Mercury in tuna: canned light, albacore, ahi and how much to eat

Mercury from nature and from pollution settles into water, where microorganisms turn it into methylmercury. It builds up in fish and shellfish, and the highest levels are generally in large fish that eat other fish.^[16]

Tuna are fast, big fish near the top of the ocean food chain. But tuna species differ a lot in size and lifespan, and so does their mercury. Canned light tuna is usually a mix of smaller tuna species, most often skipjack. Albacore, sold as canned “white” tuna, is larger and has about three times as much.^[3]

Methylmercury can harm the developing brain and nervous system, which is why the advice is strictest during pregnancy and for young children.^[6]

Fresh or frozen skipjack, the main tuna in canned light, averaged 0.144 ppm in the FDA’s table, though from only 3 samples.^[2]

Bluefin isn’t in the FDA’s table. In a 2010 study of 100 pieces of tuna sushi bought in New York, New Jersey and Colorado, lean bluefin averaged 1.043 ppm, higher than any other kind tested.^[12]

A 5-ounce can holds about 107 grams of tuna once it’s drained, by the USDA’s measure; check your can’s label, since sizes vary.^[8] One ppm means one microgram (µg) of mercury in every gram, so at the FDA’s averages:^[2]

Those are averages. Single cans vary: some canned light samples in the FDA’s testing had none it could detect, and the highest had 0.889 ppm.^[2]

In 2023, Consumer Reports (CR) tested light and albacore tuna from five major brands. Albacore had about three times the mercury of the light tuna, on average, and one light skipjack product tested high enough that CR suggested just one serving a week.^[7] CR’s article has the results by brand.

The FDA and EPA write their fish advice for people who are or might become pregnant, people who are breastfeeding, and children ages 1 to 11. Everyone else can follow it too.^[3]

• Pregnant or breastfeeding: 2 to 3 servings a week from the best choices, which include canned light tuna, or 1 serving a week from the good choices, which include albacore and yellowfin. Skip bigeye.^[1]
• Children 1 to 11: 2 servings a week from the best choices, sized for their age: about 1 ounce at ages 1 to 3, up to 4 ounces at age 11.^[1]

If you weigh less than 165 pounds, the FDA suggests smaller portions, or just 2 servings a week from the best choices.^[3]

Consumer Reports is stricter. It advises avoiding canned tuna altogether during pregnancy. For other adults who eat no other fish, its results supported up to three 4-ounce servings a week of most light tunas it tested, or one of albacore, and no albacore for children.^[7]

Working it out by body weight

The EPA’s reference dose for methylmercury is 0.1 µg per kilogram of body weight a day. That’s an amount likely to be safe every day for a lifetime, set to protect a baby’s developing brain.^[5] Here’s how many cans a week reach it at the FDA’s average levels. These are illustrations, not personal safe limits: real cans vary, other fish count too, and going over the reference dose doesn’t by itself mean mercury poisoning.

If you’re pregnant, might become pregnant or are breastfeeding, and for children, follow the FDA and EPA advice above rather than this table. Their groups were set cautiously, using a 165-pound body weight and 4-ounce servings.^[4]

Tuna is still good food. Four ounces of canned light tuna has about 21 grams of protein and 250 mg of the omega-3 fats EPA and DHA.^[8] Albacore has more omega-3s, about 970 mg per 4 ounces, along with more mercury.^[9]

Methylmercury poisoning can cause “pins and needles” in the hands, feet and around the mouth, loss of side vision, poor coordination, muscle weakness, and trouble with speech, hearing or walking.^[6]

Published case reports describe poisoning after eating a lot of tuna. A fisherman in one ate albacore or yellowfin twice a day, more than 500 grams a day.^[13] In another, a bodybuilder developed problems with balance and nerves after eating large amounts of tuna.^[14] Cases like these don’t show how little is too much, though.

Symptoms aren’t a reliable warning during pregnancy. In past poisoning outbreaks, mothers with no symptoms gave birth to babies with severe disabilities.^[16]

For mercury from fish, a blood test, and sometimes a hair test, can show your exposure.^[15] If you’re worried about how much tuna you eat, or notice symptoms like these, talk to your doctor.

“Ahi” is a name used for both yellowfin and bigeye tuna.^[10][11] Yellowfin is a good choice in the FDA and EPA advice, and bigeye is a choice to avoid, so it helps to ask which one you’re getting.^[1]

Sushi tuna can run higher than the FDA averages. In the 2010 sushi study, lean bigeye averaged 0.871 ppm and lean yellowfin 0.474 ppm.^[12]

• Pick canned light tuna, including canned skipjack, over albacore for everyday tuna salads and sandwiches.^[1]
• Ask which tuna “ahi” is. Bigeye is on the FDA and EPA avoid list, and bluefin had the highest levels in the sushi study.^[1][12]
• Count all your fish. The weekly amounts cover tuna, salmon and everything else together.^[1]
• Mix in the lowest-mercury seafood, like salmon, sardines, shrimp and pollock. See our guide to mercury in fish for the full list.