Amyotrophic Lateral Sclerosis and Occupational Exposures: A Systematic Literature Review and Meta-Analyses

Abstract

Objectives: We conducted a systematic literature review to identify studies fulfilling good scientific epidemiological standards for use in meta-analyses of occupational risk factors for amyotrophic lateral sclerosis (ALS). Methods: We identified 79 original publications on associations between work and ALS. The MOOSE (Meta-analysis Of Observational Studies in Epidemiology) and GRADE (Grading of Recommendations, Assessment, Development and Evaluations) guidelines were used to ensure high scientific quality, and reliable protocols were applied to classify the articles. Thirty-seven articles fulfilled good scientific standards, while 42 were methodologically deficient and thus were excluded from our meta-analyses. Results: The weighted relative risks for the various occupational exposures were respectively; 1.29 (95% confidence interval (CI): 0.97–1.72; six articles) for heavy physical work, 3.98 (95% CI: 2.04–7.77; three articles) for professional sports, 1.45 (95% CI: 1.07–1.96; six articles) for metals, 1.19 (95% CI: 1.07–1.33; 10 articles) for chemicals, 1.18 (95% CI: 1.07–1.31; 16 articles) for electromagnetic fields or working with electricity, and 1.18 (95% CI: 1.05–1.34; four articles) for working as a nurse or physician. Conclusions: Meta-analyses based only on epidemiologic publications of good scientific quality show that the risk of ALS is statistically significantly elevated for occupational exposures to excessive physical work, chemicals (especially pesticides), metals (especially lead), and possibly also to electromagnetic fields and health care work. These results are not explained by publication bias.

Neurological and neurourological complications of electrical injuries

“…It is suggested that ALS pathogenesis might be triggered by recurrent minor or more serious electrical injuries. Although the reported evidence until now is not always supportive of the connection of ALS to electrical injury [82], current data overall tends to support this hypothesis [76,80,81].…”

“…The prevalence of ALS in electricity-related occupations seems to be increased according to different epidemiological studies [76,77], case series [78] and case reports [79]. History of electric shock has been listed as one of the main risk factors that may be associated with ALS in two recent metaanalyses [80,81]. It is suggested that ALS pathogenesis might be triggered by recurrent minor or more serious electrical injuries.…”

A Comparison of Mercury Exposure from Seafood Consumption and Dental Amalgam Fillings in People with and without Amyotrophic Lateral Sclerosis (ALS): An International Online Case-Control Study

“…Some occupational studies give indirect evidence that workplace exposure to mercury in factories may be implicated in ALS because men with ALS tend to have occupations involving lower skills and tasks, typically associated with factory workers [46]. A recent systematic review of occupational exposures in ALS lists 15 studies in which occupational exposure to toxic metals was reported [47]. In five of these, mercury was analysed as an individual metal [48,49,50,51,52], but case and control numbers were too small in all of these reports for robust statistical analyses.…”

Oxidative Stress, Neuroinflammation and Mitochondria in the Pathophysiology of Amyotrophic Lateral Sclerosis

“…Nevertheless, the involvement of many possible causal/risk factors has been suggested. This includes (but not limited to) chemicals, metals, radiation/electromagnetic fields, physical activity, dietary habits, viruses, bacteria, prions, fungi, protein-related abnormalities, mitochondria-related pathology, glutamate excitotoxicity, higher energy expenditure than intake and progressive impairment of glucose metabolism, microtubule mediated deficits in axonal transport, reactive phenotypes in astrocytes and microglia, autoimmunity, and moderate to severe traumatic brain injury [3,[6][7][8][9][10][11][12][13][14]…”