Tuna is a saltwater fish that is
widely consumed around the world.
It's high in protein, omega-3 fatty acids, and B vitamins and is
relatively healthy. It may, however, contain significant quantities of mercury,
a dangerous heavy metal.
Mercury is released into the atmosphere or directly into the ocean
by natural processes such as volcanic eruptions and industrial activity such as
coal burning, where it builds in marine life.
Too much mercury in the diet has been linked to significant health
problems, prompting concerns about regular tuna intake.
This article examines the mercury levels of tuna and evaluates if
it is safe to consume this fish.
How Contaminated Is It?
Other popular seafood foods, such as salmon, oysters, lobster,
scallops, and tilapia, have more mercury than tuna.
Because tuna feed on smaller fish already contaminated with
varying levels of mercury, this is the case. Because mercury is difficult to
remove, it builds in tuna tissues over time.
Levels in Different Species
Mercury levels in fish are measured in parts per million (ppm) or micrograms (mcg). The following are some common tuna species and their mercury levels:
| 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 |
Safe Levels and Reference Doses
According to the US Environmental Protection Agency (EPA), the
maximum safe amount of mercury is 0.045 mcg per pound (0.1 mcg per kg) of body
weight per day. This is known as a reference dose.
Your body weight calculates your daily mercury reference dose. The
weekly mercury limit is calculated by multiplying that number by seven.
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 |
Because some tuna species are high in mercury, a single 3-ounce
(85-gram) serving could contain enough mercury to equal or exceed a person's
weekly reference dose.
Dangers of Mercury Exposure
Because of the risks associated with mercury exposure, mercury in
tuna is a health concern.
Mercury can build up in your body in the same way it does in fish
tissues over time. A doctor can test mercury concentrations in your hair and
blood to determine how much mercury is in your body.
High mercury levels in the brain can cause brain cell death and
impair fine motor skills, memory, and focus.
In one research of 129 individuals, those with the highest mercury
levels did significantly worse on fine motor, logic, and memory tests than
those with lower mercury levels.
Mercury is toxic and causes anxiety and depression.
Adults exposed to mercury at work exhibited much greater
depression and anxiety symptoms, as well as being slower at processing information,
according to a study.
Finally, mercury buildup has been linked to an increased risk of
heart disease. This could be due to mercury's role in fat oxidation, resulting
in this illness.
A study of over 1,800 men found that those who ate the most fish
and had the highest mercury levels were two times more likely to die of heart
attacks and heart disease.
On the other hand, other research suggests that excessive mercury
exposure is not linked to an increased risk of heart disease and that the
heart-health benefits of eating fish may outweigh the risks of mercury intake.
How Often Should You Eat Tuna?
Tuna is highly nutritious, including high protein levels, healthy
fats, and vitamins, but it should not be consumed daily.
Adults should eat 3–5 ounces (85–140 grams) of fish 2–3 times a
week, according to the FDA, to get enough omega-3 fatty acids and other
beneficial nutrients.
However, studies show that eating fish with a mercury
concentration of more than 0.3 ppm regularly can raise blood mercury levels and
cause serious health problems. The majority of tuna species exceed this
limitation.
Therefore, most adults should eat tuna in moderation and consider
choosing other fish relatively low in mercury.
When purchasing tuna, choose skipjack or canned light, which have
less mercury than albacore or bigeye tuna.
Skipjack and canned light tuna, and other low-mercury species like
cod, crab, salmon, and scallops can be consumed as part of the recommended 2–3
servings of fish per week.
Try to limit your albacore or yellowfin tuna intake to once a
week. As much as possible, avoid bigeye tuna.
Some Populations Should avoid tuna.
Specific populations are especially vulnerable to mercury and
should minimize or avoid tuna entirely.
Infants, young children, pregnant women, breastfeeding, or
planning to become pregnant are among them.
Mercury poisoning can harm an embryo's development and cause brain
and developmental problems.
Each additional ppm of mercury taken by pregnant women was linked
to a drop of nearly seven points on their infants' brain function test scores
in a study of 135 women and their newborn babies.
On the other hand, low-mercury fish was linked to higher brain
scores in the study.
Children, pregnant women, and breastfeeding mothers are currently
advised to limit their tuna intake and other high-mercury fish, opting instead
for 2–3 servings of low-mercury fish per week.
Final Thoughts
Mercury exposure has been related to various health problems,
including reduced brain function, anxiety, depression, heart disease, and
infant development.
While tuna is high in nutrients, it is also high in mercury
compared to other fish.
As a result, it should be consumed in moderation rather than
daily.
You can eat skipjack and light canned tuna with other low-mercury fish a few times a week, but albacore, yellowfin, and bigeye tuna should be limited or avoided.