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.
Keywords: chemicals; electromagnetic fields; epidemiology; metals; physical activity.