Fish Oil Capsules: Net Benefits for the Heart are Limited

Every day, millions of people swallow fish oil capsules, many of them lured by the promise that the pills will help them cast off heart disease. In fact, the label of one popular brand includes the line, “May reduce coronary heart disease risk.”

Don’t take the bait: these bold marketing claims haven’t caught up with the latest science. Earlier this year, the American Heart Association (AHA) issued an updated advisory about fish oil supplements and their cardiovascular benefits. Their verdict: fish oil supplements may slightly lower the risk of dying of heart failure or after a recent heart attack. But they do not prevent heart disease.

“It’s probably not wise for any middle-aged person to start taking fish oil supplements without the advice of a physician,” says Dr. Eric Rimm, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health. Even for people who do have heart disease, the potential benefits are quite modest, he notes. If you’ve had a heart attack, taking about a gram (1,000 mg) of fish oil per day may lower your risk of sudden cardiac death by about 10%. In people with heart failure, fish oil supplements may reduce death and hospitalizations by about 9%.

The AHA’s earlier recommendation, published in 2002, advised people with known heart disease to consume about a gram per day of the omega-3 fatty acids DHA and EPA, ideally from eating fatty fish. But people could also consider omega-3 fatty acid supplements in consultation with a physician.

The early evidence for fish oil supplements looked promising. But over the past 15 years, many trials have compared them with placebos. There is no evidence that taking fish oil supplements offers any benefit for people prone to cardiovascular disease, including those with diabetes, atrial fibrillation, or stroke.

Even so, some people — including those who aren’t in that small group who might benefit from the supplement — may be tempted to keep taking fish oil. They figure that it can’t hurt and just might help. But that’s not necessarily true, says Dr. Rimm. Although “there’s still good evidence that eating fish twice a week may help lower heart disease risk,” he says, the concentrated oil found in supplements is not entirely without risk.

As is true for all dietary supplements, there is no oversight or regulation regarding the source, quality, or amount of active ingredient in these over-the-counter products. Some studies have detected trace amounts of polychlorinated biphenyls (PCBs) in some brands of fish oil supplements. Although these industrial chemicals were banned in 1979 after they were linked to cancer, they’re still found in fish exposed to water contaminated from soil runoff. Other research has revealed that some supplement brands don’t provide the amounts of DHA and EPA advertised on their labels.

It’s also worth noting that fish oil may reduce formation of blood clots. That’s potentially beneficial, but only up to a point. Too much fish oil may increase bleeding risk, particularly in people who also take anticlotting medications, including warfarin (Coumadin) and low-dose aspirin.

Many people take low-dose aspirin for heart attack prevention, Dr. Rimm points out. “Taking fish oil on top of that may not only have no benefit, it may even have some risks that we don’t realize because we haven’t studied them.”