Mercury in Fish and Seafood Might Double Risk of ALS

assorted cuts of fish displayed at a fish marketALS, or amyotrophic laterals sclerosis, is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. This terrifying condition, also sometimes called Lou Gehrig’s disease, causes tremendous suffering as motor neurons between the brain, spinal cord, and muscles die off, and victims lose the ability to move, speak, and breathe. Symptoms usually begin with muscle weakness, then muscle twitching and, eventually, muscle wastage. ALS is always fatal. It usually strikes people between the ages of 40 and 70, and approximately 20,000 Americans have the disease at any given time according to the ALS Association.

Researchers are frantically searching for effective cures for ALS, but none has yet been identified. Some research has, however, uncovered possible risk factors to be avoided.

For example, some scientists believe ALS may be linked to environmental toxins, such as lead and pesticides. In line with that theory, a recent study suggests that consuming higher levels of mercury through fish and seafood may double your risk of ALS.

Mercury in the Diet and ALS

Although previous research has examined similar linkages, results have been conflicting. This most recent study—scheduled for discussion at April at the American Academy of Neurology’s 69th Annual Meeting in Boston—specifically examined the relationship between ALS and mercury in the diet through fish and seafood. The research team was headed up by Dr. Elijah Stommel, of Dartmouth College in Hanover, New Hampshire.

  • 518 participants took part in the trial, 294 with ALS and 224 without ALS
  • The team collected dietary information including types of seafood and fish consumed
  • Researchers then estimated the amount of mercury each person was likely to have ingested
  • Finally, the researchers even collected toenail samples from participants and analyzed them for their mercury content

Sashimi triDetailed accounting of diet was important, because fish species vary in levels of mercury. This is because mercury is not easily excreted. Therefore, animals at the top of the food chain tend to accumulate more. Further, such fish tend to live longer, allowing their mercury levels to increase over time. As a result, large, long-lived fish such as shark and swordfish have higher than average levels of mercury. In addition, certain waterways are known for high mercury levels, so the research team paid attention to where fish were caught.

Double the Risk of ALS

Researchers found that those who ate fish and seafood regularly and were in the top 25% for annual mercury exposure and had double the risk of ALS than those with lower mercury levels.

  • 61% of participants with ALS were in the top 25% for estimated mercury intake
  • Only 44% of participants without ALS were in the top 25%
  • Similarly, the toenail clipping results showed that higher mercury levels increased ALS risk

Study participants in the top 25% of mercury exposure, based on toenail clippings or fish/seafood intake, had twice the risk of developing ALS.

The study used a relatively small sample size, so larger studies are needed to confirm the results. Meanwhile, mercury is a known neurotoxin. Therefore, reducing your intake of this heavy metal from all sources, including fish and seafood, makes sense.