The most common type of mercury poisoning comes from eating fish, so it is no wonder that many people in the United States do not eat the recommended amount of fish and seafood because they are worried about mercury in fish. High levels of mercury can have a devastating effect on the brain, heart, kidneys, lungs, and immune system.
The American Heart Association and the 2015-2020 Dietary Guidelines for Americans recommend eating fish at least twice weekly and at least 8 ounces total—but only 1 in 10 Americans follow these guidelines. The average person eats 3.5 ounces of fish per week, and the number drops to an average of 2 ounces during pregnancy.
Feeling worried is natural when you read about high levels of mercury in fish, but you do not want to miss out on the health benefits of eating fish and seafood. They are great sources of protein and omega-3 fatty acids. So, should you be worried about mercury poisoning from fish?
The Latest Research on Mercury Poisoning from Fish
If you have been cutting fish out of your diet because you are scared of mercury poisoning, the latest research might make you change your mind.
Mercury is an element that occurs naturally in the air. Unfortunately, human industrial activity, such as electricity produced by coal and the incineration of waste, releases elemental mercury, thereby raising the levels of mercury in the air.
From the air, mercury gets into oceans, rivers, and lakes, where some microorganisms transform it into methylmercury—this is how mercury ends up in fish and shellfish. The highest concentrations of methylmercury are generally found in large predators because they are at the top of the food chain and have a longer life. Fish also contains another element, selenium, which might hold the key to protecting the brain from mercury.
Selenium is an antioxidant mineral that plays a key role in brain health. According to Nicholas Ralston, Ph.D., a research scientist at the University of North Dakota’s Energy and Environmental Research Center, the confusion about mercury and seafood comes from conflicting results from large studies on the effects of mercury on childhood brain development. A study from the Faroe Islands and another study from New Zealand found low incidences of harm from mercury exposure from seafood. Ralston spoke at the annual meeting of the Academy of Nutrition and Dietetics in Boston in October 2016 and said that when researchers investigated further, they found the selenium link. Selenium acts as a mercury magnet—it attracts toxic substances and reduces their damage.
Fish does not just contain mercury—it is also a great source of selenium. Flounder, tuna, and wild Pacific salmon (including Chinook, Sockeye, and Coho) have much more selenium than they do mercury. Tilefish, king mackerel, swordfish, and shark, instead, have more mercury and less selenium. You’ll want to consume fish sources that are not processed to make sure you get more selenium than mercury.
Check this chart to see the levels of selenium vs. mercury in ocean fish.
The Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) recommend that pregnant and breastfeeding women eat 8 to 12 ounces of lower mercury fish per week to foster fetal growth and child development, as well as the mother’s health.
Symptoms of Mercury Poisoning
The first signs of mercury poisoning include:
- Anxiety and edginess
- Mood disturbances and depression
- Memory lags
As the amount of mercury in the body goes up, additional symptoms emerge, such as:
- Muscle weakness
- Vomiting and nausea
- Metal taste in the mouth
- Lack of coordination
- Loss of feeling in the hands, face, or other areas
- Changes in vision, hearing, or speech
- Shortness of breath
- Inability to walk or stand up straight
Which Fish Have the Most Mercury?
Large fish contain more mercury because they usually live longer and have more time to absorb higher levels of mercury in their bodies. The EPA recommends that you check local advisories to know the mercury content of fish in your area.
The list below shows general mercury levels of many common types of fish and how much of each type to eat, according to the National Resource Defense Council. You can also check the FDA list. The EPA, NRDC, and FDA might show slightly different results for the specific type of fish.
Low Mercury Fish
Eat two to three servings a week of the following fish. Experts advise pregnant and small children eat no more than 12 ounces or two servings.
Fish with Modest Levels of Mercury
Eat six servings or fewer per month. We recommend that pregnant women and small children do not eat these, as high levels of mercury can damage an unborn baby or young child's developing nervous system.
|Perch (freshwater)||Mahi Mahi|
High Mercury Fish
Eat three servings or less per month. We recommend that pregnant women, nursing mothers, and small children do not eat these.
- Sea Bass
- Perch (ocean)
- Tuna (canned albacore, yellowfin)
Fish with the Highest Mercury
The FDA recommends that you avoid:
- King mackerel
- Tuna (bigeye, ahi)
- Orange roughy
How Much Mercury Is Too Much?
Scientists do not know the specific level of mercury that leads to harmful effects. Swedish biologists discovered that a small portion of the population carries a genetic mutation that makes their cells absorb mercury much longer, and it’s postulated that those people may be at higher risk.
The EPA recommends consuming a daily maximum of 0.1 micrograms of mercury for each kilogram of your body weight. That means a 176-pound adult (the national average) should eat no more than 8 micrograms of mercury each day. In practical terms, it depends on the mercury concentration you eat, but to give you an idea, the average adult could eat 13 ounces of fresh salmon per day without risks. Just 0.14 ounces of swordfish, instead, would put you over the limit.
Keep in mind that calculations made by the FDA, EPA, and NRDC are constantly under revision because mercury concentrations are rapidly changing. The amount of fish you’ll be able to consume while staying within the limits will decrease over time.
The damage from mercury toxicity is often permanent. Call the Poison Control Center at 800-222-1222 if you think you or a loved one might have mercury poisoning.