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Can Too Much Tuna Cause Mercury Poisoning?

November 11, 2023

When you’re in a pinch for a wholesome snack or a quick dinner, tuna offers an easy (and affordable) option.

But if you’re reaching for that can of tuna more than once or twice a week, you could be putting yourself at risk.

Here’s what an expert has to say.

It isn’t a myth – tuna does contain mercury.

Methylmercury, to be exact.

“Methylmercury is typically absorbed by the gastrointestinal tract, and then distributed to different parts of the body, especially the nervous system and brain,” says Michael O’Neill, MD, a Hartford HealthCare Medical Group internal medicine specialist. “If enough mercury is consumed, you’ll start to see signs of chronic mercury poisoning.”

These symptoms can include:

• Memory loss
• Irritability
• Tingling
• Changes to taste, vision, and smell

“There are some medications that can be given to help pull mercury out of the body, but the best treatment is usually just to avoid unnecessary mercury exposure. Unfortunately, it can take weeks or even months for mercury to leave the body,” Dr. O’Neill notes.

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But that doesn’t mean you can’t eat it.

Like most foods, it’s okay to eat tuna in moderation.

“According to the FDA, the average adult can safely eat about six to nine ounces of tuna per week,” says Dr. O’Neill. “That typically works out to one to two cans, depending on the size.”

But there are some exceptions.

“Children and low weigh adults should eat even less. Pregnant or breast-feeding mothers should avoid tuna entirely,” Dr. O’Neill adds.

If you eat tuna all the time, try substituting salmon or cod, which both contain far less mercury.

Some brands – and fish – have more mercury than others.

Here’s the most important takeaway – check the label before you buy a can of tuna. Smaller tuna accumulate less mercury, which makes some brands safer than others.

Made with Skipjack tuna, common brands like Canned Light or Chunk Light only have about 20 micrograms of mercury in a five ounce can. Larger fish like Albacore and Yellowfin have up to 50 micrograms per can, while Atlantic Bluefin, the largest tuna, can have as many as 283 micrograms per five ounces.

If you’re trying to keep your mercury intake low – but not your tuna intake – be sure to choose a can made with a smaller fish.

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When it comes to tuna, buy local.

The size of the fish matters, but it isn’t the only factor.

“There are a few things to consider when you’re buying tuna,” says Dr. O’Neill. “Trustworthy companies will be transparent about where the fish was caught. Try to buy tuna caught from local or U.S. fisheries, as they tend to be in better health.”

If you’re not sure where the tuna was caught, don’t buy it, says Dr. O’Neill. He also warns against buying imported tuna, especially those caught in the Indian Ocean.

And it isn’t just where the tuna was caught, it’s also how.

“Look for labels like line caught, pole caught or FAD (fish aggregating device) free. These are the most sustainable practices, and are safest for other sea life,” he says.