Objective To prospectively study suspected occupational
risk factors for amyotrophic lateral sclerosis (ALS).
Methods For this case–cohort analysis within the
prospective Netherlands Cohort Study, 58 279 men
and 62 573 women aged 55–69 years at enrolment in
1986 were followed up for 17.3 years on ALS mortality.
Information on occupational history and potential
confounders were collected at baseline through a selfadministered
questionnaire and entered for a random
subcohort (2092 men and 2074 women) and ALS deaths
(76 men and 60 women). Occupational exposure to
solvents, pesticides, metals, extremely low frequency
magnetic fields (ELF-MFs) and electrical shocks was
estimated by means of job exposure matrices (JEMs).
Associations between ever/never occupationally exposed
and cumulative exposure and ALS mortality were
analysed by gender using Cox regression.
Results Occupational exposure to ELF-MF showed a
possible association with ALS mortality among men:
HR for ever holding a job with high exposure versus
background 2.19 (95% (CI): 1.02 to 4.73) and HR
for the highest tertile of cumulative exposure versus
background 1.93 (95% CI 1.05 to 3.55).
Interpretation These results strengthen the evidence
suggesting a positive association between ELF-MF
exposure and ALS. We did not replicate earlier positive
findings for other occupational exposures.
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