Holding a job in mechanics, painting, or construction also significantly increase the chances of developing the disease, researchers noted.
The study, “Risk Factors for Amyotrophic Lateral Sclerosis: A Regional U.S. Case‐Control Study,” was published in the journal Muscle and Nerve.
A large number of environmental factors are thought to increase the risk of ALS, including the use of herbicides, exposure to environmental pollution, heavy metals and a neurotoxic molecule produced by blue-green algae, and working with silica.
But evidence for each of these factors is inconsistent, and none has been identified as a definite cause of the disease.
To determine additional environmental risk factors that might contribute to ALS, researchers based at multiple U.S. sites conducted a regional case control study involving 188 ALS patients living in northern New England and Ohio.
As controls, the group included 376 people living in the same regions as patients, and matched to patients in terms of age, sex, race, and smoking status. Participants were at least 21 years old, and most (46%) were in the age range of 50–65.
Participants were asked to fill out questionnaires detailing their lifestyle and environmental exposure. Hobbies, activities, and occupational factors of the participants were included in the survey. Participants also reported the amount of time and frequency of these activities.
Results showed that a history of head trauma or concussion that caused a “blackout” was associated with increased odds of having ALS, but that association reached significance only in people who experienced one head trauma — and not multiple ones.
Head trauma was not significantly associated with ALS if injuries occurred less than 10 years before diagnosis, but it was a factor if the injury happened 10 or more years prior to diagnosis. The odds of having ALS were the greatest (1.9 times higher than in patients without head trauma) when the last injury occurred 40 or more years before the diagnosis.
Compared to controls, twice as many ALS patients reported having severe electrical burns or having been electrocuted. As observed with head trauma, electrical burns happening within 10 years of diagnosis did not raise the odds of ALS, but those occurring in earlier years did increase those odds significantly — by 3.1 times. Burns occurring after age 30 also were significantly associated with ALS.
Hobbies involving lead were most often associated with ALS. These included casting lead bullets, making stained glass with lead joints, and using lead fishing sinkers; a significant association was observed most often for lead bullets. Also, only exposure to lead for 20 or more years before diagnosis significantly raised the odds of ALS.
The study asked the participants to list up to five of their past occupations. Holding a job in mechanics, painting, or construction was associated with increased odds of ALS, compared to all other job categories pooled together.
When examining sex differences, head injuries and lead exposure were similar between men and women.
“Overall, our results support previous reports of head injury, electric shock, lead exposure, and certain occupations as ALS risk-factors,” the researchers wrote. “Our findings of the long interval between exposures and the diagnosis of ALS are particularly important. Some exposures, 20 or more years before diagnosis, had the largest effects on ALS risk.”
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