The belief that the omega 3 fats found in oily fish can help prevent heart disease is far from proven, a new British study contends.
U.S. experts agreed with that statement, but also stressed that people without heart disease will suffer no harm from consuming fish, and quite possibly could do themselves some good. And there's clear proof that omega 3 consumption helps people who already have had heart attacks or other cardiac problems, they added.
The report, published in the March 25
British Medical Journal, summarized findings from 89 studies aimed at assessing the effects of omega 3 consumption from fish or supplements on total mortality, heart problems, strokes and cancer.
The picture is "mixed," concluded Lee Hooper, a lecturer in research synthesis and nutrition at the University of East Anglia in Norwich, England, and lead author of the report. Two major studies did show a benefit, but the most recent large study did not, she said.
One problem in interpreting the findings is that most of the trials included people who already had cardiac problems such as heart attacks or angina. Putting all the studies together produced conclusions that could be described as equivocal, Hooper said.
"If you put the results all together, for every 100 deaths in the control group (those who didn't get omega 3), you see 87 deaths in those who took supplements," she said. "But that could be as low as 74 and as high as 102; our best guess is 87."
What's needed to determine the true preventive benefits of omega 3 consumption are more and larger trials, Hooper said. "At the moment we just aren't sure, so we should be cautious," she said.
That is pretty much the conclusion reached by an expert panel assembled in June 2004 by the U.S. National Heart, Lung, and Blood Institute.
"In terms of primary prevention, we still don't have the answer, and the conclusion of the panel was that additional studies were needed before making recommendations to the general public," said Dr. Eliseo Guallar, associate professor of epidemiology and medicine at the Johns Hopkins Bloomberg School of Public Health, and a member of the panel.
Those studies, which would be expensive, haven't been started yet, Guallar said. "And even if they were done, we wouldn't know the results for five, six, seven years from today," he said.
There's no question about the value of the omega 3 in fish oil for people with existing heart problems, Guallar said. One study of people who suffered heart attacks showed that taking 850 milligrams of fish oil a day substantially reduced their risk of sudden death, he said.
But while fish oils are "most promising for primary prevention" in people without heart disease, "we still don't know for sure," he said. Still, he endorses the American Heart Association's recommendation of eating at least two fish meals a week.
The heart association also recommends consumption of plants such as soybeans, canola and flaxseed, which contain a different version of omega 3 oils.
Alice R. Lichtenstein, professor of public health and family medicine at Tufts University School of Medicine and vice chair of the heart association's nutrition committee, isn't so sure about the plant part of the recommendation. It's not certain that the omega 3 in plants has the same benefits as the fishy kind, she said.
And even when it comes to fish consumption, "the jury is still out," Lichtenstein said. Nevertheless, eating fish is a good idea, in part because it keeps that much fatty meat out of the diet, she said, adding, that "the secondary benefit of what you don't eat supports moderate fish consumption."
But be careful about what kind of fish you eat, Lichtenstein added. Not all fish are rich in omega 3, and some commercial fish products are fried, which takes away a lot of the benefit, she said.
Mackerel, lake trout, herring, sardines, albacore tuna and salmon are good sources of omega 3, according to the heart association.
Source:
Oily fish and omega 3 fat supplements, BMJ
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