Most fish stories wriggle away from the facts. This one is about hooking the truth.
While many health organizations recommend that Americans eat more fish in their diets, others are warning that the mercury content in certain fish, especially tuna, could compromise health. The Food and Drug Administration, the National Academy of Sciences and the Environmental Protection Agency have all issued warnings about limiting fish meals in “sensitive” groups.
Most vulnerable are pregnant and nursing mothers and young children, but one recent study published in the New England Journal of Medicine indicated that higher-than-normal mercury levels could be linked to increased risk of heart attacks in the general population.
Yet other new research published in the last few weeks has positively associated fish consumption with decreased incidence of stroke and asthma. Plus, one study also published in the New England Journal of Medicine refutes the heart-disease link to mercury.
It’s a bouillabaisse of confusion. Food scientists are worried that too many of us will skip the fish and seafood courses altogether.
“We have developed our new advisory for sensitive populations because people need to be making informed decisions about their fish meals,” said Charles Santerre, associate professor and food toxicologist at Purdue University and spokesman for the Chicago-based Institute of Food Technologists. “But our first point is keep eating fish because it is such an excellent source of long-chain omega-3 fats.”
These omega-3 fats, known by the acronyms EPA and DHA, are most abundant in cold-water fatty fish. Trouble is, some of those fish tend to test highest for mercury levels.
Salmon salvation
Salmon lovers, on the other hand, will be happy to know their favorite fish has nearly undetectable mercury levels. Rainbow trout and sardines, other potent sources of omega-3 fats, are equally effective for getting “good” fats without the downside of mercury.
“There are tremendous health benefits to getting enough omega-3 fats,” said Susan Kleiner, a Seattle-based nutritionist and author of “Power Eating” (Human Kinetics, $17.95). “But we need to get more details about the sources of our fish rather than feel paralyzed to make a decision. . . . “
A 2000 National Academy of Sciences report estimated that 60,000 American women are putting their fetuses “at risk” of brain damage because of the mercury they eat. Symptoms of mercury poisoning (detected in hair and blood samples) center on the nervous system.
Numbness and tingling around the lips, fingers and toes usually are the first symptom. Other symptoms include muscle weakness, fatigue, headache, irritability and inability to concentrate.
Experts have debated what is an unhealthy mercury level in the body, though no one argues that it is most critical in fetuses and children. The controversy translates to identifying the proper threshold for how much is too much in a given fish or seafood creature.
The watchdogs
The FDA considers 1 part per million to be acceptable, while the EPA and NAS are about three to five times more limiting in recommendations. The Environmental Working Group, a consumer organization based in Washington, D.C., and best known for publishing studies about which fruits and vegetables are highest in pesticide residues, is even more adamant about restricting potential mercury ingestion.
“Each person’s choice comes down to two factors: your level of concern about mercury and your current eating habits,” said Gail Frank, a nutritionist and researcher at University of California at Irvine and a spokeswoman for the American Dietetic Association. “If you have a high concern about mercury, irrespective of age or whether you are a pregnant woman or nursing mother, then you should follow the Environmental Working Group recommendations and keep it to about one fish meal per month.”
If you are moderately concerned, Kleiner said, then the EPA and NAS guidelines are more appropriate. Purdue’s “Choosing Fish Wisely” program (on this page) provides a list of fish to eat both regularly and infrequently.
“If you are not as concerned, maybe in a population group without conclusive evidence about mercury,” Kleiner said, “then you would be more inclined to follow the FDA’s recommendations.”
While the FDA holds to its current guidelines, toxicologist Mike Bolger wrote recently in the New England Journal of Medicine that the agency has sought input from its Food Advisory Committee. Among the suggestions are conducting “a detailed assessment of the level of canned-tuna consumption and the associated level of methyl mercury exposure.”
In any case, Kleiner said, it is difficult to require fishermen or manufacturers to provide the exact location of their catch or know the mercury content of the waters. But she said that “size of the fish is a good place to begin” for getting a better handle on the fish supply.
“There is evidence that smaller tuna, for instance, will contain less mercury simply because they are younger fish,” Kleiner explained. “They don’t build up mercury anywhere near the levels of bigger, older fish.”
An added factor is the “forage base” of fish, said Dr. Henry Anderson, chief medical officer at the Wisconsin division of public health. “Tuna live on fish,” Anderson said. “Salmon eat squid and crustaceans,” animals that consume foods with less mercury.
State officials such as Anderson are accustomed to releasing regular reports on freshwater fish levels of mercury and PCBs. These days, an increasing number of state health departments are expanding their purview.
“We have to a take a closer look at items like canned tuna,” Anderson said. “Otherwise, we might be sending people away from one fish to another choice that is problematic.”
Getting on board for a healthier catch
At a neighborhood farmers market in Seattle, fisherman Joe Malley observes the same pattern at his booth week after week from April to mid-October.
“People buy three cans of our tuna,” said Malley, owner of St. Jude Fishing Vessel (visit www.tunatuna.com or call 425-378-0680; it’s not in Chicago area stores). “They eat one can that week and put two away for the winter.”
The reason is because Malley’s St. Jude tuna tastes delicious. Susan Kleiner, a Seattle-based nutritionist, said that it is “unlike anything you have tasted from the supermarket” and “worth the extra dollar or two per can.” St. Jude has several varieties of canned tuna, including olive oil, dill and jalapeno.
As it turns out, Malley and other independent operators may benefit from the growing desire for fish high in healthful omega-3 fats and low in potential mercury content. Malley has conducted several spot mercury tests, and levels have been mostly undetectable.
“Our average fish, which we surface-catch, is about 4 to 5 years old and 15 pounds,” Malley said. “The larger commercial boats are catching 9- to 10-year-olds that are 50 to 80 pounds.”
Scientists have theorized bigger fish have higher mercury residues, especially if, like tuna, they typically feed on other fish.
–B.C.
How mercury ends up in fish
Some basics about mercury can help us make healthier decisions about eating the right amounts and types of fish:
Mercury is part of the Earth’s natural geology. About 2,700 to 6,000 tons of mercury gas are released annually by processes in the Earth’s crust and oceans.
But 2,000 to 3,000 more tons are emitted into the atmosphere each year by human activities, such as burning household and industrial wastes, especially from coal. This extra gas goes right into our land and water. Fish absorb and retain methyl mercury from water as it passes over their gills and as they feed on aquatic organisms such as plankton. Methyl mercury is a neurotoxin that results from chemical transformation of mercury by bacteria. Typically, the bigger the fish, the more mercury it contains.
Mercury readily binds to fish tissues, especially muscle (and typically not fat cells, so mercury content in fish-oil supplements tends to be a non-issue, said Purdue food scientist Charles Santerre).
Nearly all fish have trace amounts of mercury in their systems. Fish in bodies of water near industrial regions are especially prone to increased mercury levels, which is why 40 states now issue regular advisories on mercury content in their freshwater fish.
Most fish range somewhere between 1/100th part per million to half a part per million, comfortably less than the 1 part per million deemed hazardous by the Food and Drug Administration. Nonetheless, the Environmental Protection Agency and the National Academy of Sciences consider more than about a quarter to a third part per million to be unhealthful for mercury-sensitive populations such as pregnant women, nursing mothers and children as old as 15.
–B.C.
Purdue University’s foods and nutrition department has developed a “Choose Fish Wisely” program to guide more sensitive populations about the potential overconsumption of mercury. Here’s what food toxicologist Charles Santerre and colleagues recommend for pregnant women, nursing mothers and children under 15:
1. Keep eating fish. It is optimally healthy to consume at least 8 ounces a week (precooked weight).
2. Before eating sport fish or serving it to your family, consider your state’s advisories on mercury and PCB levels in caught fish. It takes six years to rid the body of PCBs and one year to eliminate mercury. A woman in her childbearing years should choose her fish prudently for the health of future children.
3. To reduce mercury intake from commercial fish, follow the guidelines in this table (remember, the information is directed at sensitive populations; make your own choices accordingly):
High mercury level/Never eat: Tilefish (known as golden snapper or golden bass), swordfish, shark and king mackerel.
Moderate mercury level/One meal per month or less: Tuna steaks, red snapper, orange roughy, pollock, halibut, American lobster, marlin, moon fish, saltwater bass, wild trout, bluefish and grouper.
Low mercury level/One meal per week: Canned tuna, crab, cod, mahi mahi, haddock, whitefish, herring, spiny lobster.
Lowest mercury level/More than one meal per week:
Salmon, oysters, shrimp, farm-raised catfish, farm-raised rainbow trout, flounder/sole, perch, tilapia, clams, scallops and crayfish.
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Visit http://fn.cfs.purdue.edu/anglingindiana/ for more information.
