For the study, the researchers surveyed around 500 people, 294 people with ALS and 224 without it. Participants were asked about their eating habits concerning fish and seafood, and whether they caught it themselves or bought it. Then the researchers estimated how much mercury the participants consumed each year. They also tested participants’ toenail clippings for mercury content.
After the analysis, the scientists found that 61% of those with ALS were in the top quarter of mercury consumption, compared to 44% of those without ALS. However, the study only establishes a link between the two and does not find a cause-and-effect relationship.