Many people try to incorporate more fish into their diet as part of a healthy, balanced diet. However, most people try to avoid high mercury fish.
Fish is generally a very healthy cuisine. It’s known for being high in Omega-3 fatty acids, a vital micronutrient that your body cannot produce on its own. The omega-3 fatty acids aid in proper cell function, help reduce inflammation of blood vessels, improve brain health, and contribute to heart health.
Additionally, fish is a high-quality source of protein, and is rich in vitamins such as vitamin D and B12, as well as minerals such as iron, zinc, iodine, magnesium and potassium.
Diets high in fish such as the pescatarian diet and the mediterranean diet are generally very healthy diets, but it’s still important to be mindful of the high mercury fish out there.
Sometimes, fish can contain quite a high concentration of toxic chemicals due to the presence of pesticide residue, dioxins, and PCBs. Fish absorbs contaminants from many sources in their environment: the water they live in, the food they eat, and the sediments they come into contact with.
Of all the additional substances found in fish, mercury has gotten the most attention in recent years. The high levels of mercury that have been found in some fish have prompted some people to forgo fish altogether, while others have simply reduced the amount of fish they eat or have become more selective about where their fish comes from. Perhaps high mercury fish can be avoided, and that’s what we’ll review in this article.
Below, we’ll discuss what mercury is, what it can do to you, which fish are the worst in terms of mercury exposure. We’ll also review what you can do to reduce your risk of developing health problems due to mercury.
What is Mercury?
Mercury is a chemical compound that can be toxic to humans, leading to adverse health effects. It exists in nature that can be found in several forms. In its elemental form, mercury is a silver liquid commonly referred to as ‘quicksilver’. A mercury thermometer may be familiar to you. At one time, liquid mercury was used to make old fluorescent light bulbs, but that was discontinued when researchers looked into the possible health hazards of prolonged exposure to mercury.
Mercury reacts with other elements to form inorganic mercury. Inorganic mercury is a salt-like substance that attaches to air particles, which are then redistributed into the environment.
Once several complex chemical changes have taken place, mercury transforms into a toxic form of organic mercury called methylmercury. This is the most common type of mercury found in fish. The fish absorb it by breathing through their gills and by consuming other fish that have absorbed mercury. This leads to high mercury fish.
Why is Mercury Bad for You?
Mercury can be quite harmful to the human brain, kidneys, heart, lungs and immune system. In fact, in the 19th century, long-term exposure to mercury led to an epidemic of a condition known as erethism in hat makers. ‘Mad hatter disease’, as it came to be called, resulted from hat makers breathing in a chemical that contained mercury, which was used to smooth the felt that the hats were made of.
When mercury is inhaled, the particles cause damage to lung tissue. Additionally, breathing it in allows it to enter the bloodstream, where it is redistributed throughout the body, damaging other organs and systems.
Pregnant women need to be especially cautious of mercury exposure, as it can have devastating repercussions on the nervous system of a developing fetus, leading to cognitive impairment.
Research has shown that animals who rely on fish as one of their primary food sources have experienced many negative side effects such as delayed growth, reduced reproduction rates and death.
How Much Mercury is Too Much?
Mercury is a natural element, so it’s not possible to completely avoid your exposure to it, even if you avoid eating high mercury fish. There are degrees of exposure that should be avoided, however. It is recommended not to go over 0.045 mcg (microgram) of mercury per pound of body weight, per day. Mercury levels can be tested by examining blood and urine samples. Anything above 100 ng (nanograms)/mL in the blood is indicative of mercury poisoning.
For methylmercury, the most common type of mercury found in fish, the EPA has set limits of 0.01 mcg per kg of body weight as a safe level. Exceeding 5.8 mcg per litre of blood is considered unsafe.
High Mercury Fish: Which Fish Have the Highest Levels of Mercury?
Once fish have absorbed mercury through their gills, it becomes fully enmeshed in their flesh and fat. This means that once it’s there, there isn’t anything we can do to remove or reduce the amount of mercury in fish before we eat it.
We can, however, limit the amount of mercury we consume in fish by following the EPA guidelines of 0.045 mcg of mercury per pound of body weight, per day and capping our consumption of fish to 2 servings per week. Our bodies can’t make Omega-3s, and fish are an incredibly rich source of them, making them an essential part of a healthy diet.
Additionally, we can limit our mercury exposure by avoiding or strictly selecting certain kinds of fish, as some have higher levels than others.
Generally speaking, fish that grow larger and live longer have higher levels of mercury than smaller fish. This is because of their longer life span, which allows them more exposure time. Also, larger fish eat smaller ones, so they absorb more mercury when they consume it.
Fresh tuna hold some of the highest levels of mercury of all. Bluefin, big eye and albacore tuna contain 54-58 mcg of mercury per 4 ounces of cooked fish. Skipjack and yellowfin have slightly lower levels, between 31-49 mcg per 4 ounces. Meanwhile, canned white albacore tuna retains around 40 mcg. Light canned tuna has the lowest levels at only 13 mcg because usually smaller, younger tuna is used in canning.
Fish that contain high levels of mercury content include:
- Swordfish
- Canned white albacore tuna
- Shark
- King Mackerel
- Skipjack and yellowfin tuna
- Tilefish – at 219 mcg of mercury per 4 ounces of cooked fish, the tilefish is one of the highest mercury-containing fish out there.
- Northern Pike
- Orange Roughy
- Marlin
- Lobster
- Spanish Mackerel
- Bluefin, big eye and albacore tuna
- Barramundi
- Ling cod
- Ray
- Gemfish
Are Some Fish Lower in Mercury?
If you want the health benefits that come with eating fish, or if you just enjoy eating seafood, there are some species you can choose from that typically have lower mercury levels.
Fish or seafood lower in mercury include:
- Smaller fish such as anchovies and mackerel
- River-dwelling fish such as catfish
- Shellfish
Shellfish such as clams, crab, crawfish and oysters are lower in mercury than their fatty fish cousins. If you like a thicker, steak-like fish, choose from flounder, haddock, pollock, plaice, salmon or mullet.
Additionally, farmed fish tend to have slightly lower levels of mercury than fish caught in the wild because they are fed a diet of grains and soy, which is cheaper than fish meal and contains no ‘recycled’ mercury (that is, the mercury held in the flesh of smaller fish). Keep in mind, however, that farmed fish still live in the same waters as wild fish, so they will still absorb mercury through their gills.
What’s the Optimal Diet For You, Based on Your Genetics?
Some people are genetically better suited to a mediterranean diet, which typically involves plenty of fish.
Among the 500 different health reports offered to you by a CircleDNA test are some insightful genetic diet and nutrition reports, which help you determine the optimal diet plan for you, based on your DNA.
While fish is an important component of a healthy, balanced diet, it is just as important to be mindful of how much fish you’re consuming to negate the onset of any diseases or other health problems.
References
- Basic Information about Mercury (U.S. Environmental Protection Agency) https://www.epa.gov/mercury/basic-information-about-mercury#overview
- Mercury Reduces Avian Reproductive Success and Imposes Selection: An Experimental Study with Adult- or Lifetime-Exposure in Zebra Finch (Claire W. Varian-Ramos, John P. Swaddle & Daniel A. Cristol) https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0095674
