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Long-term follow-up study of mortality and the incidence of cancer in a cohort of workers at a primary aluminum smelter in Sweden
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
2008 (English)In: Scandinavian Journal of Work, Environment and Health, ISSN 0355-3140, Vol. 34, no 6, 463-470 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: Previous studies on mortality and the incidence of cancer among workers at primary aluminum smelters have produced conclusive results indicating an elevated risk of bladder cancer. An increased risk of lung cancer has also been reported several times. The objective of this study was to examine mortality and the incidence of cancer at a Swedish aluminum smelter when different neighboring reference populations were used to evaluate any relationships to the length of employment. METHODS: A historical cohort--comprised of 2264 male nonoffice workers employed from 1942 on and tracked up to the year 2000--was examined. With the use of three reference populations for mortality and four for cancer incidence, standardized mortality and incidence ratios were calculated, together with hazard ratios derived from Cox regression models. RESULTS: This study showed an excess risk of mortality due to chronic obstructive lung disease, mental disorders, and diseases of the digestive system among the short-term workers. An elevated risk of cancer was found for the lungs, central nervous system, and esophagus. The highest lung cancer risk was observed for the workers employed for > or = 10 years in the factory when they were compared with the reference group from northern Sweden (standardized incidence ratio 1.99, 95% confidence ratio 1.21-3.07). CONCLUSIONS: The results support previous studies that demonstrated an excess risk of lung cancer, but, in contrast to the results of most studies, cancer of the central nervous system was also elevated. This study did not, however, verify an association between this type of exposure and cancer of the urinary organs.

Place, publisher, year, edition, pages
2008. Vol. 34, no 6, 463-470 p.
National Category
Cancer and Oncology Environmental Health and Occupational Health
URN: urn:nbn:se:umu:diva-24844DOI: 10.5271/sjweh.1293PubMedID: 19137208OAI: diva2:227853
Available from: 2009-07-20 Created: 2009-07-20 Last updated: 2013-10-25Bibliographically approved
In thesis
1. Strategies for assessing health risks from two occupational cohorts within the domain of northern Sweden
Open this publication in new window or tab >>Strategies for assessing health risks from two occupational cohorts within the domain of northern Sweden
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Strategier vid utvärdering av hälsorisker baserade på två arbetarekohorter från norra Sverige
Abstract [en]

Background Studies based on a cohort design requires access to both subject-specific and period-specific information. In order to conduct an occupational cohort study, access to exposure information and the possibility and permission to link information on outcomes from other registers are generally necessary. The analysis phase is also aggravated by its added complexity because of the longitudinal dimension of the cohort’s data.This thesis aims at increasing the knowledge on hazards from work on fatalities and cancer within the domain of cohort studies on miners and metal refiners and to study the complexity of the analysis by discussing and suggesting analytical strategies.

Methods The study population for this thesis consisted of a cohort of 2264 blue-collar aluminium smelter workers (paper I) and a cohort of 13000 blue-collar iron-ore miners (papers II-IV), both followed for over 50 years. The outcomes were collected from the Swedish Cause of Death Register and the Swedish Cancer Register. The primary methods of analysis were either Standardized Morbidity Ratios (SMR) or internal comparisons based on Cox or Poisson regression modeling. In paper IV, a g-estimation based on an accelerated failure-time model was performed to estimate the survival ratio.

Results The results from paper I suggested that working as a blue-collar worker metal refiner was associated with increased rates of incidental lung cancer. Elevated rates among short term workers were observed for several outcomes. Paper I also showed that the choice of reference population when calculating SMR could influence the conclusions of the results. In paper II, several outcomes were elevated among the miners compared to the reference population from northern Sweden. However, no outcome except lung cancer was associated with cumulative employment time. The most recurrent pattern of the results was the negative association between cumulative employment time underground and several outcomes. The results from paper III showed that cumulative employment time working outdoors was associated with increased rates of cerebrovascular disease mortality. However, employment with heavy physical workloads did not explain the previously observed decreasing rates in the selected groups of outcomes. The adjustment for the healthy worker survivor effect by g-estimation in paper IV suggested that exposure from respirable dust was associated with elevated mortality risks that could not be observed with standard analytical methods.

Conclusion Our studies found several rates from the cohorts that were elevated compared to external refererence populations but also that long term employments generally were associated with decreasing rates. Furthermore, incidental lung cancer rates was found elevated for the metal refiners. Among the miners, mortality rates of cerebrovascular diseases depended on if work was performed outdoor (higher rates) or underground (lower rates). Methodologically, this thesis has discussed different analytical strategies for handling confounding in occupational cohort studies. Paper IV showed that the healthy worker survivor effect could be adjusted for by performing g-estimation.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2013. 69 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1605
Cohort, mortality, incidence, risk, rate, cancer, cerebrovascular diseases, exposure, occupational, mining, industry, worker, Poisson regression, Cox regression, SMR, causal inference, G-estimation
National Category
Environmental Health and Occupational Health
Research subject
Occupational and Environmental Medicine; Epidemiology
urn:nbn:se:umu:diva-81764 (URN)978-91-7459-742-4 (ISBN)
Public defence
2013-11-15, Tripple helix, Samverkanshuset, Umeå Universitet, Umeå, 13:00 (Swedish)
Available from: 2013-10-25 Created: 2013-10-21 Last updated: 2013-10-25Bibliographically approved

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