News Coverage
Too much fish has its risks
Published November 20, 2002
QUESTION: I am concerned over mercury in fish. My understanding is that deep-sea fish are now becoming dangerously high in mercury. Can you comment on this topic? Thanks.
A.S., Hanover, N.H.
ANSWER: Mercury is a naturally occurring element in our environment, so it is impossible to avoid it entirely. The body has an ability to eliminate mercury, albeit slowly. One of the ways the body casts off mercury is to incorporate it into hair, so hair analysis is often used to measure the level of exposure. A contaminant such as mercury enters the food chain when industrial pollution gets into the water and becomes incorporated into basic forms of life, such as algae or plankton.
The "you are what you eat" adage holds true in the ocean as it does on land. The pollutants work their way up the food chain as smaller creatures become the food source for increasingly larger creatures.
The amount of mercury in a given fish depends on how long it has been in polluted waters and how much mercury was in the food it consumed.
Measurements of mercury levels from the 1999 National Health and Nutrition Examination Survey found that approximately 10 percent of the women tested were close enough to the safety limit to make it prudent to encourage reducing exposure to mercury in food.
Pregnant and lactating women, infants and young children are at higher risk because mercury intoxication can cause kidney problems and irreversible neurological damage in a growing body. In fact, the National Academy of Sciences estimates that 60,000 babies are born every year with neurological damage brought about by mercury.
Fish sitting atop the oceanic food chain tend to have the highest levels of contaminants. In the case of mercury, the Food and Drug Administration issued an advisory that women of child-bearing age should not consume shark, swordfish, king mackerel or tilefish.
The risk of mercury in salmon appears to be minimal. In fact, the FDA states that limiting consumption is unnecessary for salmon, canned tuna, shrimp, pollock, cod, catfish, clams, flatfish, crabs and scallops. These fish make up about 80 percent of the seafood we eat.
The FDA notes that these varieties typically contain a low level of mercury and that few people eat more than the suggested weekly limit (2.2 pounds) of fish with this level of mercury contamination.
There is, however, no consensus that this is all that needs to be done. The Environmental Working Group, a not-for-profit environmental research organization, has a more extensive list of fish to avoid. The group recommends that pregnant women, nursing mothers and all women of childbearing age should not eat tuna steaks, sea bass, oysters from the Gulf Coast, marlin, halibut, pike, walleye, white croaker or largemouth bass.
These are in addition to the FDA's recommendation to entirely avoid shark, swordfish, king mackerel and tilefish.
The Environmental Working Group goes on to state that women in this group should eat no more than one meal per month of canned tuna, mahi-mahi, blue mussels, Eastern oysters, cod, pollock, salmon from the Great Lakes, blue crab from the Gulf of Mexico, wild channel catfish or lake whitefish. The "safe" fish for mercury, according to the group's data, include farmed trout or catfish, shrimp, fish sticks, flounder, wild Pacific salmon, croaker, haddock, and blue crab from the mid-Atlantic.
Canned tuna presents an interesting issue. On one side we have the fact that the tuna that goes into cans is usually caught in the open ocean, far from polluted areas. The flip side is that tuna are high up on the food chain, and even if they don't hang around in polluted waters, the fish they dine on may contain dangerous pollutants.
It turns out that the chunk light canned tuna tends to have less mercury than white albacore.
All this tells us that it makes sense to be cautious, but to do so with a reasoned approach.
We can all benefit from the high-quality protein and healthful omega-3 fats found in seafood. There are many choices when it comes to seafood, and it makes sense to exercise your options and not stick with any one variety.
For those who want more information about mercury, check with the National Library of Medicine at: www.nlm.nih.gov/medlineplus/mercury.html
General-interest questions about nutrition can be mailed to: Ed Blonz, Focus on Nutrition, P.O. Box 120191, San Diego, CA 92112-0191, or sent via e-mail to UTFood@blonz.com.
Ed Blonz, Ph.D., a nutritional scientist based in Northern California, is the author of seven books on foods and nutrition.