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Epidemiological study (observational study)

Occupational exposure to extremely low-frequency magnetic fields and risk for central nervous system disease: an update of a Danish cohort study among utility workers.

Published in: Int Arch Occup Environ Health 2017; 90 (7): 619-628

Aim of study (acc. to author)

The association between occupational exposure to extremely low-frequency magnetic fields and risk for central nervous system disease was investigated in an update of a previous Danish cohort study (Johansen, 2000) among utility workers.

Further details

Two reference groups were chosen: men who had never worked in a utility company (external comparison) and utility workers with jobs that were considered not to be exposed, such as in administration (internal comparison to address healthy worker effect).

Endpoint/type of risk estimation

Type of risk estimation:
  • incidence
(incidence rate ratio (IRR))



Exposure groups

Reference group 1 magnetic field exposure: no (< 0.1 µT)
Group 2 magnetic field exposure: yes (≥ 0.1 µT)
Group 3 magnetic field exposure: medium (0.1 - 0.99 µT)
Group 4 magnetic field exposure: high (≥ 1.0 µT)


  • Group:
    • men
  • Age: ≥ 30 years
  • Characteristics: employees at all the 99 private and public utility companies
  • Observation period: 1982 - 2010
  • Study location: Denmark
  • Data source: Danish National Register of Patients

Study size

Total 45,188
Evaluable 32,006
Other: 665,083 person-years
Statistical analysis method:
  • Poisson regression model
( adjustment: )

Conclusion (acc. to author)

During the follow-up, 674 cases of dementia (all types), 44 of motor neurone disease, 213 of Parkinson disease, 80 of multiple sclerosis and 289 of epilepsy occurred in the cohort.
Among workers exposed to ≥ 0.1 μT compared with the Danish population, the incidence rate ratios for dementia, multiple sclerosis and epilepsy were not increased, but higher for motor neurone disease (IRR 1.24, CI 0.86-1.79) and lower for Parkinson disease (IRR 0.81, CI 0.67-0.97) . For the highest level of exposure (≥ 1.0 μT), increased incidence rate ratios were observed for dementia (IRR 1.44 CI 1.20-1.73), motor neurone disease (IRR 1.78, CI 0.93-3.43), multiple sclerosis (IRR 1.40, CI 0.79-2.46) and epilepsy (IRR 1.34; CI 0.99-1.82).
The authors conclude that elevated risks of dementia, motor neurone disease, multiple sclerosis and epilepsy and lower risks of Parkinson disease in relation to exposure to extremely low-frequency magnetic fields were observed in a large cohort of utility employees.

Study funded by

  • Danish Cancer Society
  • Danish Energy Agency (Energistyrelsen)

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