Holy mackerel! Fish is good for you
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Health-conscious consumers have long been vexed by whether the health benefits of seafood outweigh the risks from toxic substances, such as mercury. Now, two large federally-funded studies have weighed the evidence and reached a definitive conclusion: Eat fish.
The reports -- one from the Institute of Medicine (IOM) and the other from Harvard Medical School, Harvard School of Public Health and Brigham and Women's Hospital in Boston -- analyzed hundreds of research studies and determined that eating seafood may help reduce the risk of heart disease in the general population. In particular, researchers at Harvard found that people who eat one to two servings of fish per week -- especially varieties higher in fatty oils, such as wild salmon -- may reduce their risk of death from heart attacks by 36 percent and the rate of death in general by 17 percent. In addition, the reports found fish consumption by pregnant or nursing women (a population that has recently been skittish about consuming fish) may have a beneficial effect on their infants, including improved visual acuity and cognitive development.
Both reports also assessed the risks of eating seafood -- including exposure to toxic chemicals such as methylmercury, polychlorinated biphenyls (PCBs) and dioxins -- and decided that the evidence of adverse side effects for the general public is inconclusive. The studies do uphold existing recommendations that women who are pregnant or nursing or who may become pregnant should avoid certain types of fish (including shark, swordfish, tilefish and king mackerel) and should limit their intake of albacore, or white, tuna in order to minimize their exposure to the toxic substances. The studies also assert that children under 12 should steer clear of those fish too, and limit their consumption of albacore.
These reports come at a time when sitting down to a meal of fish is fraught with questions. Doctors and medical associations tout fish as a strong source of lean protein and fatty fish, such as salmon or albacore tuna, as important sources of two kinds of omega-3 fatty acids -- eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), "good" fats that help prevent higher blood pressure and irregular heartbeats, both of which can lead to heart attacks. The American Heart Association recommends that people eat fish -- particularly the fatty type -- at least twice a week.
At the same time, federal agencies have issued advisories warning women of reproductive age to restrict their fish intake to limit the amount of toxic substances to which they are exposed, especially methylmercury, which can cause permanent neurological damage in infants and fetuses. And most states have issued advisories warning of the toxic substances found in fish caught locally -- including mercury and PCBs, industrial chemicals banned since the 1970s that persist in the environment and have long been suspected of causing cancer and reproductive problems.
In March, 2004, the U.S. Food and Drug Administration and the U.S. Environmental Protection Agency issued a joint advisory on methylmercury in fish. While it stated that fish and shellfish are an important component of a healthy diet, it warned women who are pregnant, nursing or planning to become pregnant to avoid those four types of fish that contain high levels of mercury -- shark, swordfish, king mackerel and tilefish -- and to limit their intake of albacore tuna, which has more mercury than "light" tuna.
The conflicting messages are causing confusion among consumers. "It can be frustrating," says Robert Kressly, 36 years old, who tries to eat fish three times a week to help lower his cholesterol and takes fish-oil supplements that, he says, relieve symptoms of his bipolar disorder.
But to keep straight which fish are healthy and which have too much mercury or other contaminants (plus which are environmentally sound to eat), Mr. Kressly carries a small booklet in his wallet, published by an aquarium, that lists its guidelines of the best and worst seafood choices. Now, when a waiter tells him the daily specials, he pulls out the guide. "People think I'm hoity-toity, but I'm just trying to avoid the risks," says Mr. Kressly, an operations manager for a national chain of self-storage facilities who lives in Pennsauken, N.J.
For the Harvard report -- "Fish Intake, Contaminants, and Human Health," supported by the National Institutes of Health and published in JAMA, the Journal of the American Medical Association -- the researchers performed a meta-analysis, pooling the data of more than 200 existing studies on the benefits of fish and fish-oil consumption on cardiovascular health in adults and on the neurological brain development of babies, as well as the health risks of methylmercury, PCBs and dioxin found in fish.
The authors of the Harvard report are explicit in their conclusion: The benefits of modest seafood consumption far outweigh the potential risks. In their analysis, the researchers looked at wide variety of commonly consumed fish. They determined that the cardiovascular health benefits of wild-salmon consumption, for example, outweigh the cancer risks by 900 to one, while the benefits of farm-raised salmon outweigh the risks by 300 to one.
"The number one cause of death in the U.S. is coronary heart disease," says Dariush Mozaffarian, a cardiologist at Harvard Medical School and Harvard School of Public Health who co-authored the study. "If fish intake reduces that by approximately one-third, there's potential to save thousands of people from coronary heart-disease deaths per year."
By contrast, the IOM report -- "Seafood Choices: Balancing Benefits and Risks," sponsored by the National Oceanic Atmospheric Administration with support from the FDA -- is more measured in its findings, which weren't based on pooled data but on the qualitative examination of hundreds of studies. The report determined that people may be able to reduce the risk of heart disease by eating seafood, although it isn't clear if this is because of the protective effects of omega-3 fatty acids or because substituting the lean protein of fish for a fatty cut of meat reduces one's intake of saturated fat.
At the same time, the report concluded that much of the scientific evidence for both the benefits and the risks of seafood is preliminary or insufficient. It says there aren't enough reliable data about contaminants and little evidence of how the beneficial effects of seafood may counteract some of the risks. It determined that people who have already had heart attacks may not necessarily reduce their risk of future attacks by eating fish, as previously thought. It also decided that it is unclear whether seafood can reduce a person's risk for other diseases, such as diabetes, cancer or Alzheimer's.
Ultimately, both reports reiterate the existing recommendations for seafood consumption. Consistent with the FDA-EPA joint advisory on methlymercury in fish, they suggest that women who are or may become pregnant or who are breastfeeding may benefit from eating seafood, especially fatty varieties that are relatively higher in concentrations of omega-3 fatty acids. The Harvard study says that women in this category should aim for up to 12 ounces of fish per week, while the IOM report says that two servings of three ounces each would be sufficient, although up to 12 ounces is safe.
The IOM report also said children up to 12 years of age may benefit from consuming seafood, especially those types that are relatively higher in concentrations of EPA and DHA, such as salmon. This age group could reasonably eat two three-ounce servings per week (or an age-appropriate size), and they can safely consume up to 12 ounces per week.
Healthy adolescent males, adult males and females who won't become pregnant may reduce their risk for future cardiovascular disease by consuming seafood regularly, for example two three-ounce servings of seafood per week. And adults who are at risk of cardiovascular disease may reduce that risk by consuming seafood regularly (again, two three-ounce servings per week). People who consume more than two servings per week should make sure they are eating a variety of different types of seafood, to diminish their risk of exposure to contaminants from a single source.
First Published October 18, 2006 12:00 am