(NOTE: nothing in this article should be construed as health advice. Ask your physician if you have questions.)
Tuna is delicious and nutritious, but it is important to keep your tuna consumption within healthy levels. Mercury exposure is an important consideration when adding tuna to your diet.
Tuna packs in tons of protein with less fat than other meats. This makes tuna a great option for anyone looking to add protein to their diet. However, tuna can also have high levels of the toxic heavy metal mercury. Limiting mercury consumption is important to health, particularly for children and pregnant women.
Recommendations for healthy tuna consumption can vary greatly. Some sources say eating more than a serving of tuna each week may put you at risk. However, other sources say that you would need to eat at least three cans of tuna a day for 6 months to risk mercury toxicity.
The United States Food and Drug Administration recommends keeping the consumption of albacore (white) tuna to under 4 ounces per week and skipjack (light) tuna to under 12 ounces per week. These amounts should be lower for children and women who are or may become pregnant.
Mercury and the Food Chain
Mercury is a toxic heavy metal that exists at a low concentration in the ocean. This mercury comes from a number of sources. Though some mercury enters the ocean naturally from sources like volcanoes, the majority comes from human activity. The burning of fossil fuels is the largest contributor. Industrial pollution from waste directly dumped into waterways is another large contributor.
Even with human pollution, ocean water does not contain toxic levels of mercury. Only predators high on the food chain contain dangerous levels of mercury. This is because mercury undergoes a process called biomagnification.
Living things cannot process and remove mercury quickly. When fish eat plankton, the mercury they contain gets concentrated. This happens at each level of the food chain. As a result, large predatory fish like tuna can contain as much as 10 million times more mercury than the water they live in.
Larger fish that are higher on the food chain contain the most mercury. This means larger tuna, like albacore, contain more mercury than smaller tuna like skipjack.
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The Dangers of Mercury Exposure
Mercury is a toxic metal that can have a range of neurological and developmental effects. Though mercury occurs naturally in the environment, fish can contain far higher levels of mercury than their surroundings.
Methylmercury is the form of mercury that exists in fish. Exposure to methylmercury can cause poisoning with a number of neurological and physical symptoms.
According to the United States Environmental Protection Agency, symptoms of methylmercury poisoning include the following:
- Loss of peripheral vision
- Feeling “pins and needles” in the extremities and around the mouth
- Lack of coordination
- Impaired speech, hearing, and walking
- Muscle weakness
Methylmercury has more pronounced effects on children, infants, and developing fetuses. Mercury can cause developmental disabilities in the growing and developing brain. This can cause harm in cognitive function, memory and attention, and fine motor skills.
If you are concerned about mercury poisoning contact your local poison control center or talk to your physician.
So How Much Tuna Should You Eat?
The amount of tuna that is healthy to eat varies with many factors including your age, weight, and type of tuna you are eating.
Due to bioaccumulation, larger tuna contain higher concentrations of mercury. Bluefin, yellowfin, and bigeye tuna are all large, long-lived fish. This means they contain higher levels of mercury.
Large bigeye tuna contain up to 60 micrograms of mercury per 3-ounce serving. This exceeds the EPA's recommended weekly exposure to mercury for a typical adult.
Alternatively, smaller skipjack tuna generally contain closer to 12 micrograms of mercury in the same 3-ounce serving.
Yellowfin and albacore tuna land somewhere in between, containing around 30 micrograms of mercury per 3 ounces.
Given these mercury concentrations, people may safely consume three to four servings of low-mercury tuna per week. Higher mercury tuna should be restricted to one serving per week.
Children Are More Sensitive
Infants, children, and fetuses are far more sensitive to the effects of mercury. As a result, pregnant women and children should further limit their exposure. Mercury can cause developmental problems in children and developing fetuses.
These groups can likely eat up to 4 ounces of albacore tuna a week. However, these sensitive groups should avoid tuna and other large fish altogether to be safe.
Tuna is a great source of protein and other essential nutrients. It can offer the same amount of protein as a serving of chicken or pork with as little as a tenth of the fat! It also provides healthy fats, trace minerals, and vitamin D!
While all the benefits of tuna may make you want to eat tuna for every meal, it is important to make sure you are keeping your tuna consumption to a safe level. If you are concerned about your exposure to mercury, talk to your doctor or another healthcare professional.
Written by Casey Hofford on January 30, 2020.
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