Tuna is a rich source of omega-3 fatty acids, high-quality protein, essential vitamins, and important trace minerals, making it a valuable addition to a balanced, nutrient-dense diet.
Unfortunately, large predatory fish species, including tuna, often contain high levels of mercury, an environmental heavy metal that can have numerous health consequences.
Find out which types of tuna have the highest mercury levels and learn how to enjoy this oily fish as part of a nutritious diet while keeping heavy metal exposure to a minimum.
What is mercury?
Mercury is a naturally occurring heavy metal found in air, water, and soil. Human activity, such as mining, coal burning, and industrial processes, has significantly increased its presence in the environment.
In high amounts, mercury acts as a neurotoxin, potentially affecting the brain and nervous system. Long-term or high-level exposure can result in mercury toxicity, which may lead to serious health effects.
Common symptoms of mercury toxicity include:
- Tremors
- Headaches
- Nausea
- Poor coordination
- Peripheral neuropathy
- Skin rashes
- Poor memory
- Trouble speaking
- Vision loss
- Muscle weakness
- Twitches
- Insomnia
- High blood pressure
- Mood swings and anxiety
- Fatigue
Mercury, especially in its organic methylmercury form, has a high affinity for fatty acids and accumulates in lipid-rich tissues, including the brain.
This makes it particularly dangerous for the central nervous system, where it can interfere with neuronal function, development, and communication.
Why do fish contain mercury
Most fish contain mercury due to widespread environmental contamination.
Mercury that’s released into the atmosphere eventually settles into oceans, rivers, and lakes, where microorganisms convert it into methylmercury, a highly toxic form that accumulates in aquatic life.
As smaller organisms are eaten by larger ones, methylmercury moves up the food chain, leading to significantly higher concentrations in large predatory fish such as tuna, shark, and swordfish.
While mercury contamination is a global issue, areas near coal-burning power plants, gold mining, or industrial pollution typically show higher mercury levels in local fish than more remote or protected ecosystems.
Watch the video below to learn more about mercury contamination in tuna fish.
How much mercury is in tuna?
To minimize mercury exposure, it’s important to choose tuna species with lower mercury concentrations.
Because mercury toxicity is dose-dependent, the risk increases with the frequency and quantity of tuna consumption, and young children, due to their low body weight, should consume high-mercury fish no more than once per month.
Mercury exposure is also of particular concern during pregnancy, as the developing fetus is highly sensitive to heavy metals. For this reason, pregnant women are advised to limit their intake of high-mercury fish, including certain types of tuna.
Bigeye tuna has been found to contain mercury levels as high as 1.816 parts per million (ppm), according to data published by the Food and Drug Administration (FDA).1
Ahi tuna contains nearly three times the amount of methylmercury found in canned light or skipjack tuna. Albacore, as well as yellowfin and bigeye tuna varieties, generally appear to contain the highest mercury levels.
Research published in StatPearls notes that mercury is eliminated from the body slowly, which contributes to its potential for accumulation over time and underscores the importance of monitoring long-term dietary intake.2
Interestingly, selenium helps lower the risk of mercury accumulation because it binds to mercury and forms a biologically inert compound that the body can detoxify and excrete more easily.
This explains why selenium-rich fish species such as sardines, wild-caught salmon, and Atlantic mackerel are often considered safer seafood choices despite also containing trace amounts of mercury.
What is the healthiest tuna?
To enjoy the nutritional benefits of tuna while minimizing mercury exposure, opt for species known to contain lower levels of this neurotoxic heavy metal.
Skipjack tuna is among the lowest in mercury, and canned light tuna, often labeled as chunk light, is generally safer than albacore or yellowfin varieties.
The geographic origin of the fish can also influence mercury levels. Tuna caught in the Mediterranean region has been shown to contain up to five times more mercury than tuna from other regions, due to factors such as industrial emissions and volcanic activity.
“Mercury accumulation is most pronounced in large, long-lived predatory fish, and species such as tuna, swordfish, shark, and grouper typically contain the highest mercury concentrations,” explains Dr. Berg. “In contrast, smaller fish and shellfish accumulate far less mercury over their lifespan.”
Incorporating lower-mercury alternatives, such as canned sockeye or pink Alaskan salmon, wild-caught sardines, and other small oily fish, can provide essential nutrients while minimizing mercury exposure.
Some of the best low-mercury fish and seafood options include:
- Anchovies
- Catfish
- Clams
- Crabs
- Crawfish
- Flounder
- Haddock
- Herring
- Oysters
- Sardines
- Scallops
- Squid
- Trout
- Tilapia
Key takeaways
It’s challenging to completely avoid mercury due to its widespread presence in the environment.
However, limiting high-mercury fish such as bigeye and yellowfin tuna, while incorporating lower-mercury options like skipjack or sardines, can help limit exposure to this toxic heavy metal.
Including fish naturally rich in selenium, such as sardines, wild-caught salmon, and Atlantic mackerel, may also be beneficial, as selenium can bind to mercury and support the body’s detoxification processes.
FAQ
1. How much mercury is in tuna?
Mercury levels in tuna vary by species. For example, bigeye tuna can contain up to 1.816 parts per million (ppm), while skipjack and canned light tuna generally have significantly lower levels, often below 0.13 ppm.
2. Is tuna actually high in mercury?
Yes, all tuna contains methylmercury, though levels vary by species. Bigeye tuna tends to have the highest concentrations, making it one of the most mercury-contaminated types of tuna.
3. How much tuna can I eat per week?
Tuna species with lower mercury levels can be consumed 2 to 3 times per week. However, pregnant women, nursing mothers, and children should limit their intake to no more than once a month.
4. How can I reduce mercury in tuna?
To reduce mercury intake from tuna, choose species with lower mercury levels, such as skipjack or light canned tuna, and limit consumption of larger, predatory fish like bigeye or yellowfin.
Additionally, incorporating selenium-rich fish such as sardines, wild-caught salmon, and Atlantic mackerel may help mitigate mercury’s potential harmful effects in the body.
5. Which type of tuna has the most mercury?
Bigeye tuna contains the highest levels of mercury, followed by albacore tuna, which can have up to twice the mercury concentration found in skipjack or canned light tuna.
6. Which type of tuna has the least mercury?
Skipjack tuna, commonly found in canned light tuna and chunk light tuna, contains the least amount of mercury compared to other tuna species and is a better choice for reducing mercury intake.
7. Can I have canned tuna on keto?
Yes, you can eat tuna on keto. Canned tuna is a great source of protein and healthy fats for a ketogenic diet. To minimize mercury exposure, opt for canned light tuna or skipjack varieties.
8. Does canned tuna have more mercury?
Canned tuna doesn’t have more mercury than fresh tuna. In fact, canned light varieties actually contain significantly less mercury than fresh ahi tuna.
9. How much mercury is toxic?
The toxic threshold for mercury varies depending on individual factors such as body weight and overall health, but levels exceeding 5.8 micrograms per liter of blood may pose health risks. Chronic exposure to even lower levels can accumulate over time, leading to mercury poisoning.
10. Why do fish contain mercury?
Mercury is a naturally occurring element, but its levels have significantly increased due to industrial activities and mining.
As mercury settles in bodies of water like rivers, streams, and oceans, fish absorb it from their environment. Larger, longer-living fish that consume other fish tend to accumulate higher levels of mercury due to both environmental and food chain exposure.
Sources
- https://www.fda.gov/food/metals-and-your-food/mercury-levels-commercial-fish-and-shellfish-1990-2012 ?
- https://www.ncbi.nlm.nih.gov/books/NBK499935/ ?
