Harvard Heart Letter

Fish oil questioned as treatment for heart disease

It may be okay for prevention. But eating fish is a better strategy than gulping pills.

Fish oil has been flying high as a supplement for the past few years. It has garnered a reputation as an easy way to protect the heart, ease inflammation, improve mental health, and lengthen life. Such claims are one reason why Americans spend more than $1 billion a year on over-the-counter fish oil, and why food companies are adding it to milk, yogurt, cereal, chocolate, cookies, juice, and hundreds of other foods.

But as has happened with so many other supplements, fish oil may have hit its "Black Tuesday." In a two-week period at the end of November 2010, reports from four randomized controlled trials — the gold standard of medical research — showed that fish oil in one form or another didn't work any better than placebo at preventing recurring heart problems among heart attack survivors or people with atrial fibrillation. (We've summarized the results of these four trials below).

Latest fish oil trials

Omega-3s for atrial fibrillation: Men and women with occasional (paroxysmal) or continuous (persistent) atrial fibrillation (AF) took 4 grams per day of Lovaza, a prescription form of omega-3s, or a placebo for 24 weeks. Lovaza was no better than placebo at suppressing new episodes of AF among people with paroxysmal AF, and was slightly worse than placebo for preventing AF symptoms in participants with persistent AF (JAMA, Dec. 1, 2010).

SU.FOL.OM3 trial: Among survivors of a heart attack or ischemic (clot-caused) stroke, or those with unstable angina (chest pain at rest), taking 600 milligrams (mg) of omega-3s a day for almost five years was no better than placebo at reducing nonfatal heart attacks, strokes, or deaths from cardiovascular disease (BMJ, Nov. 29, 2010).

Alpha Omega trial: Daily use of a margarine made with an extra 400 mg of omega-3 oils for more than three years was no better than the same margarine minus the added omega-3 oils at preventing heart attack, stroke, the need for angioplasty or bypass surgery, or heart-related death (New England Journal of Medicine, Nov. 18, 2010).

OMEGA trial: Among heart attack survivors, 1,000 mg of purified omega-3 oils a day for one year was no better than olive oil at preventing sudden cardiac arrest, death, heart attack, stroke, or the need for bypass surgery or angioplasty (Circulation, Nov. 23, 2010).

Flip-flop on benefits

British physiologist Hugh Sinclair kindled interest in the heart-healthy properties of oily fish and fish oil in the 1940s by suggesting they helped keep the Inuit (Eskimo) people healthy in spite of their high-fat diet. Some long-term follow-up studies, such as the Nurses' Health Study, showed that people who eat one or more servings of fish a week are less likely to have heart attacks or heart rhythm problems or die from sudden cardiac arrest. A few randomized trials in the 1990s that added fish or fish oil to the diet supported this notion.

So why do the results of the latest trials tell a different story? The early trials were done before the widespread use of heart-protecting medications such as statins, ACE inhibitors, aspirin, and beta blockers. Without them, fish oil by itself could have made a difference. The use of state-of-the-art medical therapy in the four more recent trials could have drowned out any small benefit provided by fish oil.

Of course, it is also possible that the trials weren't large enough or didn't last long enough to have shown a benefit from fish oil. If that's the case, any benefit from fish oil is small.

These findings don't mean fish oil is a complete flop. It may work against heart disease if started earlier, before cholesterol or high blood pressure damages coronary arteries. It could (stress on "could") fight other types of cardiovascular disease or problems like depression. And it is a good treatment for high triglycerides. But if you already have heart disease, taking fish oil doesn't seem to do much good.

Eat fish

Medical research tends to practice what philosophers of science call reductionism — trying to understand the nature of something complex (like nutrition and health) by reducing it to the interactions of its parts. Early studies showing that eating more fruits and vegetables was good for health led to a focus on food components, such as fiber, vitamins, and antioxidants. None come close to offering the benefits of food itself. The same story appears to be playing out with fish and fish oil.

If you have heart disease, taking fish oil doesn't seem to replace eating fish, says Dr. Robert H. Eckel, past president of the American Heart Association and former member of its nutrition committee. The benefit could be due to fish oil in its natural state (in fish), something else in fish, or maybe the fact that eating fish means eating less red meat.

What if you just don't like fish? Then make sure your doctor has prescribed the best medical therapy for your condition and you are following his or her advice. That is far more important than taking fish oil.

And what about the American Heart Association's recommendation that people with documented coronary artery disease take in at least 1 gram of omega-3 fatty acids per day from oily fish or a supplement? "I think the time has come to reconsider those guidelines," says Dr. Eckel.