Occupational pesticide exposure may significantly increase ALS risk

Workplace exposure to pesticides (herbicides and insecticides) is linked to a 60-70% heightened risk of the most common form of motor neuron disease-amyotrophic lateral sclerosis, or ALS for short, finds a synthesis of the available evidence, published online in Occupational & Environmental Medicine.

Men who have been exposed to these chemicals may be twice as likely to develop the condition as those who haven't been, the analysis indicates.

Although still relatively rare, the incidence of ALS-a progressive and rapidly fatal neurodegenerative disease for which there is no cure-has increased in recent years, note the researchers.

White the short term neurotoxic effects of pesticides, particularly insecticides, have been known for decades, there's not a great deal of evidence on their potential long term neurotoxicity, they add.

In a bid to strengthen the evidence base, the researchers scrutinised research databases for relevant studies, including peer reviewed theses and scientific reports, on workplace exposure to pesticides and ALS, published between 1990 and 2025.

Eight case-control studies involving a total of 1734 cases of ALS, and 3 studies

involving 457 cases of unspecified motor neuron disease, were retained for pooled data

analysis from 767 initially screened articles.

This showed that compared with no exposure, any workplace exposure to pesticides was associated with a 60% heightened risk of ALS, based on the pooled data from 6 studies. 

And based on the results of 3 studies, any exposure to high levels of pesticides was associated with a near tripling in risk compared with no pesticide exposure, whereas any exposure to lower levels was associated with a doubling in risk.

Compared with no exposure, exposure to herbicides was associated with a 70% heightened risk of developing the disease; exposure to either insecticides or fungicides was associated with a 60% heightened risk.

In studies that reported risk estimates stratified by sex, the pooled data analysis showed that exposed men were twice as likely as unexposed men (3 studies) to develop ALS. 

But no increased risk was apparent in women who had been exposed to pesticides compared with those who hadn't been.

The researchers highlight various limitations to their findings: the small number of available primary studies and their crude assessment of exposure, generally based on answers to a few limited questions. 

"To strengthen the evidence on risk factors for ALS, primary studies particularly need methodological improvements on exposure assessment, on the selection of reference groups, and on adjustment for potential confounders, including analysis for interactions between risk factors," they emphasise.

But they conclude: "The findings of this review add to the evidence that occupational exposure to pesticides may increase the risk of ALS and should encourage the implementation of interventions aimed at reducing exposure during occupational pesticide use."