Mercury in fish a possible risk factor for ALS

Jul 29, 2017

Many of us eat fish as part of a healthy diet. Full of healthy fat and nutrients, it’s a staple for people around the globe. But there’s another side of fish that’s less positive -- a possible link between mercury in fish and ALS.

Joining us this week on “Take Care” are two researchers of a recent study that found that eating certain types of fish may increase the risk of developing ALS.  The researchers are Dr. Elijah Stommel, a professor of Neurology at the Geisel School of Medicine at Dartmouth College and a neurologist at Dartmouth-Hitchcock Medical Center; and Angeline Andrew, an assistant professor of neurology at the Geisel School in epidemiology and biostatistics and an experienced molecular epidemiologist.

The first thing Stommel says is that the research and findings of this study are not meant to scare people or prevent them from eating fish.

“We have this involved questionnaire that we’ve been having our ALS patients and a control group take over the last several years,” Stommel says. “We’re interested in looking at the question of whether eating fish might predispose patients to a disease like ALS.”

But why fish and why ALS? Fish are one of the main sources of organic mercury, according to Stommel, and mercury has been thought of as being a risk factor of the disease (along with other heavy metals).

“Fish were previously linked to ALS in a study in Lake Michigan a number of years ago,” according to Andrew. “So there was a precedent for potential issue with fish consumption. And then mercury is a known neurotoxic agent.”

The food chain

You might be wondering why mercury is found in fish in the first place. Remember the food chain you learned about in grade school? It goes something like this:

  • Mercury enters the water system
  • The mercury is taken up by very small organisms in the food chain
  • The very small organisms are eaten by small fish
  • The small fish are eaten by bigger fish, and on and on

If you would rather not eat fish with high levels of mercury, you should probably avoid fish at the top of the food chain, like shark, according to this week’s guests. Some fish that are relatively low in mercury are codfish, wild salmon, sardines and squid. Fish higher in mercury include swordfish and shark.

It is important to take the new findings for what they are, though, because there is a genetic disposition to ALS and the disease is still very rare, according to Stommel.

“I think the bottom line is ALS is a relatively rare disease. Most of us are never going to get the disease. And most of us that eat a lot of swordfish aren’t going to get the disease, but it probably is a risk factor -- eating mercury-laden fish.”