Eating Fish With Higher Mercury May Increase Risk of ALS

Possible association found between high mercury exposure and ALS.

Consuming seafood with high levels of mercury may increase the risk of developing amyotrophic lateral sclerosis (ALS), a preliminary study found.

“For most people, eating fish is part of a healthy diet,” said study author Elijah Stommel, MD, PhD. “But questions remain about the possible impact of mercury in fish.”

ALS is a neurodegenerative disease that affects the nerve cells in the brain and spinal cord. Muscles begin to atrophy leading to the eventual inability to walk, speak, swallow, and breathe.

In total, 518 individuals were surveyed on the amount of fish and seafood they consumed, of whom, 294 had ALS and 224 did not. Participants were asked to report the types of fish they ate and whether they were purchased from stores or caught while fishing.

The investigators estimated the annual exposure to mercury by obtaining the average mercury levels in the types of fish and the frequency the participants reported eating them. Additionally, levels of mercury in toenail samples of ALS patients were measured and compared with levels individuals without ALS.

The results of the study showed that those who regularly at fish and seafood—–those in the top 25% for estimated annual mercury intake––had double the risk for ALS compared with individuals with lower levels.

A total of 61% of ALS patients were in the top 25% of estimated mercury intake, compared with 44% of individuals without the disease.

The investigators also found that higher mercury levels measured in toenail clippings were associated with an increased risk of ALS. Participants in the top 25% of mercury levels were at a 2-fold higher risk of ALS.

The authors noted that the findings must be replicated in additional studies.

The FDA recommends that women of childbearing age and children eat 2 to 3 weekly meals of species with low mercury, such as salmon or sardines, but are high in nutrients. The agency also recommends avoiding fish with the highest mercury levels, such as swordfish and shark.

The authors stressed that the study does not negate the multiple health benefits fish provides. However, the findings do suggest that individuals take into consideration consuming fish with lower mercury content and to avoid those caught in waters where mercury contamination is well-known.

The findings will be presented at the 68th American Academy of Neurology annual meeting in Boston, Mass., April 22 to 28, 2017.