Mercury in Fish and Seafood May Be Linked to Higher Risk of Amyotrophic Lateral Sclerosis
April 18, 2017—Boston, Massachusetts—Eating fish and seafood with higher levels of mercury may be linked to a higher risk of amyotrophic lateral sclerosis. Fish and seafood consumption as a regular part of the diet was not associated with amyotrophic lateral sclerosis, however.
This conclusion, based on results of a preliminary study, will be reported at the American Academy of Neurology’s 69th Annual Meeting, from April 22 to 28.
Elijah Stommel, MD, PhD, of Dartmouth College, Hanover, New Hampshire, said, “For most people, eating fish is part of a healthy diet, yet questions remain about the possible impact of mercury in fish.”
While the exact cause of amyotrophic lateral sclerosis is unknown, studies have suggested mercury to be a risk factor for the disease. In the US, the primary source of exposure to mercury is fish contaminated with the neurotoxic metal.
Dr. Stommel and colleagues surveyed 518 individuals, 294 who had amyotrophic lateral sclerosis, and 224 who did not. They were asked how much fish and seafood they ate. Participants reported the types of fish they ate and whether they were purchased from stores or caught. The team estimated their annual exposure to mercury by researching average mercury levels in fish they ate and the frequency at which they ate them.
Swordfish and shark are considered high in mercury, while salmon and sardines harbor lower levels. The investigators also measured levels of mercury found in toenail samples from participants with amyotrophic lateral sclerosis and compared those levels to subjects without amyotrophic lateral sclerosis.
Among participants who ate fish and seafood regularly, those in the top 25% of estimated annual mercury intake were at double the risk for amyotrophic lateral sclerosis vs those with lower levels. Sixty-one percent of patients with amyotrophic lateral sclerosis were in the top 25% of estimated mercury intake vs 44% of subjects without amyotrophic lateral sclerosis.
Higher mercury levels measured in toenail clippings were associated with increased risk of amyotrophic lateral sclerosis. Those in the top 25% of mercury levels, based on fish-related intake or toenail clippings, were at a twofold higher risk of amyotrophic lateral sclerosis. The findings need to be replicated in additional studies.
Dr. Stommel emphasized that the study results do not negate the fact that eating fish provides many health benefits. The results suggest, however, that the public may want to choose species known to harbor 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 drafted.
FDA recommendations for women of childbearing age and children are two to three weekly meals of species such as salmon or sardines that harbor low mercury but are high in nutrients such as potentially beneficial omega-3 fatty acids. The FDA recommends avoiding fish with the highest mercury levels, such as shark and swordfish. Waterbody-specific fish advisories can be checked prior to consuming fish caught by family and friends.