Does Eating Fish Really Increase Your Mercury Levels?

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One thing everyone seems to agree on is that eating fish is healthy, but many also say that because of current fish mercury levels, eating fish can increase the mercury levels in your own body and that this can cause many harmful health problems. Eat fish, just don’t eat too much—that’s the plug.

There are infographics online that list fish species that have the least amount of mercury contamination (e.g., catfish, oysters, and tilapia) and the highest amount of mercury contamination (e.g., swordfish, orange roughy, and tuna). You can print wallet cards to carry with you so you’ll always have how much fish you should eat, what type, and how often right at your fingertips. There are even apps you can pull up right on your smartphone to measure mercury levels in your sushi. But is all this really necessary? Is eating a little extra fish every now and then really all that bad?

The Fish Mercury Connection

The mere mention of mercury takes many of us back to middle-school science class. The mercury on the periodic table (Hg, number 80) is the same mercury that makes its way into our lakes, rivers, and oceans. Mercury is an element found naturally in the environment, and both natural sources, such as volcanic eruptions, and unnatural sources, such as industrial emissions and intentional dumping, are responsible for its presence in our bodies of water.

Once in the water, a complex chemical process converts mercury to methylmercury, the mercury found in our fish, and there are many theories as to how this happens. Scientists are even looking at the possibility that methylmercury is generated by a specific layer in the ocean itself. However it happens, our fish consume it, and we, in turn, consume our fish.

This leads us back to our presenting question: does eating fish really increase your mercury levels? If so, is this a bad thing?

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Mercury Study on the Brain

A recent study looked at whether eating fish increased mercury levels, and if so, whether or not it resulted in a brain pathology, or disease, such as Alzheimer’s disease, Lewy bodies, and cerebral infarctions. The study looked at 554 deceased elderly participants with a mean age of 89.9. Via a questionnaire, seafood consumption was first measured about 4.5 years prior to death. Researchers autopsied 286 brains, and they found that the brains did indeed have mercury levels consistent with the amount of seafood consumed. For example, people who ate more fish had more mercury in the brain. The researchers expected to find that this, of course, meant that these moderate-to-high fish-consumption people had more brain problems.

However, the surprise finding of the study was that people who consumed moderate amounts of seafood, in fact, showed less Alzheimer’s disease pathology! So while this study answers our question—yes, eating fish really does increase our mercury levels—there was no association between those higher levels of mercury and brain problems. In fact it went the other way, showing less potential for Alzheimer’s disease.

The upshot? While you wouldn’t want to bet the bank on the results of one study, the results are likely important. The health benefits of fish are undeniable, and the concern for mercury’s impact on our environment and fish supply isn’t going to subside anytime soon. Everything in moderation and that includes eating fish mercury and all. So don’t sweat that extra tuna steak or sushi roll and there’s likely no need to buy that smartphone app!

Chris Centeno, MD is a specialist in regenerative medicine and the new field of Interventional Orthopedics. Centeno pioneered orthopedic stem cell procedures in 2005 and is responsible for a large amount of the published research on stem cell use for orthopedic applications. View Profile

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Category: Diet/Nutrition
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