Julie Corliss

Make smart seafood choices to minimize mercury intake

Fish and shellfish are great sources of lean protein, and many types are rich in heart-healthy omega-3 fatty acids. But there’s a catch: some species of fish contain worrisome amounts of methylmercury, a toxin that’s especially dangerous to developing brains. That’s why women who are or could become pregnant and young children shouldn’t eat high-mercury fish such as swordfish, shark, king mackerel, and tilefish. A new study hints that eating too much—or the wrong kind—of salmon and tuna can also boost mercury levels.

The Dietary Guidelines for Americans advise us to eat eight ounces of seafood a week (12 ounces a week for women who are pregnant). That would deliver enough omega-3 fatty acids to help brain and nerve growth and protect the heart. But eight ounces is more than double the amount of fish the average American eats in a week.

The new study, published in the May issue of The American Journal of Clinical Nutrition, offers clues about how often and what types of seafood Americans eat, and how that affects mercury levels in the bloodstream. Researchers with the National Health and Nutrition Examination Surveys asked a nationwide sample of 10,673 adults what seafood they had eaten in the previous month. Shrimp was the most popular choice (46%), followed by tuna (34%), and salmon (27%). Only 2% said they had eaten high-mercury fish species.

Most of the participants (95%) had blood levels of mercury in the safe zone—under 5.8 micrograms per liter (μg/L). Not surprisingly, the more fish people ate, the higher the levels of mercury in their blood. Those who consumed swordfish, shark, and other high-mercury fish were the most likely to have blood levels of mercury above 5.8 μg/L. But some who ate only salmon or tuna also had high mercury levels.

Having a blood mercury level of 5.8 μg/L isn’t necessarily harmful for an adult, explains Dr. Emily Oken, an associate professor of population medicine at Harvard Medical School who has studied women’s fish consumption during pregnancy. “It’s very complicated to tease out the harmful effects of mercury because the primary source is from fish, and fish has nutrients that are beneficial to the brain and the heart, the same organs that mercury may harm,” she says.

Eat seafood, go for variety

Eating some fish is good. Eating lots of it might not be. Take, for example, the story of IMAX Corporation CEO Richard Gelfond. According to the Wall Street Journal, he ate sushi twice a day for two decades. After noticing numbness, balance, and coordination problems—all signs of mercury toxicity—he was found to have a blood mercury level of 72 μg/L. That’s 12 times higher than the safe level.

The health effects of blood mercury levels somewhat above the healthy range simply isn’t known. So what’s a fish aficionado—or just the average person hoping to follow a heart-healthy diet—supposed to do?

“As a physician, I recommend that people eat fish,” says Dr. Oken. Choose different types, and stay away from high-mercury species. If you eat canned tuna, look for chunk light, which is lower in mercury than other varieties. Don’t be overly concerned about salmon; the increased mercury level attributed to salmon consumption was quite small, and it’s possible that salmon eaters also ate more of the other high-mercury fish that contributed to the elevated level, says Dr. Oken. The table below, adapted from a study she led to promote healthy fish consumption in pregnant women, can help you make choices. It features low-mercury varieties and includes how much to eat to get suggested levels of omega-3 fatty acids.

If sustainability of fish populations is a concern for you, check out Seafood Watch from the Monterey Bay Aquarium. It aims to help consumers and businesses make choices for good health and healthy oceans.

Low-mercury seafood choices

There are many different ways to get the recommended weekly amount of omega-3 fatty acids. You can do it with a single meal of fish high in omega-3 fatty acids, or multiple meals of species with lesser amounts. (An expanded version of this table is available in the online Nutrition Journal.)

One 6-oz serving per week of OR two 6-oz servings per week of OR three 6-oz servings per week of
salmon (farm raised, wild caught, or canned)
whitefish/walleye
herring
anchovies (canned)
trout (farm raised)
Atlantic mackerel
sardines (canned)
trout (wild caught)
mussels
pollock
salt cod/bacalao
squid/calamari
ocean perch
flat fish
flounder
sole

 

Comments:

  1. Ceanix

    With the popularity of Omega 3 supplements, one also has to make wise choices regarding the brand of supplement they choose.

    Be aware of the source of the Omega 3 (referencing the low-mercury options presented in this article) and the extent of the testing procedures prior to bottling of the product.

  2. mukund lal

    hi this is too nice explanation. all the seafood like some fish are not healthy either for brain or body.
    thanks

  3. Scott

    I did a lot of research and reviewed many products on how to get the omegas from fish without the mercury intake. I found that krill oil is the new hot product. It’s supposedly has a lot less or no mercury and even is more potent than fish oil. I’ve been taking it for about a month and so far so good!

  4. Harvey Grove

    I found an omega 3 product that had a ifamiliar sweet odor to it, Eventually, I was able to recognize the odor and it was coconut. I had my pharmacist call the company and they admitted it was in the omega-3 pill. I asked why this was not on the label. The reply was, “it was labeled correctly and was in the section that stated…….and other ingredients.”

    Coconut oil is NOT GOOD for the heart yet it is in a product sold for heart health but not visible on the label. I purchased 2 bottles with the same control numbers but opened only one. I am sending them to FDA. Maybe they will make all products with this oil to be labeled more obviously.

  5. Kyla

    Fish has always been viewed as a healthier option where meat is concerned (along with chicken); however this article tells a different story. This is something not many people would take into consideration when choosing a diet of fish as the main protein. Although fish contains the omega-3 fatty acids needed in the body, the mercury levels are most likely to cause damage in the parts of the body originally helped by the fatty acids. A healthy consumption of fish would be an appropriate size, twice a week; however also fish low in mercury levels. This article is very helpful in that not many people know or understand this about this source of protein.

  6. valzon

    I agree, to reduce the intake of mercury in the body. Form methylmercury is a very dangerous can cause cancer. thank you, for sharing interesting information.

  7. www.clocaltoaction.com

    i liked it so much that you described normal/required mercury ratio for different people at different stages specially what you specified about expecting women.. thank you Julie. keep sharing :)

  8. Maya Mina

    According to U.S Geological Survey study the concentration of mercury in fish found in United States’ streams exceeds the norm. Low concentration of mercury may not harm yet numbers of statistics are too worrying. Mercury can harm unborn baby and affect young child’s nervous system. For adults too mercury can bring to serious problems like fertility, memory and vision problems, trouble with blood pressure; mercury can damage central nervous system and become a reason of psychological, neurological and immunological problems.

  9. To some of the other commenters: fish oil capsules (including cod liver) should be purified of mercury as well as other common contaminants. The label should indicate whether they’ve done this. To check the reputation of particular brands, Consumer Labs is a good source. It’s a subscription service though. Also, smoked salmon shouldn’t have an appreciably different quantity of mercury than fresh or frozen. In terms of farmed vs. wild, the mercury content of farmed will vary depending on where the fish are raised, but in probably every way wild fish is generally healthier to consume (whether or not sustainable in marine ecosystem ways.)

  10. Allen Meyer

    How do the guidelines vary as between wild-caught Atlantic vs. Pacific salmon, wild Alaska vs. other wild Pacific salmon? Lox or smoked wild salmon vs. fresh or farm-raised?

  11. BHARATHAN

    What about cod liver capsules? Do they have mercury?

    • AMEENAT

      Ialso want to know if cod liver fish oil is save.Where do we get the best and for people like us who like fish alot which fish is best and where do we get them in Malaysia

  12. BHARATHAN

    What about cod liver oil capsules? do they have mercury?

  13. Tim

    Being a fish fan, I found this to be really helpful. The tough thing, is measuring portion sizes, particularly if you’re at a restaurant, so it’s a little hard to gauge just how much you’re getting. Thoughts on how to manage mercury levels?

  14. Larry Bell

    What about clams in the half-shell, like Bluepoints?

    • Albert H. Harris

      Bluepoints are oysters, but, being stationary filter feeders, they would be subject to the chemical analysis of their beds.