Abstract
ObjectivesTo estimate the relationship between exposure to extremely low-frequency electromagnetic fields (ELF-EMF) and the risk of amyotrophic lateral sclerosis (ALS) by a meta-analysis.MethodsThrough searching PubMed databases (or manual searching) up to April 2012 using the following keywords: “occupational exposure”, “electromagnetic fields” and “amyotrophic lateral sclerosis” or “motor neuron disease”, seventeen studies were identified as eligible for this meta-analysis. The associations between ELF-EMF exposure and the ALS risk were estimated based on study design (case-control or cohort study), and ELF-EMF exposure level assessment (job title or job-exposure matrix). The heterogeneity across the studies was tested, as was publication bias.ResultsOccupational exposure to ELF-EMF was significantly associated with increased risk of ALS in pooled studies (RR = 1.29, 95%CI = 1.02–1.62), and case-control studies (OR = 1.39, 95%CI = 1.05–1.84), but not cohort studies (RR = 1.16, 95% CI = 0.80–1.69). In sub-analyses, similar significant associations were found when the exposure level was defined by the job title, but not the job-exposure matrix. In addition, significant associations between occupational exposure to ELF-EMF and increased risk of ALS were found in studies of subjects who were clinically diagnosed but not those based on the death certificate. Moderate heterogeneity was observed in all analyses.ConclusionsOur data suggest a slight but significant ALS risk increase among those with job titles related to relatively high levels of ELF-EMF exposure. Since the magnitude of estimated RR was relatively small, we cannot deny the possibility of potential biases at work. Electrical shocks or other unidentified variables associated with electrical occupations, rather than magnetic-field exposure, may be responsible for the observed associations with ALS.
Highlights
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder that results in the loss of motor neurons, and a rapidly progressive and fatal muscle paralysis
Selection criteria The selected studies were required to meet all the following criteria: (1) each included study must be an unrelated case-control or cohort study and only the one with a larger sample size was selected if studies had partly overlapping subjects; (2) the studies should refer to the association between occupational extremely low-frequency electromagnetic fields (EMF) (ELF-EMF) exposure and ALS risk; and (3) the outcome should be defined as a medical diagnosis of ALS or registered as ALS on the death certificate
Electrical shocks or other unidentified variables associated with electrical occupations, rather than magnetic-field exposure, may distort real association between ELF-EMF and ALS risk [12]
Summary
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder that results in the loss of motor neurons, and a rapidly progressive and fatal muscle paralysis. Epidemiological studies have suggested that exposure to various agents in the workplace, such as lead, aluminum, pesticides, electromagnetic fields (EMF), and electrical shocks, is associated with motor neuron degeneration [4,5,6,7]. Studies over the past two decades have shown that occupational exposure to extremely low-frequency EMF (ELF-EMF) may be a causal factor of ALS [6]. In 1986, Deapen and Henderson first reported an increased risk of ALS among people with occupations related to electricity and electronics [8]. Studies in the 1990s consistently reported an association between occupational ELF-EMF exposure and ALS risk; the relevant reports in the 2000s are controversial. The relationship between ELF-EMF exposure and increased risk of ALS is still questionable in the occupationally-exposed population
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