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Why doesn’t fish oil prevent heart attacks anymore?

Maybe it depends on the drugs you're taking.

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“Fish Oil Claims Not Supported by Research,” read the headline in the New York Times. “Flimsy evidence that fish oil helps the heart,” the Sarasota Herald-Tribune wrote.

Are you taking fish oil pills because you thought this would prevent fatal heart attacks? What gives?

“People who eat a diet that’s high in fish have a lower risk of heart attacks and strokes in many observational studies,” says JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospi­tal in Boston.

But those studies, which observe a lower risk in fish eaters, can’t prove cause and effect. “Fish may replace foods—like red meat—that increase risk,” notes Manson. “Or fish eaters may have other behaviors that lower their risk.”

To prove cause and effect, researchers need a trial that randomly assigns people to take either a placebo or fish oil pills. Pills are used since it’s tough to find a placebo for salmon or tuna, and there’s evidence that it’s the ome­ga-3 fats in fish oil that protect the heart.

These kinds of randomized, controlled trials of fish oil conducted 10 to 15 years ago in Italy and Japan did seem to show that fish oil protects the heart.

It worked here.

For example, an Italian trial called the GISSI Prevention study tested fish oil on roughly 11,000 men and women who had already suffered a heart attack. They were randomly assigned to take the omega-3s EPA and DHA (850 milligrams total) or vitamin E (300 mg) or both every day or no pills at all. (There was no placebo, and the participants knew which pills they were taking, but researchers still consider the results important.)

After 3½ years, the risk of dying of a sudden death heart attack was 45 percent lower in those taking EPA and DHA than in those who took no pills. Vitamin E had no impact on heart attacks.

“But more recent randomized trials are casting doubt on the heart benefits of omega-3 fats,” says JoAnn Manson.

But not here.

Just one example is a newer study in Italy that randomly assigned about 12,500 men and women at risk of heart attacks to take either 1,000 mg of fish oil or a placebo for 5 years. The outcome: fish oil-takers were just as likely to suffer heart attacks or strokes or to die of heart disease as the placebo-takers.

Why the change?

“These trials are in people with a history of heart attack or those with a high risk of heart disease,” says Manson. “Many of them are taking statins, aspirin, ACE inhibitors, and other medications that lower their heart disease risk.”

And since some drugs work through similar pathways as fish oil, they may lower risk so much that adding fish oil to the mix doesn’t lower the risk of heart disease any further.

“The key question now is whether fish oil helps people at average risk who are not taking multiple medications for cardiovascular disease,” says Manson.

To find out, her Vitamin D and Ome­ga-3 Trial (VITAL) is giving a total of 1,000 mg a day of the two major omega-3 fats in fish oil, EPA and DHA, to 25,000 men and women with no history of heart disease or stroke. Results are due in 2017.

What should you do in the meantime?  

Follow the American Heart Association’s recommendations, says omega-3 expert William Harris of the Sanford School of Medicine at the University of South Dakota.

“People without heart disease should eat two servings of fatty fish a week, which would give them 400 to 500 milligrams of EPA plus DHA a day.” (Fatty fish include salmon, herring, mackerel, trout, and sardines.) “People with coronary heart disease should get 1,000 milligrams a day, either from fish or a pill,” says Harris.

“Even if fish oil is not as great as we thought, fish still provides nutrients like vitamin D, protein, and iron,” adds Martijn Katan, an emeritus professor of nutrition at the Vrije Universiteit Amsterdam and a world-renowned expert on diet and cardiovascular disease.


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