Risk of cancer among Danish utility workers--a nationwide cohort study

Our plain-English summary of Risk of cancer among Danish utility workers--a nationwide cohort study, by C. Johansen, J.H. Olsen (American Journal of Epidemiology, 1998).

The study

• Authors: C. Johansen, J.H. Olsen
• Journal: American Journal of Epidemiology
• Published: 1998;147(6):548-55
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The authors report the incidence of cancer in a large cohort of employees identified from all 99 Danish utility companies. Personal data and information on employment and exposure to magnetic fields and asbestos were obtained from manual files at the companies, the Danish Supplementary Pension Fund, and the public payroll administration. A total of 32,006 individuals with more than 3 months of employment were linked with the files of the Danish Cancer Registry. The period of follow-up for cancer occurrence among the employees was from April 1968 through December 1993 in the study conducted from 1994 to 1997. Overall, 3,008 cancers were observed, with 2,825 expected, yielding a small but significantly increased risk of 1.06 (95% confidence interval 1.03-1.10) among the utility workers in comparison with the general population. No excess was observed for all leukemias or for cancers of the brain or breast among men or women. There was no association of electromagnetic field exposure with risk of these cancers, even when the level and length of exposure to magnetic fields were taken into account. Increased risks for cancers of the lung and pleural cavity were seen mainly for workers whose jobs involved exposure to asbestos. The results from this study do not support the hypothesis of an association between occupational exposures to magnetic fields in the electric utility industry and the risk for cancer.

In plain English

This nationwide cohort study followed 32,006 people (26,135 men, 5,871 women) who worked at least 3 months at Denmark's 99 electric utility companies. It compared their cancers from April 1968 through December 1993 with rates in the general population. Magnetic-field and asbestos exposure were estimated from job title and work area. Asbestos jobs were classed only as no exposure or above-average exposure, without measurements. Overall, 3,008 cancers occurred versus 2,825 expected, an observed-to-expected ratio of 1.06 (95% confidence interval 1.03-1.10). No excess of leukemia or brain cancer was seen. Men had an excess of cancer of the pleural cavity (36 cases, ratio 3.2) and of lung cancer (523 cases, ratio 1.1). Women had an excess of lung cancer (34 cases, ratio 1.5). Among men, the pleural cancer ratio was 5.2 (19 cases) in asbestos-exposed jobs and 2.3 (17 cases) in jobs presumed unexposed. The authors said this indicates asbestos may have been more widespread than their classification predicted. The authors concluded the study did not support a link between occupational magnetic-field exposure and cancer, and that the lung and pleural excesses seemed to reflect past asbestos exposure.

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: Nationwide retrospective cohort study using record linkage to the Danish Cancer Registry, with observed cancers compared with numbers expected from national rates (standardized incidence ratios)
• Who was studied: 32,006 employees (26,135 men and 5,871 women) with at least 3 months of employment at any of the 99 Danish utility companies, followed for cancer from April 1, 1968 (or first employment) to December 31, 1993; about 526,000 person-years
• Exposure: Work in electric utilities. Exposure to 50-Hz magnetic fields was estimated by a job-exposure matrix. Asbestos was estimated by a simpler matrix with two categories (no exposure and above-average exposure), with no direct asbestos measurements. Fiber types were not specified. By Table 2, 34% of men and 4% of women were classed as above-average asbestos exposure.
• Main results:
  • All cancers, whole cohort: 3,008 observed versus 2,825 expected, SIR 1.06 (95% confidence interval 1.03-1.10)
  • Men: statistically significant excess of cancer of the pleural cavity, SIR 3.2 based on 36 cases (Table 3: 11 expected)
  • Lung cancer was increased in men (SIR 1.1, 523 cases) and women (SIR 1.5, 34 cases)
  • The excesses of lung and pleural cavity cancer were confined mainly to workers in jobs involving asbestos exposure. Table 6 (men): asbestos-exposed jobs had lung cancer 199 observed, SIR 1.3, and pleural cancer 19 observed, SIR 5.2. Jobs presumed unexposed had lung cancer 324 observed, SIR 1.1, and pleural cancer 17 observed, SIR 2.3.
  • The increased pleural cavity cancer risk among men presumed not exposed to asbestos indicated, per the authors, that asbestos may have been more widespread than the job-exposure matrix predicted
  • No excess risk for leukemia or brain cancer, and no link between cumulative magnetic-field exposure and these tumor types
• The authors' conclusion: The authors concluded that no associations were found between magnetic-field exposure and cancers previously linked with it. In their view, the increased risks for cancers of the lung and pleural cavities seemed to reflect previous exposure to asbestos.
• Limitations the authors state:
  • Job histories could not be ascertained precisely and the magnetic-field matrix was general, so some misclassification of exposure may have occurred
  • The asbestos job-exposure matrix appears to have underestimated how widespread asbestos exposure was, since pleural cancer was also increased among presumed unexposed workers

Topics

The National Library of Medicine indexes this study under subjects our site covers: Power plants and utilities.

Medical terms in this study, explained in our Lexicon: Cohort Study, Cancer Registry, confidence interval, Pleural Cavity, Occupational Exposure.

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