Lung cancer in relation to employment in the electrical utility industry and exposure to magnetic fields

Our plain-English summary of Lung cancer in relation to employment in the electrical utility industry and exposure to magnetic fields, by D.A. Savitz, V. Dufort, B. Armstrong, et al (Occupational and Environmental Medicine, 1997).

The study

• Authors: D.A. Savitz, V. Dufort, B. Armstrong, G. Thériault
• Journal: Occupational and Environmental Medicine
• Published: 1997;54(6):396-402
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: A recent study found that lung cancer may be associated with exposures encountered in the electrical utility industry. To further evaluate this possibility, data were collected and analysed from five large electrical utility companies in the United States.

Methods: A cohort of 138905 male workers employed between 1950 and 1986 was followed up for mortality to the end of 1988, with 20733 deaths identified of which 1692 were due to lung cancer. Mortality from lung cancer was examined in relation to the duration of employment in specific jobs thought to have high exposure to 60 Hz magnetic fields and to an index of cumulative exposure to magnetic fields based on personal measurements. Exposure to pulsed electromagnetic fields (PEMFs) as estimated from another study was also considered. Poisson regression generated rate ratios for categories of exposure based on comparisons within the cohort adjusted for age, calendar year, race, socioeconomic status, work status, and estimated exposure to asbestos.

Results: Mortality rose modestly with duration of work as an electrician or power plant operator reaching rate ratios of 1.4 with > or = 20 years in those jobs but not with duration of work as a lineman or a combination of jobs thought to have high exposures to 60 Hz magnetic fields or PEMFs. Cumulative indices of exposure to 60 Hz magnetic fields and PEMFs were both associated with rate ratios of 1.2-1.3 in the highest intervals.

Conclusions: These data suggest that lung cancer is not strongly associated with duration of employment in specific jobs associated with high potential exposure to 60 Hz magnetic fields or to PEMFs. Small associations of lung cancer with indices of both 60 Hz magnetic fields and PEMFs leave open the possibility that larger associations have been diluted through exposure misclassification. Refined exposure assessment, especially to PEMFs, would be required to evaluate that possibility.

In plain English

This study followed 138 905 men employed at five US electrical utilities between 1950 and 1986 for deaths through 1988. Of 20 733 deaths, 1692 were from lung cancer. It asked whether jobs with high exposure to 60 Hz magnetic fields or to pulsed electromagnetic fields (PEMFs, estimated from another study) were linked to lung cancer. Asbestos was only adjusted for, by years in jobs judged to involve potential exposure, such as mechanic, electrician and pipe coverer. Overall, lung cancer deaths were slightly below the US male rate (SMR 0.91, 95% CI 0.87 to 0.95). Twenty or more years as a power plant operator gave a rate ratio of 1.43 (95% CI 1.05 to 1.96), and as an electrician 1.38 (0.97 to 1.95). Linemen showed little change. The highest cumulative PEMF exposure category gave 1.35 (1.07 to 1.69). The asbestos job index was positively associated with lung cancer, rate ratios never exceeding 1.5. Smoking data were unavailable, and the authors said the asbestos adjustment may have been incomplete. The authors concluded that lung cancer was not strongly associated with these jobs.

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: Retrospective cohort mortality study. Rate ratios were estimated by Poisson regression comparing more exposed with less exposed workers within the cohort. Standardised mortality ratios compared the cohort with US men.
• Who was studied: 138 905 male employees of five US electrical utility companies (Carolina Power and Light, Virginia Electric Power, PECO Energy, Tennessee Valley Authority, Pacific Gas and Electric). All worked full time at some point between 1950 and 1986 and had at least six months of continuous employment. They were followed to 31 December 1988. There were 20 733 deaths, 1692 of them from lung cancer, and 778 men were lost to follow up.
• Exposure: The main exposures were 60 Hz magnetic fields and PEMFs. Magnetic fields were assessed by job title (lineman, electrician, power plant operator) and by a cumulative index in microtesla-years based on 2842 personal measurements. PEMFs were estimated only by extrapolation from a Hydro-Quebec study. Potential asbestos exposure was assigned by job category, with no fiber type specified, and used only as an adjustment variable (years in these jobs, with a 10 year lag).
• Main results:
  • Total cohort compared with US men: 1692 lung cancer deaths against 1859.5 expected, SMR 0.91 (95% CI 0.87 to 0.95).
  • Power plant operators with 20 or more years in the job (57 cases): rate ratio 1.43 (95% CI 1.05 to 1.96), compared with person-years in no exposed job.
  • Electricians with 20 or more years in the job (39 cases): rate ratio 1.38 (95% CI 0.97 to 1.95).
  • Duration of work as a lineman had little effect on lung cancer risk (20 or more years: rate ratio 1.09, 95% CI 0.82 to 1.45).
  • Total cumulative 60 Hz magnetic field exposure (two year lag): rate ratios were around 1.1 in all categories above the control group.
  • Total cumulative PEMF exposure: lung cancer rate ratios were 1.3 to 1.4 above the background category, with little evidence of risk increasing as exposure increased. The highest category (196 cases) had a rate ratio of 1.35 (95% CI 1.07 to 1.69).
  • The index of years in jobs with potential asbestos exposure was positively associated with lung cancer, mainly at 20 or more years. Its rate ratios never exceeded 1.5 in the highest category.
• The authors' conclusion: The authors concluded that lung cancer is not strongly associated with duration of employment in jobs with high potential exposure to 60 Hz magnetic fields or PEMFs. They added that the small associations leave open the possibility that larger associations were diluted by exposure misclassification.
• Limitations the authors state:
  • No data on tobacco use were available.
  • The authors stated that confounding by smoking could conceivably produce rate ratios of 1.3 to 1.4.
  • Detailed information on asbestos exposure was not collected, so the asbestos adjustment may have been incomplete.
  • PEMFs were not measured directly. They were extrapolated from the Hydro-Quebec study, and there is uncertainty about what the positron meter actually measured.
  • The job exposure matrix assumed that present-day measurements apply to the same jobs in the past, and it grouped potentially heterogeneous jobs together.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Cumulative Exposure, rate ratio.

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