Epidemiological study (observational study)

Occupational Exposure to Electric Shocks and Magnetic Fields and Amyotrophic Lateral Sclerosis in Sweden.

Published in: Epidemiology 2015; 26 (6): 824-830

Aim of study (acc. to author)

A case-control study was conducted in Sweden to evaluate the association between occupational exposure to magnetic fields and electric shocks as well as electric occupations and the incidence of amyotrophic lateral sclerosis.

Further details

Occupational exposure was assessed by applying three magnetic field and two electric shock job exposure matrices.

Endpoint/type of risk estimation

Type of risk estimation:
  • incidence
(odds ratio (OR))



Exposure groups

Reference group 1 magnetic field exposure: low
Group 2 magnetic field exposure: medium
Group 3 magnetic field exposure: high
Reference group 4 risk for electrical shocks: low
Group 5 risk for electrical shocks: medium
Group 6 risk for electrical shocks: high
Reference group 7 no electric occupations
Group 8 electric occupations including welders
Group 9 welders


  • Group:
    • men
    • women
  • Age: ≥ 20 years
  • Observation period: 1991 - 2010
  • Study location: Sweden

Case group

Control group

  • living in Sweden
  • Selection:
    • population-based
  • Matching:
    • sex
    • birth year
    • case:control = 1:5

Study size

Cases Controls
Eligible 5,020 25,100
Evaluable 4,709 23,335
Statistical analysis method:
  • conditional logistic regression
( adjustment:
  • residential area
  • socioeconomic status
  • education

Conclusion (acc. to author)

Overall, no associations between occupational exposure to magnetic fields or electric shocks and the incidence of amyotrophic lateral sclerosis were observed. For individuals less than 65 years old, an increased risk was found with high electric shock exposure (OR 1.22, CI 1.03-1.43), however, not in the age group 65 years or older (OR 0.92, CI 0.81-1.05). Results were similar regardless which job exposure matrices, exposure definitions or cutpoints were used. No increased risk was found for electric occupations (including welders). For welders, no association was observed overall, although for welders less than 65 years an increased risk was observed (OR 1.52, CI 1.05-2.21). There was no evidence that electric shock was a confounder in the analyses of magnetic fields.
The authors concluded that previous observations of higher risk of amyotrophic lateral sclerosis in electrical occupations were not confirmed in this study and only weak support for associations between electric shocks and amyotrophic lateral sclerosis was provided.

Study funded by

  • Karolinska Institute, Sweden
  • Swedish Research Council (VR)
  • Centers for Disease Control and Prevention (CDC), USA
  • National Institute for Occupational Safety and Health (NIOSH), USA
  • Southern California NIOSH Education and Research Center, USA
  • Swedish Research Council for Health, Working Life and Welfare (Forte), Sweden

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