Mortality from amyotrophic lateral sclerosis, other chronic disorders, and electric shocks among utility workers

Our plain-English summary of Mortality from amyotrophic lateral sclerosis, other chronic disorders, and electric shocks among utility workers, 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;148(4):362-8
• Cited by: 91 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Above-average exposure to electromagnetic fields has been associated with certain nonmalignant medical conditions such as amyotrophic lateral sclerosis, other neurologic diseases, depressive symptoms, and suicide. The authors conducted a nationwide mortality study in Denmark of 21,236 men employed in utility companies between 1900 and 1993. The causes of death were ascertained for January 1, 1974, through December 31, 1993, and cause-specific mortality was analyzed by latency and estimated levels of exposure to 50-Hz electromagnetic fields. Overall, 3,540 deaths were observed as compared with 3,709 expected from national mortality rates, yielding a standardized mortality ratio of 0.96 (95% confidence interval 0.93-0.99). A slight excess in mortality from cancer was due to deaths from cancers of the lung and pleural cavity, probably because of exposure to asbestos. A twofold increase in mortality from amyotrophic lateral sclerosis and a tenfold increase in mortality from electrical accidents were seen on the basis of 14 and 10 deaths, respectively, the former increasing with time since first employment in a utility company. The excess mortality from amyotrophic lateral sclerosis seems to be associated with above-average levels of exposure to electromagnetic fields and may be due to repeated episodes with electric shocks.

In plain English

This Danish study followed the deaths of 21,236 men who had worked at least 3 months for one of 99 electric utility companies between 1900 and 1993. Causes of death from 1974 through 1993 were compared with national death rates. The exposure studied was estimated workplace exposure to 50-Hz electromagnetic fields. Cancer deaths were slightly raised (standardized mortality ratio 1.1, 95% confidence interval 1.0-1.2). This was mainly because of a statistically significant excess of deaths from lung cancer (343 deaths) and cancer of the pleural cavity (14 deaths). The authors said this matched their earlier cancer study of these workers, in which the excess was more closely associated with estimated asbestos exposure than with electromagnetic fields. There were 14 deaths from amyotrophic lateral sclerosis (ALS) against 6.9 expected (ratio 2.0, interval 1.1-3.4), and 10 deaths from electrical accidents against 0.6 expected. The authors concluded that the ALS pattern suggested an association with jobs entailing medium to high exposure, possibly due to more episodes of electric shock. They cautioned that death certificates may misclassify neurodegenerative diseases.

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 cohort mortality (follow-up) study comparing observed deaths with deaths expected from national cause-specific mortality rates (standardized mortality ratios)
• Who was studied: 21,236 men with at least 3 months of employment at 99 Danish electric utility companies between 1900 and 1993, followed for cause of death from January 1, 1974 to December 31, 1993
• Exposure: Estimated average workplace exposure to 50-Hz electromagnetic fields. It was assigned by a job-exposure matrix of job title and work area and grouped as background, low, medium, high or unknown. Asbestos exposure was raised only in interpreting the lung and pleural cancer results, with reference to the authors' earlier study.
• Main results:
  • In the whole cohort, 3,540 deaths were observed against 3,709 expected (standardized mortality ratio 0.96, 95% confidence interval 0.93-0.99)
  • Mortality from all cancers combined was moderately increased in the cohort (standardized mortality ratio 1.1, 95% confidence interval 1.0-1.2)
  • The cancer increase was mainly due to a statistically significant excess of deaths from lung cancer (343 deaths) and cancer of the pleural cavity (14 deaths)
  • The authors stated that the lung and pleural cancer excess was in line with their previous cancer incidence study of these workers. In that study, the excess risk was more closely associated with estimated asbestos exposure than with workplace electromagnetic field exposure.
  • In the whole cohort there were 14 deaths from amyotrophic lateral sclerosis (ALS) against 6.9 expected (standardized mortality ratio 2.0, 95% confidence interval 1.1-3.4)
  • Among men in the medium and high exposure categories combined, there were 9 ALS deaths against 3.6 expected (standardized mortality ratio 2.5, 95% confidence interval 1.1-4.8)
  • In the whole cohort there were 10 deaths from accidents caused by electricity against 0.6 expected
  • Among employees in the high exposure category, overall mortality was increased (standardized mortality ratio 1.12, 95% confidence interval 1.04-1.19). This was mainly due to cancers of the lung and pleural cavity and accidents caused by electricity.
• The authors' conclusion: The authors concluded that the pattern of ALS mortality suggests an association within jobs entailing medium to high exposure to 50-Hz electromagnetic fields, possibly due to an increased number of electric shock episodes
• Limitations the authors state:
  • Misclassification of neurodegenerative diseases on death certificates could not be excluded and may be severe
  • The ALS estimate for 30 or more years since first employment was based on only six cases
  • The authors could not construct an exposure scale that separated exposure to electric shocks from exposure to electromagnetic fields

Topics

Medical terms in this study, explained in our Lexicon: Latency, standardized mortality ratio (SMR), confidence interval, Pleural Cavity.

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