Background Previous studies have identified increased risks of amyotrophic lateral sclerosis (ALS) in electrical workers, but studies assessing risk in workers exposed to magnetic fields were ambiguous. Electric shocks have been hypothesised to be the relevant exposure, but potential risks from electric shocks have not been previously disentangled from those of magnetic fields. We aimed at analysing the association of ALS with both magnetic field exposure as well as risk of electric shocks at work.
Methods We used the Swiss National Cohort study, which is based on census information from 1990 and 2000 linked with mortality records from 2000–2008. High or medium versus low exposure to magnetic fields and risk of electric shocks was assigned to occupations using two job exposure matrices. Data of 4.7 million persons were analysed using Cox proportional hazard models and adjusted for age, sex, educational level, civil status, nationality, language region, degree of urbanity of the municipality and an area-based proxy for socioeconomic position.
Results During 2000–2008, 1313 persons with information on occupation died from ALS. Hazard ratios were around unity for persons exposed to magnetic fields or risk of electric shocks in either 1990 or 2000. In persons classified as medium or high exposed in both 1990 and 2000, a slight increase in mortality from ALS was observed for magnetic field exposures (HR 1.39, 95% CI 1.03–1.87), but less so for electric shocks (HR 1.20, 95%CI 0.88–1.65). When accounting for both exposures in the same model, magnetic fields had a similar HR (1.36, 95%CI 0.99–1.89) as before, but the HR for electric shocks was attenuated to 1.07 (95%CI 0.76–1.5).
Conclusions We observed an association of long-term exposure to extremely low frequency magnetic fields and mortality from ALS, but not of risk of electric shocks and ALS.
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