Occupational Exposure to Silica May Increase Risk of ALS, Study Suggests

Occupational exposure to silica is linked to a significantly increased risk of amyotrophic lateral sclerosis (ALS), a population-based study suggests.

The study “Multicentre, population-based, case-control study of particulates, combustion products and amyotrophic lateral sclerosis risk” was published in the Journal of Neurology, Neurosurgery, and Psychiatry.

The cause of ALS is still unknown, but both genetic and environmental factors are known to be at play. Farmers, veterinarians, firefighters, flight attendants, and truck drivers have been shown to have increased risk of ALS. Exposure to silica and asbestos, animal contact, and combustion products could explain the link between certain occupations and ALS.

Researchers at University Medical Centre Utrecht (Holland) recruited ALS patients and age-, sex-, and residency-matched controls from five registries in the Netherlands, Ireland, and Italy. Participants’ educational level, smoking, alcohol habits, and lifetime job history were obtained using a validated questionnaire.

They analyzed 1,252 ALS patients and 2,590 controls, recruited between 2011 and 2014. The researchers analyzed occupational exposure to silica, asbestos, organic dust, contact with animals, endotoxins, polycyclic aromatic hydrocarbons (agents released from burning coal, oil, gasoline, trash, tobacco, and wood) and diesel motor exhaust.

Compared to controls, ALS patients were more frequently exposed, at either low or high levels, to the occupational hazards. The analysis showed a statistically significant association between risk of ALS and high-level exposure to silica, organic dust, endotoxins and polycyclic aromatic hydrocarbons.

Low levels of exposure to silica and diesel motor exhaust were also significantly linked with ALS. The same was seen for continuous exposure to silica, diesel motor exhaust, and organic dust.

When combining the other exposures to silica, organic dust, or diesel motor exhaust, only silica remained linked with a significant increased risk for ALS.

Further analysis showed that the increased risk of ALS with the various types of exposures was the same in men and women. Silica remained a risk factor even after removing ALS patients with a mutation in the C9orf72 gene, the most common genetic cause of familial and sporadic ALS and frontotemporal dementia (FTD).

Overall, “in this large, multicentre, population-based, case-control study using full job histories, we found a positive association between occupational silica exposure and the risk of ALS,” the authors concluded.