They could not test this because urinary retinol excretion was not measured.

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, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Crocidolite, Wittenoom, Malignant Mesothelioma, Asbestos Exposure, Hazard Ratio, confidence interval.

Related studies

• 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)
• 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)
• Cancer incidence among women and girls environmentally and occupationally exposed to blue asbestos at Wittenoom, Western Australia — A. Reid, J. Heyworth, et al. (2008)
• Vitamin A and cancer prevention I: observations in workers previously exposed to asbestos at Wittenoom, Western Australia — A.W. Musk, N.H. de Klerk, et al. (1998)
• 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)
• 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)

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