Evaluation of Occupational Exposure to Magnetic Fields and Motor Neuron Disease Mortality in a Population-Based Cohort

Over the past several decades, there has been continuing concern over whether exposure to extremely-low-frequency magnetic fields can adversely affect health. A recent review of the epidemiologic literature concluded that although occupational magnetic fields may increase the risk for some health outcomes, the evidence is not strong or consistent enough to draw firm conclusions.1 Nevertheless, continued research of the impact of magnetic field exposure on amyotrophic lateral sclerosis (ALS), which comprises more than 90% of all motor neuron disease (MND),2 was recommended on the basis of consistent evidence linking electrical occupations to an increased risk of ALS but weaker evidence based on measured magnetic field.1,3 The etiology for ALS is still largely unknown,4 but primarily animal studies have pointed toward oxidative damage, protein aggregation, mitochondrial dysfunction, and caspase-mediated apoptosis as possible causative mechanisms in the disease.5-8 Therefore, it is important to pursue leads regarding potential risk factors, including magnetic field exposure. It has been suggested that magnetic field exposure can result in neurological damage through increasing oxidative stress and inducing DNA breaks. The association between magnetic fields and oxidative DNA stress has been demonstrated in some studies9,10 but not others.11 A study by Falone and colleagues12 showed an interaction between rat age and magnetic fields in the decreasing activity levels of antioxidant enzymes, suggesting a susceptibility to oxidative stress from magnetic fields as the rats mature. As oxidative damage is thought to be involved in toxicity targeting motor neurons,13 it is possible that magnetic field exposure may result in motor neuron degeneration through this pathway. Nevertheless, the biological mechanism responsible for an association between magnetic fields and ALS, or the broader group of MND, remains unclear. We evaluated the association between quantitative levels of occupational magnetic field exposure and MND mortality in a population-based cohort representative of the general US population.