Canned Tuna May Contain 'Dangerous Spikes' of Mercury, New Report Finds

Photo Illustration by Michela Buttignol for Verywell Health; Getty Images

Canned tuna makes for an easy and cheap meal, but this pantry protein source may contain dangerous levels of mercury, a neurotoxin especially harmful to pregnant people and young children.

Food safety experts at Consumer Reports tested mercury levels across five brands of canned tuna and found that 20% of the samples tested contained "dangerous spikes" of mercury.

Currently, the Food and Drug Administration (FDA) recommends that pregnant people eat eight to 12 ounces of fish a week, but choose options that contain lower mercury levels. According to the new research, though, unpredictable spikes in some canned tuna may exceed the recommended limit for pregnant people, putting the health of a fetus at risk.

James E. Rogers, PhD, director of food safety research and testing at Consumer Reports, told Verywell in an email that it's best for sensitive populations such as pregnant people to avoid eating tuna.

Mercury is a natural element that can be released via volcanos or human activities like mining. Once mercury gets into the water, it's converted into toxic methylmercury and consumed by fish. As fish eat other fish, more and more methylmercury gets built up in their systems.

Methylmercury exposure is linked to neurodevelopmental delays in infants and fetuses as well as heart disease risks in adults, according to Elsie M. Sunderland, PhD, a professor of earth and planetary sciences at Harvard University.

According to Rogers, tuna is high up in the ocean food chain, and it can absorb any mercury from the fish they eat. While tuna is not the biggest fish in the ocean, it's one of the most popular seafood consumed by people of all ages.

According to the Consumer Reports findings, albacore tuna cans contained on average three times more mercury than light or skipjack tuna cans. Since albacore tuna are larger and tend to live longer, these fish have more opportunities to build up mercury in their systems.

Eating seafood is the main way Americans are exposed to mercury. However, according to a survey that accompanied the Consumer Reports research, about half of the respondents said they didn't know different types of tuna can have varying levels of mercury and 18% of them didn't realize that canned tuna has any mercury.

You shouldn't have to cut out all your seafood consumption because of concerns about mercury exposure. "Rather than avoiding seafood consumption—which is mainly a healthy food—it would be beneficial to support efforts to reduce pollution levels in the environment that will translate into lower fish mercury concentrations," Sunderland said.

She suggested that pregnant people and people who may become pregnant "should continue eating some seafood to obtain essential long-chain omega three fatty acids or take an algal supplement for long-chain omega 3 fatty acids (EPA and DHA)."

Omega-3 fatty acids support healthy brain development and reduce heart disease risk. While tuna is a good source of omega-3s, lower-mercury seafood choices, like salmon and shrimp, also provide this essential nutrient.

Vulnerable groups may want to avoid tuna, but researchers at Consumer Reports said non-pregnant adults can safely consume three cans of light or skipjack tuna each week or up to 4oz of albacore per week.

Generally, experts say that seafood is part of a healthy diet as long as most people stick to low-mercury options. Shrimp, salmon, pollock, and herring all fall into the low mercury category and could be good alternatives to seafood with high mercury levels.

"You cannot cook this heavy metal out of your tuna, so it is best to start with products that contain lower mercury levels," Rogers said.

Since mercury is a neurotoxin found in fish, pregnant people or people who may become pregnant should speak with a trusted healthcare provider about the risks of consuming tuna or other seafood.

Food and Drug Administration. Advice about eating fish.

Environmental Protection Agency. How people are exposed to mercury.

Consumer Reports. How worried should you be about mercury in your tuna?

Environmental Working Group. U.S. fish advice may expose babies to too much mercury.