Mercury has been linked with amyotrophic lateral sclerosis (ALS) and now a new study has found evidence that consumption of mercury-laden fish could increase risk of ALS.
Scientists are quick to reveal that while mercury-laden fish have been blamed for increased risk of ALS, regular consumption of fish and seafood is not associated with ALS. Previous studies have suggested mercury to be a risk factor for the disease and in the United States, the primary source of exposure to mercury is through eating fish contaminated with the neurotoxic metal.
Often referred to as Lou Gehrig’s disease, ALS is a progressive neurological disease that takes away the ability of nerve cells to interact with the body’s muscles. Early symptoms of the disease can include muscle twitching and weakness in a limb. It typically develops into complete paralysis of the body, including the muscles needed to speak, eat and breathe. There is no cure for ALS, and eventually the disease is fatal.
Researchers surveyed 518 people, 294 of whom had ALS, and 224 of whom didn’t, on how much fish and seafood they ate. Researchers estimated the annual exposure to mercury by looking up the average mercury levels in the types of fish and the frequency that the participants reported eating them.
Swordfish and shark are examples of fish that are considered high in mercury, while salmon and sardines typically have lower levels. Researchers also measured the levels of mercury found in toenail samples from participants with ALS and compared those levels to people without ALS.
Scientists found that among participants who ate fish and seafood regularly, those in the top 25 per cent for estimated annual mercury intake were at double the risk for ALS compared to those with lower levels. A total of 61 percent of people with ALS were in the top 25 percent of estimated mercury intake, compared to 44 percent of people who did not have ALS. They also found that higher mercury levels measured in toenail clippings were associated with an increased risk of ALS.
Those in the top 25 percent of mercury levels, based on fish-related intake or toenail clippings, were at a two-fold higher risk of ALS. These findings need to be replicated in additional studies.
The authors emphasize that this study does not negate the fact that eating fish provides many health benefits. However, the study suggests that the public may want to choose species that are known to have a lower mercury content, and avoid consuming fish caught in waters where mercury contamination is well-recognized. More research is needed before fish-consumption guidelines for neurodegenerative illness can be made.