Introduction Amyotrophic lateral sclerosis (ALS) is a rare and complex neurodegenerative disease, which is highly fatal. It is known that 5%–10% of ALS cases are hereditary, but apart from this the causes for sporadic of ALS are unknown. Some evidence, however, suggests that manifestation and progression may be associated with certain occupational exposures, e.g. exposure to formaldehyde, lead and military service. The aim of this study is to survey the occupational risk of ALS in Denmark based on nationwide registries.

Methods We identified 1826 ALS cases who were 25 years old or less in 1964 and diagnosed from 1982 to 2013 from the Danish National Patient Registry, which cover all hospitals in Denmark. We matched 100 ALS free population controls to each case based on birth year and sex. Information on demographic data were obtained from the national Population Register and linked by the unique personal indentifier, assigned to all residents, to the Danish Pension Fund (DPF) to determine individual employment history from 1964. All employees in Denmark are compulsory members of DPF. Conditional logistic regression models were uses for estimation of odds ratios OR and their 95% confidence intervals, adjusted for socioeconomic status, marital status and residential location.

Results We observed increased OR of ALS among men who worked in e.g. agriculture, hunting, forestry or fishing (OR=1.2; 1.0–1.5). There was also a positive association for men employed in construction (OR=1.2; 1.1–1.4). In women, no significant increases were observed, but a protective association was seen with employment in the cleaning industry (OR=0.7; 0.5–0.9).

Conclusions Our study shows various occupations with exposure to toxicants, such as diesel exhaust and lead, and strenuous physical activity associated with increased odds of ALS in men. Future studies should have a particular focus on gathering detailed information on physical exertion and exposure to specific chemicals.