Is seafood a heart saver?
That's how most scientists currently see the evidence that fish can reduce the risk of heart disease. Their hopes are not nearly as high as they were in the early 1980s, when researchers discovered that Eskimos in Greeniand rarely suffered heart attacks.(2)
"In studies of Eskimos - who, incidentally, ate seal and whale rather than fish - low rates of coronary disease were found," explained Katan. "But their diet and lifestyle were quite special and most of them died before reaching middle age."
Since then, several studies in the Netherlands and the U.S. have reported a lower risk of heart disease among fish-eaters than among people who eat no fish. But a few other studies have seen no link. And in 1995, two key seemingly contradictory studies complicated the debate:
* The Harvard School of Public Health Study. In 1986, Alberto Ascherio and colleagues sent diet questionnaires to nearly 45,000 male dentists and other health professionals aged 40 to 75.(3) After six years of follow-up, Ascherio found that the men who ate six or more servings of fish a week had no lower risk of heart disease than the men who ate only about one serving a month.
The headlines were discouraging. "Study Finds Fish-Heavy Diet Offers No Heart Protection," reported the New York Times. * The University of Washington Study. David Siscovick and co-workers interviewed 334 patients - or spouses of patients - who suffered cardiac arrest in the Seattle area.,l They then compared the victims, diets - and in some cases, their blood samples - to those of 493 similar people.
The results: Compared to people who ate no fish, those who reported eating one serving of fatty fish (like salmon) a week had half the risk of a cardiac arrest.
The headlines were jubilant. "Even a Little `Fatty' Fish Cuts Heart Risk," declared USA Today.
A contradiction? Not necessarily.
SOME BEATS NONE
"There's no real conflict between these two studies," says Ascherio. In Seattle, the hearts of people who consumed little or no seafood were in greatest danger. And it looked as though the Harvard study would have yielded the same results if more of the health professionals had eaten little or no seafood.
"We found the highest mortality in the group math the lowest fish consumption - those who ate fish less than once a month," says Ascherio. "But the results were not statistically significant," he adds, because so few health professionals were infrequent fish-eaters.
"We would interpret both studies to mean that a small amount of fish is advisable but there's no clear advantage above the once-a-week range," says Ascherio.
Another key difference separates the two studies. "Harvard focused on all kinds of heart disease," says Siscovick. "Our study focused only on cardiac arrest."
Most heart attacks are myocardial infarctions - that is, some of the heart muscle (myocardium) dies because the coronary arteries that nourish it get blocked. The usual culprit: a blood clot that gets stuck in a partially clogged artery.
In cardiac arrest (sudden death), on the other hand, the heart stops beating because the electrical impulses that control its rhythm go awry (arrhythmia).
"People collapse and die unexpectedly if they're not resuscitated," says Siscovick. "Even in Seattle, where the paramedics are some of the best in the world, eight out of ten people who go into cardiac arrest die. It's a highly lethal condition."
The Harvard study couldn't draw any conclusions about sudden death. "We didn't have enough in our study to get any stable estimates of risk," explains Ascherio.
Siscovick got interested in cardiac arrest because there is evidence that the fats in seafood can protect the heart,s rhythm.
"In animal studies, the vulnerability to arrhythmia is markedly reduced by diets enriched with the fatty acids in fish," he explains.
For example, it's tougher to induce arrhythmia in monkeys fed fish oil than in monkeys fed either saturated fats or polyunsaturated vegetable fats like sunflower oil.(5) "Fish oils may influence risk through a direct effect on the membrane of the heart muscle cells," says Siscovick.
What about in humans? In a study in Wales, people who already had heart attacks were told to eat more seafood.r, "The overall incidence of heart attacks was not affected,,, says Ascherio. "But mortality was lowered. That's what you'd expect if seafood alters an electrical mechanism to reduce the severity of a heart attack."
Nevertheless, he says, "we can't draw firm conclusions that fish has an effect on sudden death." Others agree. We need more randomized clinical trials," says Siscovick.
If later studies contradict the Seattle findings, it wouldn,t be the first time that fish@r, more precisely, fish oil - flopped. For example:
* Early studies suggested that fish oil capsules could prevent arteries from re-clogging after they were unclogged by angioplasty. Later, a large, well-designed clinical trial found no benefit.(7)
* Clinical studies initially suggested that fish oil capsules always lower LDL ("bad") cholesterol. But later studies disagreed.(8)
* Contrary to earlier reports, fish oil capsules did not prevent high blood pressure in people at risk for hypertension.(9)
Fish oil isn't a total flop. It does lower high blood triglyceride levels, but only when used in high doses.(10) "You have to take eight to twelve capsules a day, and you should do it under a doctor's supervision, because fish oil can raise LDL," says William Connor of the Oregon Health Sciences Center in Portland.
And while it's possible that fish oil capsules may reduce the risk of blood clots by making blood less "sticky," aspirin is far more effective.'
Despite the uncertainty, it's reasonable to eat seafood once a week or so. If the Seattle study turns out to be right, you should make that a fatty fish like salmon or sardines. If nothing else, eating seafood instead of red meat cuts artery-clogging saturated fat.
Says Connor: "l recommend that everyone eat two to three servings of fish a week to prevent heart disease."
Yes, seafood is healthy ... when it,s first caught, and Cmaybej if you cook it at home. But seafood,s fat and sodium numbers can climb sky@high when you,re dining out. Fried seafood is even high in artery@clogging fat.
[Tabular Data Omitted]
(1) Numbers from McDonald's. (*) = does not include trans fat. Foods are ranked from least to most total fat. All numbers have been rounded.
Source: Company information and Nutrition Action Healthletter restaurant studies.
(1) New Eng. J Medicinem 332: 1024, 1995. (2) Amer. J Clinical Nuirition 33:2657, 1980. (3) New Eng. J Medicine 332:977, 1995. (4) J Amer. Med. Assoc. 274: 1363, 1995. (5) Amer. J Clinical Nutrition 58: 666, 1993. (6) Lancet 2: 757, 1989. (7) Circulation 90: 2248, 1994. (8) Annals of Internal Medicine 109: 465, 1988. (9) J Amer. Med. Assoc. 267: 1213, 1992. (10)New Eng. J. Medicine 312: 1210, 1985.
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|Publication:||Nutrition Action Healthletter|
|Article Type:||Cover Story|
|Date:||Nov 1, 1996|
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