Occupational exposure to pesticides increases the risk of amyotrophic lateral sclerosis: a systematic review and meta-analysis

Abstract

Objective To systematically review the evidence on the association between occupational exposure to pesticides and the risk of amyotrophic lateral sclerosis (ALS). Methods A systematic search, conducted in eight bibliographic databases for publications between 1990 and 2025, identified observational studies estimating the risk of ALS after occupational pesticide exposure. Study quality was assessed using the WHO Risk of Bias (RoB) assessment instrument for systematic reviews, with the ROBINS-E (RoB in non-randomised studies of exposure) tool domains of bias. Pooled risk estimates were produced using random-effects models with restricted maximum likelihood, heterogeneity was assessed with I² statistics, and meta-regressions and publication bias explored with funnel plots and Egger’s test. Results Eight case-control studies (1734 cases) were retained for meta-analysis from 767 initially screened articles. ‘Ever’ occupational exposure to pesticides was associated with an increased risk of ALS (n=6 studies, pooled OR (pOR)=1.6; 95% CI 1.1, 2.2; I²=57%), for combined sexes. The risk for exposure to herbicides was slightly greater (pOR=1.7, I 2 =0.0%) than for exposure to insecticides or fungicides (pORs=1.6, I 2 =0.0%). Based on three studies, ever exposure to high levels of pesticides was associated with a higher risk (pOR=2.7; 95% CI=1.4, 5.0) than exposure to low levels (pOR=1.9; 95% CI=1.0, 3.7). Self-reported exposure assessment methods and older publication dates (<2015) were statistically significant predictors of the effect size. Conclusion Despite the small number of studies and some heterogeneity, our results add to the evidence suggesting that occupational exposure to pesticides may increase the risk of ALS.