Tuna is a saltwater fish eaten all over the world.
It’s incredibly nutritious and a great source of protein, omega-3 fatty acids and B vitamins. However, it can contain high levels of mercury, a toxic heavy metal.
Natural processes — such as volcanic eruptions — as well as industrial activity — such as coal burning — emit mercury into the atmosphere or directly into the ocean, at which point it begins to build up in marine life.
Consuming too much mercury is linked to serious health issues, raising concerns about regular intake of tuna.
This article reviews mercury in tuna and tells you whether it’s safe to eat this fish.
This is because tuna feed on smaller fish which are already contaminated with varying amounts of mercury. Since mercury is not easily excreted, it builds up in the tissues of tuna over time (, ).
Levels in Different Species
Levels of mercury in fish are measured either in parts per million (ppm) or micrograms (mcg). Here are some common tuna species and their mercury concentrations (1):
|Species||Mercury in ppm||Mercury (in mcg) per 3 ounces (85 grams)|
|Light tuna (canned)||0.126||10.71|
|Skipjack tuna (fresh or frozen)||0.144||12.24|
|Albacore tuna (canned)||0.350||29.75|
|Yellowfin tuna (fresh or frozen)||0.354||30.09|
|Albacore tuna (fresh or frozen)||0.358||30.43|
|Bigeye tuna (fresh or frozen)||0.689||58.57|
Reference Doses and Safe Levels
The US Environmental Protection Agency (EPA) states that 0.045 mcg of mercury per pound (0.1 mcg per kg) of body weight per day is the maximum safe dose of mercury. This amount is known as a reference dose (4).
Your daily reference dose for mercury depends on your body weight. Multiplying that number by seven gives you your weekly mercury limit.
Here are some examples of reference doses based on different body weights:
|Body weight||Reference dose per day (in mcg)||Reference dose per week (in mcg)|
|100 pounds (45 kg)||4.5||31.5|
|125 pounds (57 kg)||5.7||39.9|
|150 pounds (68 kg)||6.8||47.6|
|175 pounds (80 kg)||8.0||56.0|
|200 pounds (91 kg)||9.1||63.7|
Since some tuna species are very high in mercury, a single 3-ounce (85-gram) serving may have a mercury concentration that equals or exceeds a person’s weekly reference dose.
Summary Tuna is high in mercury compared to other fish. A single serving of some types of tuna may surpass the maximum amount of mercury that you can safely consume per week.
Mercury in tuna is a health concern because of the risks associated with mercury exposure.
Just as mercury builds up in fish tissues over time, it can also accumulate in your body. To assess how much mercury is in your body, a doctor can test mercury concentrations in your hair and blood.
High levels of mercury exposure can lead to brain cell death and result in impaired fine motor skills, memory and focus ().
In one study in 129 adults, those with the highest concentrations of mercury performed significantly worse on fine motor, logic and memory tests than those who had lower levels of mercury ().
Mercury exposure may also lead to anxiety and depression.
A study in adults exposed to mercury at work found that they experienced significantly more depression and anxiety symptoms and were slower at processing information than control participants ().
Finally, mercury buildup is linked to a higher risk of heart disease. This may be due to mercury’s role in fat oxidation, a process that can lead to this illness ().
In a study in over 1,800 men, those who ate the most fish and had the highest mercury concentrations were two times likelier to die from heart attacks and heart disease ().
However, other research suggests that high mercury exposure is not associated with an increased risk of heart disease and that the benefits of eating fish for heart health may outweigh the possible risks of ingesting mercury ().
Summary Mercury is a heavy metal that can cause adverse health effects. High concentrations of mercury in humans may trigger brain issues, poor mental health and heart disease.
Tuna is incredibly nutritious and packed with protein, healthy fats and vitamins — but it should not be consumed every day.
However, research indicates that regularly eating fish with a mercury concentration greater than 0.3 ppm may increase blood levels of mercury and spur health issues. Most species of tuna exceed this amount (1, ).
Therefore, most adults should eat tuna in moderation and consider choosing other fish that is relatively low in mercury.
When buying tuna, opt for skipjack or canned light varieties, which do not harbor as much mercury as albacore or bigeye.
Try to avoid eating albacore or yellowfin tuna more than once per week. Refrain from bigeye tuna as much as possible (10).
Summary Skipjack and canned light tuna, which are relatively low in mercury, can be eaten as part of a healthy diet. However, albacore, yellowfin and bigeye tuna are high in mercury and should be limited or avoided.
Certain populations are especially susceptible to mercury and should limit or completely abstain from tuna.
These include infants, young children and women who are pregnant, breastfeeding or planning to become pregnant.
Mercury exposure can impact embryo development and may lead to brain and developmental issues.
In a study in 135 women and their infants, each additional ppm of mercury consumed by pregnant women was tied to a decrease of over seven points on their infants’ brain function test scores ().
However, the study noted that low-mercury fish was associated with better brain scores ().
Health authorities currently advise that children, pregnant women and breastfeeding mothers should limit intake of tuna and other high-mercury fish, instead aiming for 2–3 servings of low-mercury fish per week (4, 10).
Summary Infants, children and women who are pregnant, breastfeeding or trying to conceive should limit or avoid tuna. However, they may benefit from eating low-mercury fish.
Mercury exposure is linked to health issues including poor brain function, anxiety, depression, heart disease and impaired infant development.
Though tuna is very nutritious, it’s also high in mercury compared to most other fish.
Therefore, it should be eaten in moderation — not every day.
You can eat skipjack and light canned tuna alongside other low-mercury fish a few times each week, but should limit or avoid albacore, yellowfin and bigeye tuna.