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Mercury in Seafood


For years, the media has underlined the valuable dietary contributions of fish, and the positive press is well deserved. "Brain food" and "heart-healthy," fish is high in protein and low in saturated fat. It contains omega-3 fatty acids as well as nutrients like DHA, EPA and selenium. Recent studies by doctors at Harvard Medical School and Brigham and Women's Hospital conclude that just one or two servings of fish per week (especially those high in fatty acids, like salmon) cuts the risk of death by 17 percent and the risk of coronary death by 36 percent.

All fish-related news hasn't been upbeat, though. Stories about the dangers of mercury in fish and shellfish might have you wondering if fish remains a good food choice after all. There are plenty of variables to consider and debate to be found, but most experts agree that the benefits of eating fish outweigh the possible risks of mercury contamination-as long as you make well-informed decisions about which fish you eat and in what quantities. Learn more about commonly asked questions on this issue below:

How does mercury get in fish?

Mercury is a naturally occurring metal, but it's also released into the environment via industrial pollution. Once rained or melted into the waterways, mercury is converted by bacteria into a more toxic form of the metal, methylmercury. As fish feed in these waters, they absorb the methylmercury. Most fish and shellfish have at least trace levels of it. And some fish-those that eat other fish, are larger, and live longer-have higher levels than others. These include swordfish, king mackerel, shark, some kinds of tuna and tilefish. The Chilean sea bass, which is often sold in restaurants, and big-eye tuna, which is sometimes used to make sushi, also test high in mercury. Fish and shellfish low in mercury include catfish, cod, crab, flounder/sole, grouper, haddock, herring, lobster, mahi-mahi, ocean perch, oysters, rainbow trout and farmed trout, salmon, sardines, scallops, shrimp, tilapia, and pollock. Cooking does not affect the mercury content of fish.

Why is mercury a problem?

Mercury has been linked to cognitive and physical disabilities. The main concern is that mercury can block the development of nerve cells in the brain-which puts developing infants and young children in the high-risk group for mercury consumption. Pregnant and nursing women, as well as women who are thinking of becoming pregnant, are also placed in this high-risk category because the mercury that accumulates in the bloodstream is passed along to a developing fetus and nursing baby. While studies have focused primarily on the dangers of mercury to babies and young children, high levels can also have detrimental neurological and cardiovascular effects on adolescents and adults.

What's being done about mercury in fish?

The Food and Drug Administration (FDA) regulates fish and seafood that's sold in the U.S., and the Environmental Protection Agency (EPA) monitors mercury in the environment and released by industry. In recent years, the FDA and the EPA have stated that while fish still has an important place in a healthful diet, young children, pregnant women, nursing mothers, and women of childbearing age should avoid consuming fish that are high in mercury. The FDA also advises that this high-risk group to limit consumption of other fish to 12 ounces (about two meals) per week; the EPA recommends 8 ounces (one meal) per week, and 3 ounces per week for young children and 8 ounces (one meal) per week for the rest of the high-risk group.

Other organizations are working to help consumers evaluate the role of fish in their diets. In a 2006 report titled "Seafood Choices: Balancing Benefits and Risks," for example, the National Academy of Sciences concluded that fish is high in nutritional quality and excellent for coronary heart health. The group states that children (up to age 12), pregnant women or women who may become pregnant, as well as women who are nursing, will benefit from eating seafood. They suggest that this high-risk group avoid fish that is high in mercury, but otherwise consume about 6 ounces (and up to 12 ounces) of fish per week. For adolescents and adults who are not in the high-risk category, they recommend up to 6 ounces per week (two 3-ounce servings) of fish. For those who eat more than two servings per week, they suggest choosing from a variety of seafoods, to insure that they not consume primarily one type of fish that may be high in mercury. They also recommend increased governmental monitoring of seafood for contamination.

To help at the food counter, consumer groups advocate the labeling of all fish and shellfish products (these standardized labels would identify which choices are higher in mercury) and posting advisories (to alert those at high-risk) at fish counters. Some stores voluntarily post signs, but the government requires no mandatory signage or labeling at this time. It's up to you to ask questions and make your own recommendations-for adequate information for all consumers.

I'm confused about tuna!

Understandably. There are some general guidelines you can follow, though. Because larger tuna are more long-lived, they have higher levels of mercury. So tuna steaks are higher in mercury than smaller tuna that's used for canning. In addition, "chunk light" tuna generally has less mercury than "white" or "albacore" tuna. There are some exceptions, however. In one study, 6 percent of the light-tuna samples contained as much or more mercury than the albacore tuna. This might be because light tuna is made from different varieties. While most is "skipjack," a type of tuna that's low in mercury, some is "yellow fin," which has higher mercury content. Unfortunately, albacore is the only specific type of tuna that's routinely labeled. In addition, imported tuna has tested twice as high in mercury than tuna canned in the U.S. You can ask your grocer about the source of your store's canned tuna.

Where can I learn more?

National Cooperative Grocers Association, www.ncga.coop


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