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Occupational Exposure to Electric Shocks and Magnetic Fields and Amyotrophic Lateral Sclerosis in Sweden
Heidi Fischer1, Leeka Kheifets, Anke Huss
1From the aDepartment of Epidemiology, Fielding School of Public Health, University of California Los Angeles, Los Angeles, CA; bInstitute for Risk Assessment Sciences, University of Utrecht, Utrecht, The Netherlands; cInstitute for Social and Preventive Medicine, University of Bern, Bern, Switzerland; dDepartment of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; eJulius Centre for Public Health Sciences and Primary Care, University Medical Centre, Utrecht, The Netherlands; fUnit of Occupational Medicine, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; gElectric Power Research Institute (EPRI), Palo Alto, CA; and hUnit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
Background:
Amyotrophic lateral sclerosis (ALS) has been consistently related to "electric occupations," but associations with magnetic field levels were generally weaker than those with electrical occupations. Exposure to electric shock has been suggested as a possible explanation. Furthermore, studies were generally based on mortality or prevalence of ALS, and studies often had limited statistical power.
Methods:
Using two electric shock and three magnetic field job-exposure matrices, we evaluated the relationship of occupational magnetic fields, electric shocks, electric occupations, and incident ALS in a large population-based nested case-control study in Sweden. Subanalyses, specified a priori, were performed for subjects by gender and by age (less than and more than 65 years).
Results:
Overall, we did not observe any associations between occupational magnetic field or electric shock exposure and ALS. For individuals less than 65 years old, high electric shock exposure was associated with an odds ratio (OR) of 1.22 (95% confidence interval [CI] = 1.03, 1.43). The corresponding result for the age group 65 years or older was OR = 0.92 (95% CI = 0.81, 1.05). Results were similar regardless which job exposure matrices, exposure definitions, or cutpoints were used. For electric occupations, ORs were close to unity, regardless of age. For welders, no association was observed overall, although for welders <65 years the OR was 1.52 (95% CI = 1.05, 2.21).
Conclusions:
In this very large population-based study based on incident ALS case subjects, we did not confirm previous observations of higher risk of ALS in electrical occupations, and provided only weak support for associations between electric shocks and ALS.
