Occupational exposure and amyotrophic lateral sclerosis in a prospective cohort
By: Tom Koeman, Pauline Slottje, Leo J Schouten, Susan Peters, Anke Huss, Jan H Veldink, Hans Kromhout, Piet A van den Brandt, Roel Vermeulen
Published in: Occupational and Environmental Medicine
This case-cohort study investigated whether occupational exposure to extremely low frequency (ELF) magnetic fields (MFs) is associated with a motor neuron disease. The study was conducted as a subset of a cohort study that included more than 120,000 subjects that were enrolled in the study in 1986 and followed for 17 years for amyotrophic lateral sclerosis (ALS) mortality. The subset case-cohort study included 136 ALS deaths and 4166 controls drawn randomly from the cohort (called subcohort). The information on a lifetime occupational history was obtained via questionnaires and the occupational exposure to ELF MFs of each subject was assessed via a job-exposure matrix (JEM). Information on other occupational exposure was also obtained including electrical shocks, metals, and several chemical agents. The association between high exposure to ELF MFs and ALS was found to be statistically significant only in men (hazard ratio = 2.19, 95% confidence interval = 1.02 – 4.73). The authors concluded that their study supported an association between occupational ELF-MF exposure and an increased risk of ALS mortality.
Several studies have investigated whether occupational exposure to ELF MFs is associated with neurodegenerative diseases, particularly Alzheimer’s disease and ALS. Meta-analyses of previous studies have reported a possible increased risk between occupational ELF fields and ALS but the results are largely inconsistent and many of the studies have methodological weaknesses, mainly in the assessment of exposure and the possibility of confounding from other occupational exposures including electric shocks and other chemical and physical agents. The current study goes a long way into addressing some of the short comings of previous studies; it is a large prospective study of the general population, it has used the best available JEM to assess occupational ELF fields and has looked at other occupational exposures. The study has some limitations which were acknowledged by the authors including that the JEM used may not truly represent the exposure experienced by the subjects. The conclusion by the authors that the study adds support for an association between occupational ELF magnetic fields and ALS mortality is valid however as acknowledged by the authors this is an observational study so no firm conclusions can be drawn on whether occupational ELF fields do cause ALS. Further research in this area is needed particularly in the assessment of exposure.