Is Mercury in Fish Harmful?

You may have already heard that omega-3 fatty acids are anti-inflammatory and effective in the prevention or reversal of many health problems.  Most people don’t get nearly enough, so doctors recommend high quality fish oil supplements.

There’s some debate about whether fish oil supplements are beneficial.  But there is almost unanimous agreement that eating fish is beneficial.

Sounds simple enough, right?  I thought so too until I went to buy some fish.  Right away I noticed there are many kinds of fish to choose from and I had heard that some should be avoided because of high mercury content.

Then there were the labels with terms like “Wild Caught”, “Farm Raised”, “Ocean Farmed”, “Sustainably Farmed” and “Vegetarian Feed”.

Since fish can be one of the pricier proteins, it would be nice to know you’re spending the food budget on something that won’t poison you.

That’s why I put together this quick primer to give you the facts on fish.

The two main issues with fish are:

1. Farm raised fish tend to be fed GMO feed.  I won’t spend much time on GMO in this post, but that’s why health professionals now recommend going with wild caught fish only.
2. Mercury levels can be a problem no matter how the fish was caught.

Here’s why you should care about mercury levels in fish and what fish you should avoid to keep mercury levels to a minimum.

Mercury is toxic

According to to the EPA, symptoms from varying levels of mercury accumulation in the body include:

• impaired neurological development
• impaired memory
• impaired attention
• impaired language
• impaired fine motor skills
• impaired peripheral vision
• disturbances in sensations (“pins and needles” feelings, usually in the hands, feet, and around the mouth)
• impaired speech
• impaired hearing
• muscle weakness
• feeling tired
• muscle pain
• twitches
• insomnia
• digestive problems
• food allergies
• depression
• anxiety
• increased cancer tumor size (not tested in humans)
• tremors
• emotional changes (e.g., mood swings, irritability, nervousness, excessive shyness)
• headaches
• changes in nerve responses
• performance deficits on tests of cognitive function
• kidney effects
• respiratory failure
• and death

Dr. Mark Hyman, health advisor to notables like Bill and Hillary Clinton, knows first-hand about mercury toxicity.  After growing up on tuna sandwiches and living for awhile in Beijing, he found himself facing many symptoms of mercury poisoning.  He also learned how to cure himself.

Where are we exposed to Mercury?

Some common places include:

• vapors in the air from coal burning plants
• ingestion via drinking water
• fish – #1 way humans are exposed
• dental fillings where amalgam is used (FDA considers dental amalgam fillings safe for adults and children ages 6 and above.  Interestingly, though stated to be safe in you mouth, it is illegal to throw a removed filling in the garbage.)
• vaccines
• occupational and home exposures including florescent light bulbs, thermostats, batteries, red tattoo dye, skin lightening creams, & contact lens cleaner

Mercury accumulates in your tissue over time

According to the EPA:

Bioaccumulation refers to the build-up or steadily increasing concentration of a chemical in organs or tissues in the body.  Mercury from dental amalgam and other sources (e.g., fish) is bioaccumulative. Studies of healthy subjects … have shown that mercury from exposure to mercury vapor bioaccumulates in certain tissues of the body including kidneys and brain.

Since we’re talking primarily about fish, larger fish have higher concentrations of mercury because they eat smaller fish and accumulate all the mercury that was absorbed by the smaller fish.

This is crucial.  Selenium counteracts the adverse effects of mercury exposure.  To read how this works, see this article by Chris Kresser.  Chris says, “Mercury is only harmful because it binds to selenium and prevents it from performing its vital roles in the brain. As long as you are eating fish that contains more selenium than mercury, the amount of selenium in the body will always be in plentiful excess of mercury. That means that these essential selenoenzymes are never inhibited to a meaningful degree. Fortunately, the vast majority of fish most people consume have more selenium than mercury. The exceptions are pilot whale, shark, tilefish, king mackerel and swordfish.”

So now we know why it’s a good idea to avoid mercury with a higher ratio than selenium.  Let’s take a look at the measured concentration of this dangerous metal in various kinds of commercial fish.

Fish with low mercury – Enjoy these fish!

An easy general rule to remember:  If it fits in your pan, it’s probably okay.

I looked up average measured mercury levels in commercial fish in the FDA list of Mercury Levels in Commercial Fish and Shellfish (1990-2010)  Here’s the list of those with levels considered safe for pregnant women (concentrations below 0.09 parts per million).  But keep in mind as long as they contain sufficient selenium, any mercury would be counteracted.

• Anchovies
• Butterfish
• Croaker (Atlantic)
• Flatfish (Flounder, Plaice & Pacific Sole)
• Flounder
• Haddock (Atlantic)
• Hake
• Herring
• Mackerel (N. Atlantic, Pacific Chub)
• Mullet
• Perch (Ocean)
• Plaice
• Pollock
• Salmon (Canned)
• Salmon (Fresh)
• Sardine
• Shad (American)
• Sole (Pacific)
• Tilapia
• Trout (Freshwater)
• Whitefish
• Whiting

Fish with moderate mercury but also sufficient selenium

According to the NRDC Consumer Seafood Buying Guide, these sea creatures have moderate mercury concentrations (between 0.09 and 0.29 ppm).

• Bass (Striped, Black)
• Carp
• Cod (Alaskan)
• Croaker (White Pacific)
• Halibut (Atlantic)
• Halibut (Pacific)
• Jacksmelt (Silverside)
• Lobster
• Mahi Mahi
• Monkfish
• Perch (Freshwater)
• Sablefish
• Skate
• Snapper
• Tuna (Canned chunk light)
• Tuna (Skipjack)
• Weakfish (Sea Trout)

High Mercury but also sufficient selenium

High concentrations of mercury were considered to be between 0.3 to 0.49 ppm.  These should be limited to 3 servings or less per month.

• Bluefish
• Grouper
• Mackerel (Spanish, Gulf)
• Sea Bass (Chilean)
• Tuna (Canned Albacore)
• Tuna (Yellowfin)

Highest Mercury but low selenium – Avoid!

The highest mercury levels of all fish were more than .5 ppm and this is the list to avoid eating.

• Mackerel (King)
• Pilot Whale
• Shark
• Swordfish
• Tilefish

When to Buy and How to Store Fish

Dr. Josh Axe offers these tips

When you’re buying fish be sure that it is fresh, doesn’t smell ‘fishy,’ and know that it has been properly stored (on ice and in refrigeration.) If the fish is older than one or two days don’t buy it and move on to a fresher choice.

If for some reason you don’t eat the fish you buy be sure to cook the fresh fish and properly freeze it within two days of purchase at the most. Also, remember if you freeze the fish, don’t keep it for more than three months. A good rule of thumb again, is the smell. If it smells fishy then don’t eat it. Same goes for if the fish feels slimy. Don’t take the risk.

Please subscribe to my email list and I will let you know whenever I publish new content to help you become the best and healthiest version of you.

Thanks for reading!

Jeff

Resources:

FDA list of Mercury Levels in Commercial Fish and Shellfish (1090-2010)

EPA About Dental Amalgam Fillings

The NRDC Consumer Guide to Mercury in Fish

Dr. Mark Hyman – The Impact of Mercury on Human Health and the Environment

If you wanna geek out for extra credit, this video shows actual video of what mercury does to neurons in the brain.