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

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.

Statins Do Not Alter the Incidence of Mesothelioma in Asbestos Exposed Mice or Humans

“…This is consistent with the finding that in humans beta carotene and retinoic acid forms of vitamin A do not affect mesothelioma incidence [11]. We have also investigated the use of aspirin and cyclooxygenase-2 inhibitors (COX-2i), again finding no benefit in either the mouse model or a human cohort [12], [13].…”

“…Our two previous investigations addressed vitamin A and non-steroidal anti-inflammatory drug usage and mesothelioma incidence [9], [11]. In the vitamin A trials in both the Wittenoom cohort and the MexTAg mice, the supplementation level was fixed and controlled, and both trials demonstrated no benefit in vitamin A supplementation, despite a strong rationale for a preventative effect.…”

Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up

“…It was necessary to use both methods as it is impossible to obtain a confirmation of ‘still alive' from official records in Australia. About 2500 of the men responded to a smoking questionnaire first issued in 1979 (de Klerk et al , 1991), and repeated at intervals since, and in a study of retinol supplementation that started in 1990 (Alfonso et al , 2010), so that there is a recent information on the date last known to be alive for many in this group. The rates calculated with Method 1 are under estimates as there will be some deaths occurring before the age of 85, which have not been discovered through death searches.…”

Predicting survival in malignant mesothelioma

“…In addition, the records of the Wittenoom worker and resident cohorts, which were established in 1975 and 1985, respectively, record all employees of the Australian Blue Asbestos Company and all township residents identifiable from available public records, and have allowed identification and complete follow-up of those who have developed MM [23]. A cancer prevention programme for people with previous asbestos exposure has also been conducted in Western Australia since 1990 (with .4,000 participants enrolled at some stage [27][28][29]). This provides details of their past exposures to asbestos and further improves the quality of the information available to the registry committee.…”