Epidemiological study

Associations of Occupational Exposures to Electric Shocks and Extremely Low-Frequency Magnetic Fields With Motor Neurone Disease epidem.

By: Chen GX, 't Mannetje A, Douwes J, Berg LH, Pearce N, Kromhout H, Glass B, Brewer N, McLean DJ

Published in: Am J Epidemiol 2021; 190 (3): 393-402

Aim of study (acc. to author)

A case-control study was conducted in New Zealand to investigate the associations between occupational exposure to electric shocks, extremely low-frequency magnetic fields (ELF-MF) and motor neurone disease.

Further details

in a previous study by Chen et al. (2019) was observed that both electricians and telecommunication technicians (among other occupations) had elevated risks of motor neuron disease. In the present study the occupational lifetime exposure was assessed using the job exposure matrix for extremely low frequency magnetic fields by Koeman et al. (2013) and the job exposure matrix for electric shocks by Huss et al. (2013).

Endpoint/type of risk estimation

neurodegenerative diseases: motor neuron disease

Type of risk estimation:

incidence
prevalence

(odds ratio (OR))

Exposure

- electric injuries/electrocution
- occupational

Assessment

questionnaire: lifetime occupational history
job exposure matrix: JEMs for electrical shocks and extremely low frequency magnetic fields
calculation: cumulative exposure was expressed as unit-years, which was calculated as the product of the level of exposure and duration of years of each exposure, summed over the entire job history

Exposure groups

Group	Description
Reference group 1	electric shocks: never exposed above background level
Group 2	electric shocks: ever exposed above background level
Reference group 3	electric shocks: background level
Group 4	electric shocks: medium exposure only
Group 5	electric shocks: ever high exposure
Reference group 6	electric shocks: duration of exposure, background level
Group 7	electric shocks: duration of exposure < 3 years
Group 8	electric shocks: duration of exposure 3 - 8 years
Group 9	electric shocks: duration of exposure 9 - 24 years
Group 10	electric shocks: duration of exposure > 24 years
Reference group 11	electric shocks: cumulative exposure, background
Group 12	electric shocks: cumulative exposure 4 unit-years
Group 13	electric shocks: cumulative exposure 4 - 16 unit-years
Group 14	electric shocks: cumulative exposure 17 - 52 unit-years
Group 15	electric shocks: cumulative exposure > 52 unit-years
Reference group 16	extremely low frequency magnetic fields: never exposed above background level
Group 17	extremely low frequency magnetic fields: ever exposed above background level
Reference group 18	extremely low frequency magnetic fields: background level
Group 19	extremely low frequency magnetic fields: medium exposure only
Group 20	extremely low frequency magnetic fields: ever high exposure
Reference group 21	extremely low frequency magnetic fields: duration of exposure, background level
Group 22	extremely low frequency magnetic fields: duration of exposure < 3 years
Group 23	extremely low frequency magnetic fields: duration of exposure 3 - 8 years
Group 24	extremely low frequency magnetic fields: duration of exposure 9 - 23 years
Group 25	extremely low frequency magnetic fields: duration of exposure > 23 years
Reference group 26	extremely low frequency magnetic fields: cumulative exposure, background level
Group 27	extremely low frequency magnetic fields: cumulative exposure < 4 unit-years
Group 28	extremely low frequency magnetic fields: cumulative exposure 4 - 12 unit-years
Group 29	extremely low frequency magnetic fields: cumulative exposure 13 - 28 unit-years
Group 30	extremely low frequency magnetic fields: cumulative exposure > 28 Einheiten-Jahre

Population

Group:
- men
- women
Observation period: 2013 - 2016
Study location: New Zealand

Case group

Characteristics: patients with motor neuron disease diagnosed by a neurologist
Data source: MND Association of New Zealand register, National Minimum Dataset

Control group

Selection:
- population-based
Matching:
- sex
- age
- case:control = 1:2
Exclusion criteria: other neurodegenerative disease such as Parkinson's disease and Alzheimer's disease

Study size

	Cases	Controls
Participants	321	605
Participation rate	92 %	48 %
Evaluable	319	604

Statistical analysis method:

unconditional logistic regression

(adjustment:

5-year age group
sex
socioeconomic status
education
smoking status, alcohol consumption, ethnicity, sports, head injury, spine injury, exposure to solvents, ELF-MF resp. electrical injury

)

Results (acc. to author)

An elevated risk for motor neuron disease was observed for having ever worked in a job with potential for electric shocks (group 2: OR 1.35, CI 0.98-1.86), with the strongest association for the highest level of exposure (group 5: OR 2.01, CI 1.31-3.09). Analysis by duration of exposure suggested a non-linear association: risk was increased for both short-duration (<3 years) (OR 4.69, CI 2.25-9.77) and long-duration in a job with high level of electric shock exposure (>24 years; OR 1.88, CI 1.05-3.36), with less pronounced associations for intermediate durations.
No association between exposure to extremely low frequency magnetic fields and motor neuron disease was found.
The authors conclude that their findings provide support for an association between occupational exposure to electric shocks and motor neurone disease but did not show associations with exposure to work-related extremely low frequency magnetic fields.

Study funded by

Health Research Council of New Zealand

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