Mercury Poisoning: What You Should Know

Mercury Poisoning: What You Should Know

Sushi with chopsticks shot on white

By Kimberly Visioni, MS, RD, Contributing Blogger

I love seafood but I do think about how much mercury I’m really taking in when ordering fish or preparing it at home. The Food and Drug Administration (FDA) recommends pregnant women and young children to limit fish intake to no more than 12 ounces per week to avoid taking in too much mercury. I recently learned, however, that mercury is something we should all consider, pregnant or not! Last May, my friend Peter, asked for a comprehensive blood work-up during his annual physical. He wanted to get a detailed overview of his health status and he certainly did. His lab results indicated that his mercury levels were above normal. I later found out that he was eating sushi three times a week and his usual order was tuna, tuna and more tuna!


What Is Mercury?
Mercury is a naturally occurring element that is found in air, water and soil. When released into the air (often through industrial activities), it eventually settles into bodies of water such as streams, lakes and oceans. In water, microorganisms can transform mercury into methylmercury, which is absorbed by fish as they feed. This is the form that we hear about most of the time because we’re exposed to it when we eat contaminated fish and shellfish. Almost all fish contain trace levels of methylmercury in their tissues. However, the oldest and largest fish will have the highest levels, simply due to the fact that they’ve either been around the longest or they’ve eaten more fish, both of which put them at the top of the charts for mercury absorption.


How Do You Get Mercury Poisoning?
Long-term exposure to high levels of methylmercury can lead to mercury poisoning, which may cause damage to the nervous system. Elevated levels can affect anyone but the most sensitive populations include women who are pregnant or nursing and young children. Methylmercury can accumulate in the blood and tissues of a growing fetus or in young children, which can disrupt their brain and nervous system development. This is why the FDA and Environmental Protection Agency (EPA) recommend that women who may become pregnant, pregnant women, nursing mothers and young children do not eat shark, swordfish, king mackerel, or tilefish (remember, the large fish at the top of the food chain). White (Albacore) tuna has more mercury than canned light tuna so they also advise the same population to limit albacore tuna to 6 ounces a week.

Okay, so you’re thinking no problem, I’m not pregnant, I’m not breastfeeding and shark isn’t exactly on my weekly grocery list. But take a look at the FDA’s list of fish and the amount of mercury in each. Although fresh tuna is not on the top four fish to avoid, it has more mercury than most other fish. Plus, tuna seems to be a popular menu item at most restaurants. This might be how my pal Peter got into trouble. He said he was often working late last spring and it became easy (and delicious) to simply order the same dinner from his local sushi restaurant.

His whole blood mercury level was 33 ng/mL (nanograms per milliliter) in May. Normal levels are usually less than 10 ng/mL. Most people have trace amounts of methylmercury in their bodies but they usually don’t pose any health concerns. Even at elevated levels, you may not experience any symptoms or health issues, like Peter. Given that he was asymptomatic, his physician advised him to lower his levels by removing the source (tuna) from his diet. He was retested in August and his levels dropped to 19 ng/mL. Based on the extent of mercury toxicity and symptoms, some people may need chelation therapy, which uses chelators to bind to mercury and help remove it from the body through urination.


Should You Still Eat Fish?
Of course! Fish is an important part of a well-balanced, healthy diet. It’s a great source of protein, minerals like iron and zinc, as well as omega-3 fatty acids, which are good for both heart and brain health. Plus, fish is low in calories and saturated fat. In fact, the FDA recommends eating 8 to 12 ounces a week of a variety of fish and shellfish that are lower in mercury (one serving is about 4 ounces). These include shrimp, salmon, canned light tuna, tilapia, pollock and catfish. Mercury consumption is on the FDA’s radar and they don’t allow fish to be sold for consumption if it has mercury levels over 1ppm (1 part methylmercury per million parts of fish). But, if you’re like Peter and you like eating fish and you’re still concerned with what you’re eating, The Natural Resources Defense Council has a great guide for choosing fish based on mercury levels.

Peter’s mercury level hasn’t led to any serious health issues but let’s just say it gave him some “food for thought”. I know you’ve heard it before, but when it comes to eating seafood, like everything else, variety and moderation is always the way to go!


Kimberly Visioni, MS, RD is a registered dietitian with a master’s degree in Nutrition and Education from Teachers College, Columbia University. Prior to becoming a dietitian, Kimberly worked in the fashion industry for over 10 years. She is now starting a private practice that will provide clients with the knowledge and skills necessary to navigate the multitude of food options and situations they are exposed to on a daily basis. Kimberly knows that inspiring and empowering her clients with knowledge about diet and exercise will help them achieve their best self. Growing up as a competitive swimmer has been the catalyst to Kimberly’s athletic lifestyle. She enjoys taking fitness classes, training for triathlons, distance running and of course cooking up healthy recipes for friends and family.  You can find her via LinkedIn

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1 Comment
  • Bonnie Modugno
    Posted at 09:54h, 22 February Reply

    Not all mercury is “naturally occurring”. Do you know what percentage is derived from industry and other sources of pollution?

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