Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Strategies for assessing health risks from two occupational cohorts within the domain of northern Sweden
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Strategier vid utvärdering av hälsorisker baserade på två arbetarekohorter från norra Sverige (Swedish)
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.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1605
Keyword [en]
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
Identifiers
URN: urn:nbn:se:umu:diva-81764ISBN: 978-91-7459-742-4 (print)OAI: oai:DiVA.org:umu-81764DiVA: diva2:658575
Public defence
2013-11-15, Tripple helix, Samverkanshuset, Umeå Universitet, Umeå, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2013-10-25 Created: 2013-10-21 Last updated: 2013-10-25Bibliographically approved
List of papers
1. Long-term follow-up study of mortality and the incidence of cancer in a cohort of workers at a primary aluminum smelter in Sweden
Open this publication in new window or tab >>Long-term follow-up study of mortality and the incidence of cancer in a cohort of workers at a primary aluminum smelter in Sweden
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.

National Category
Cancer and Oncology Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-24844 (URN)10.5271/sjweh.1293 (DOI)19137208 (PubMedID)
Available from: 2009-07-20 Created: 2009-07-20 Last updated: 2013-10-25Bibliographically approved
2. Reduced mortality rates in a cohort of long-term underground iron-ore miners
Open this publication in new window or tab >>Reduced mortality rates in a cohort of long-term underground iron-ore miners
Show others...
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.

Keyword
mining, occupational disease, occupational exposure, cancer incidence, mortality
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-71076 (URN)10.1002/ajim.22168 (DOI)000317684400005 ()
Available from: 2013-06-17 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically approved
3. Do physical workload or temperature characteristics in an outdoor workingenvironment explain deviating rates of mortality and incidental cancer? A cohort study based on iron-ore mining.
Open this publication in new window or tab >>Do physical workload or temperature characteristics in an outdoor workingenvironment explain deviating rates of mortality and incidental cancer? A cohort study based on iron-ore mining.
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background A cohort study that examined iron ore mining found negative associations between cumulative working time employed underground and several severe outcomes. In this cohort study, and using the same group of miners, we examined whether heavy physical workload or the temperature characteristics represented by an outdoor working environment could explain these lower rates.

Method This study was based on a Swedish iron ore mining cohort consisting of 13000 workers employed between 1923 and 1998. Exposure was defined as cumulative employment time in heavy physical workload or outdoor work. Poisson regression models were used to generate smoothed estimates of standardized morbidity ratios and adjusted rate ratios, both models by cumulative exposure time. SMRs for different cohort subgroups were used to compare the occurrence of cerebrovascular disease mortality to the reference population.

Results The adjusted rate ratio between employment classified as outdoor work ≥25 years and short term outdoor work was 1.62 (95% CI 1.07–2.42). The subgroup underground work ≥15 years deviated most in occurrence of cerebrovascular disease mortality compared with the reference population: SMR (0.70 (95% CI 0.56–0.85)). No elevated rates were associated with cumulative employment time representing heavy physical workloads.

Conclusion Employment in temperature shifting outdoor environments was associated with elevated rates of cerebrovascular disease mortality. In contrast, work in tempered underground employment was associated with a protecting effect. Based on selected groups of mortalities, physically heavy workloads did not protect for mortality later in life.

Keyword
Poisson regression, occupation, standardized mortality ratio, mortality, cancer incidence, cohort, mining
National Category
Environmental Health and Occupational Health
Research subject
Occupational and Environmental Medicine
Identifiers
urn:nbn:se:umu:diva-81783 (URN)
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2013-10-30Bibliographically approved
4. A comparison between standard methods and structural nested modelling when bias from a healthy worker survivor effect is suspected: an iron-ore mining cohort study
Open this publication in new window or tab >>A comparison between standard methods and structural nested modelling when bias from a healthy worker survivor effect is suspected: an iron-ore mining cohort study
2015 (English)In: Occupational and Environmental Medicine, ISSN 1351-0711, E-ISSN 1470-7926, Vol. 72, no 7, 536-542 p.Article in journal (Refereed) Published
Abstract [en]

Objectives Iron-ore miners are exposed to extremely dusty and physically arduous work environments. The demanding activities of mining select healthier workers with longer work histories (ie, the Healthy Worker Survivor Effect (HWSE)), and could have a reversing effect on the exposure-response association. The objective of this study was to evaluate an iron-ore mining cohort to determine whether the effect of respirable dust was confounded by the presence of an HWSE. Methods When an HWSE exists, standard modelling methods, such as Cox regression analysis, produce biased results. We compared results from g-estimation of accelerated failure-time modelling adjusted for HWSE with corresponding unadjusted Cox regression modelling results. Results For all-cause mortality when adjusting for the HWSE, cumulative exposure from respirable dust was associated with a 6% decrease of life expectancy if exposed >= 15 years, compared with never being exposed. Respirable dust continued to be associated with mortality after censoring outcomes known to be associated with dust when adjusting for the HWSE. In contrast, results based on Cox regression analysis did not support that an association was present. Conclusions The adjustment for the HWSE made a difference when estimating the risk of mortality from respirable dust. The results of this study, therefore, support the recommendation that standard methods of analysis should be complemented with structural modelling analysis techniques, such as g-estimation of accelerated failure-time modelling, to adjust for the HWSE.

Keyword
Cox regression, occupation, standardized incidence ratio, standardized mortality ratio
National Category
Environmental Health and Occupational Health
Research subject
Occupational and Environmental Medicine
Identifiers
urn:nbn:se:umu:diva-81789 (URN)10.1136/oemed-2014-102251 (DOI)000356298200012 ()
Note

Originally published in manuscript form with the title A comparison between standard methods and structural nested modeling when adjusting for the healthy worker survivor effect. 

Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2017-12-06Bibliographically approved

Open Access in DiVA

fulltext(757 kB)693 downloads
File information
File name FULLTEXT01.pdfFile size 757 kBChecksum SHA-512
a3c825607d3c4f453aed50c4ecf982301ecf2285f3a016c923b93602add9d589ed809a9f86ceaea35ae8ec9e2516343a1d61123ffee7184dbcc583119e698f76
Type fulltextMimetype application/pdf

Authority records BETA

Björ, Ove

Search in DiVA

By author/editor
Björ, Ove
By organisation
Occupational and Environmental Medicine
Environmental Health and Occupational Health

Search outside of DiVA

GoogleGoogle Scholar
Total: 693 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 872 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf