Healthy Eaters Beware: Tuna Carries Hidden Dangers

Medically Reviewed by Jacqueline Brooks, MBBCH, MRCPsych
From the WebMD Archives

March 13, 2001 -- Headlines about mad cow disease and foot-and-mouth disease on top of decades of warnings about red meat have many consumers opting for fish over steak. But new evidence suggests that fish, especially tuna, has health risks, too -- risks that can't be cooked away.

A study in the Journal of the American Medical Association details the growing problem of histamine poisoning caused by tuna. Histamine poisoning causes a rash, diarrhea, cramping, vomiting, a tight feeling in the throat, facial flushing, and headache -- symptoms that are disabling but temporary and usually not fatal.

Histamine poisoning is a difficult public health problem because "you can't cook histamine poisoning out of fish. Once it is there, it stays," says Walter Staruszkiewicz, MA, of the Washington Seafood Laboratory at the FDA. Staruszkiewicz has been tracking histamine in fish for more than 30 years.

So all the advice about careful preparation and thorough cooking are useless in this case, says Karen Becker, DVM, MPH, a CDC expert who is a co-author of the new study.

People who have a case of histamine poisoning usually "just think they have had an allergic reaction to fish," she says.

Moreover, Becker says that more cases of histamine poisoning, also called scombroid poisoning, are being seen because more Americans are eating fish more often. Case in point: Last fall, the winning burger recipe in Sutter Home Wineries' "Build a Better Burger" contest was a tuna burger with "Wowee Maui Salsa."

According to Becker, there were only four cases of histamine poisoning in North Carolina from 1994 to 1997. "In our study, we identified 22 cases from July 1998 to February 1999," she says.

Histamine is the product of the decomposition of a chemical compound found in most fish. The chemical, called histidine, begins to break down and form histamine as the tuna dies. The only way to stop the process -- and prevent histamine from contaminating the fish -- is to freeze the tuna rapidly after it is caught, says Staruszkiewicz.

He says the fish must be frozen within 6 hours or histamine will begin to form. This especially true for two very popular types of tuna -- yellow fin and skip jack -- because they are caught in warmer waters, he says. Albacore, which is generally harvested in colder waters, has a slightly lower risk for histamine poisoning, says Staruszkiewicz. Generally, he says that all salt-water fish pose a histamine risk.

The FDA considers a "safe" level of histamine to be no more than 50 ppm, a designation used to describe "parts per million." In the study by Becker and colleagues, the tuna that caused poisonings had from 213 to 3,245 ppm, she says. "Eighteen people ate tuna burgers served in restaurants in North Carolina, two people ate tuna salad, and two ate tuna filets," she says. Especially disturbing was the finding that "21 cases involved tuna served at a very upscale, fancy restaurant."

Staruszkiewicz, who wasn't involved in the JAMA study, says that it isn't surprising that histamine-contaminated tuna could be served at a four-star restaurant, because identifying contaminated tuna is very difficult.

Unlike other types of contamination, histamine doesn't cause a noxious odor and doesn't really change the appearance of the fish after it has been cleaned. "You have to examine it at the point of butchering, and even then you really have to know what you are looking for," he says. For those who have the chance to examine a "fresh catch," Staruszkiewicz suggests that you "look inside the gills, which should be red, not brown."

Becker advises "poking the fish to see if it bounces back [which is good] or if the indentation remains."

While that may work for "fresh" fish, it doesn't help with canned products, and Staruszkiewicz says there are reports of histamine poisoning associated with canned fish products, although those reports have decreased as the large canning operations have perfected the use of refrigeration and freezing on commercial fishing vessels.

Staruszkiewicz says he first began tracking histamine as the result of a large criminal investigation of StarKist Tuna in the early 1970s. At that time, so little was known about histamine that "the StarKist scientists thought that 200 ppm was a safe level." Work by Staruszkiewicz subsequently established the safe levels used for FDA guidelines.

So how can one pick a "safe" tuna? Staruszkiewicz has this advice: Stick to frozen products, unless you're purchasing a truly local product. He lives in the Maryland suburbs of Washington, D.C., and says, "I only buy catfish fresh because I know it is really fresh."

With the popularity of fish, he tells WebMD that "consumers are willing to pay top dollar for fresh seafood. But how fresh can it be if it was fished down in Chile, shipped to Louisiana, and then trucked to Pittsburgh?"