And, Gibbons added, "there has been no cases of mercury toxicity from normal consumption of commercial seafood in any peer-reviewed study. Nobody has ever gotten sick from the methyl mercury from the normal seafood you find in restaurants and supermarkets."
Furthermore, he said, the FDA guidelines have an uncertainty factor built in that limit mercury exposures to levels 10 times lower than the lowest levels associated with adverse effects.
"Canned tuna is safe," Gibbons said. "Consumers should trust that canned tuna continues to be a safe, healthy source of lean protein and omega-3 fatty acids."
While Gerstenberger concurred that much of the mercury found in the oceans is naturally occurring, human activity -- such as incinerating batteries and industry -- has contributed, he said.
Mercury content in fish is highly dependent on their environment, including where they are caught and the size of the fish. Gerstenberger said he would not reveal the brand names tested in the study because he expected those with the highest mercury levels would flip-flop throughout the year, depending on where their suppliers were fishing.
The health effects of mercury poisoning include central nervous system damage, hearing loss and vision problems. Though there are no specific mercury warnings for anyone outside of the high-risk groups, Gerstenberger recommended other adults also eat tuna in moderation -- although what that amount is may be anyone's guess.
"There are plenty of health benefits that have been documented from eating tuna and other fish," Gerstenberger said. "It's important for consumers to weigh all of that and make a decision."
The researchers called on federal regulators to require canned tuna producers to provide detailed information to consumers about the mercury content and to disclose tuna harvest locations.
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