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Reduced mortality rates in a cohort of long-term underground iron-ore miners
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 Radiation Sciences, Oncology.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine. (Arcum)
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2013 (English)In: American Journal of Industrial Medicine, ISSN 0271-3586, E-ISSN 1097-0274, Vol. 56, no 5, 531-540 p.Article in journal, Editorial material (Refereed) Published
Abstract [en]

Background Historically, working in iron-ore mines has been associated with an increased risk of lung cancer and silicosis. However, studies on other causes of mortality are inconsistent and in the case of cancer incidence, sparse. The aim of this study was to examine the association between iron-ore mining, mortality and cancer incidence.

Methods A 54-year cohort study on iron-ore miners from mines in northern Sweden was carried out comprising 13,000 workers. Standardized rate ratios were calculated comparing the disease frequency, mortality, and cancer incidence with that of the general population of northern Sweden. Poisson regression was used to evaluate the association between the durations of employment and underground work, and outcome.

Results Underground mining was associated with a significant decrease in adjusted mortality rate ratios for cerebrovascular and digestive system diseases, and stroke. For several outcomes, elevated standardized rate ratios were observed among blue-collar workers relative to the reference population. However, only the incidence of lung cancer increased with employment time underground (P<0.001).

Conclusions Long-term iron-ore mining underground was associated with lower rates regarding several health outcomes. This is possibly explained by factors related to actual job activities, environmental exposure, or the selection of healthier workers for long-term underground employment.

Am. J. Ind. Med. 56:531540, 2013. (c) 2013 Wiley Periodicals, Inc.

Place, publisher, year, edition, pages
2013. Vol. 56, no 5, 531-540 p.
Keyword [en]
mining, occupational disease, occupational exposure, cancer incidence, mortality
National Category
Environmental Health and Occupational Health
URN: urn:nbn:se:umu:diva-71076DOI: 10.1002/ajim.22168ISI: 000317684400005OAI: diva2:629652
Available from: 2013-06-17 Created: 2013-05-20 Last updated: 2016-08-17Bibliographically 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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Björ, OveJonsson, HåkanDamber, LenaWahlström, JensNilsson, Tohr
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