Exposure to electric shocks and extremely-low-frequency magnetic fields: The risk of amyotrophic lateral sclerosis

Background: Electrical occupations have been linked to an increased risk of amyotrophic lateral sclerosis (ALS) in multiple studies. The underlying mechanism is however not clear. We explored the association between occupational exposure to electric shocks and extremely lowfrequency magnetic fields (ELF-MF) and the risk of ALS in 3 population-based case-control studies. Methods: ALS patients and population-based controls were recruited in the Netherlands, Ireland and Italy, between 2010 and 2015, as part of the Euro-MOTOR project. Lifetime occupational and lifestyle histories were obtained using structured questionnaires. We applied 2 previously developed job exposure matrices assigning low (i. background), medium or high risk of electric injuries due to shocks and exposure to ELF-MF. Odds ratios (OR) and 95% confidence intervals (CI) for ALS were estimated by logistic regression for both occupational exposures in the same model, adjusted for age, sex, cohort, smoking status and alcohol drinking. Results: Complete occupational histories and information on confounding variables was available for 1423 confirmed ALS cases and 2851 controls. Among cases, 20% had ever been high exposed to electric shocks, and 7% had ever been high exposed to ELF-MF. Among controls, the proportions were 16% and 5%, respectively. Exposure to electric shocks and ELF-MF were only weakly correlated (Pearson correlation R=0.37). Both ever exposure to electric shocks (OR=1.23, 95% CI 1.05-1.44) and ELF-MF (OR=1.15, 95% CI 0.99-1.32) were associated with ALS. No difference between the level of exposure or a trend with duration of exposure was observed for either exposure. Conclusion: Our findings support a possible independent association between occupational exposure to electric shocks and ELF-MF and the risk of ALS.