Eating fish with high mercury content may be associated with ALS

Written by Jonathan Wilkinson

Researchers from Dartmouth College (NH, USA) have reported that consuming fish and seafood with higher levels of mercury may be linked to an increased risk of developing amyotrophic lateral sclerosis (ALS). However, eating this type of food as a regular part of the diet was not associated with ALS. These findings are based on the outcomes of a preliminary study that will be presented at the American Academy of Neurology’s 69th Annual Meeting (Boston, USA) being held 22–28  April 2017.
This research built upon previous studies that have indicated that mercury could be a risk factor for ALS. Specifically in the USA, the primary source of exposure to mercury is through eating fish contaminated with this metal. Elijah Stommel (Dartmouth College), one of the study investigators, explained: “For most people, eating fish is part of a healthy diet. But questions remain about the possible impact of mercury in fish.”

In this study, a survey was carried out regarding the fish and seafood eating habits of 518 people, 294 of whom had ALS, and 224 of whom did not. The study participants were required to report what kinds of fish they ate, and whether they were purchased from a store or caught while fishing. The annual exposure was then calculated by looking up the average mercury levels in the types of fish consumed and the frequency that the participants reported eating them. In addition to this, the investigators measured the levels of mercury found in toenail samples from participants with ALS and compared those levels to people without ALS.

It was found that among participants who ate fish and seafood regularly, those in the top 25% for estimated annual mercury intake were at double the risk for developing ALS compared to those with lower levels. Of the individuals with ALS, 61% were in the top 25% of estimated mercury intake, compared with 44% of people who did not have ALS. Additionally, higher mercury levels measured in toenail clippings were associated with an increased risk of ALS. Those in the top 25% of mercury levels, based on fish-related intake or toenail clippings, were at a twofold higher risk of ALS.

It is important to note that until further research has been performed, no guidelines can be published for the consumption of fish and the potential associations with neurodegenerative disease. However, the US FDA does advise that women of childbearing age and children should  eat two or three weekly meals of fish such as salmon or sardines, which have low mercury; in addition, they recommend avoiding fish with the highest mercury levels, such as shark and swordfish. The authors of this latest study emphasize that while eating fish provides a number of health benefits, consumers should consider eating the species that are known to have lower mercury content.

Sources: Mercury in fish, seafood may be linked to higher risk of ALS. Presented at: American Academy of Neurology’s 69th Annual Meeting, Boston, USA, 22–28  April 2017; www.aan.com/PressRoom/Home/PressRelease/1522