Should You Be Taking Fish Oil?

In the early 1970s, two Danish investigators noted that despite the high-fat diet of Greenland Eskimos, they rarely experienced heart attacks.

At that time, Jorn Dyerburg and H.O. Bang speculated that there might be a relationship between the low incidence of heart attacks and the particular type of fat in the Eskimo diet — fat of marine origin high in a specific type of polyunsaturated fat generally referred to as omega-3 fatty acids.

These fatty acids are commonly found in cold water fish such as salmon, mackerel and swordfish, but are also found in certain vegetable oils (canola oil and flax oil in particular) and nuts such as walnuts.

Omega-3 fatty acids have since been intensively investigated, and all of the accumulating evidence suggests that they have a potent effect to reduce death rates from coronary heart disease, and in particular, to prevent sudden death.

Growing Body of Evidence

This week three articles appear in the medical literature that add substantially to this evidence.

The first article, published in the Journal of the American Medical Association, reports on the association between fish consumption and total omega-3 fatty acid intake and the likelihood of developing coronary heart disease as seen in the Nurses' Health Study, a large follow-up study of 98,462 women.

The results showed that there was a clear relationship between dietary intake of fish and omega-3 fatty acids and the likelihood of developing coronary heart disease — the higher the omega-3 fatty acid intake, the lower the likelihood of coronary heart disease. This relationship was even stronger for coronary deaths.

The second article, published in the New England Journal of Medicine, looked at omega-3 fatty acid levels in blood stored from men who up to 17 years previously had entered the Physicians' Health Study, which followed 22,000 middle-aged male physicians.

This study looked directly at omega-3 fatty acid blood levels as opposed to diet. The investigators found a striking relationship between the blood level of omega-3 fatty acids present when these men entered the study and the follow-up likelihood of dying from coronary heart disease.

In particular, a high blood level of omega-3 fatty acid seemed to provide significant protection against sudden death.

Finally, the third article, published in Circulation, describes a large Italian study in which 11,000 men and women who had previously suffered a heart attack less than three months before were divided into three groups: those receiving usual care, vitamin E supplementation, and a single fish oil capsule (the equivalent of two to three American capsules).

The vitamin E did nothing to alter risk of heart disease — this is the third, large-scale study to come to this conclusion.

The fish oil capsule, on the other hand, was associated with a 45 percent reduction in sudden cardiac death.

These studies, while important, do not come out of the blue. An extraordinary series of studies has documented the value of omega-3 fatty acids, particularly as derived from fish oil, taken either as food or as fish oil supplements.

What have we learned:

1. The primary effect of omega-3 fatty acids is to reduce death rates from coronary heart disease and particularly to reduce the likelihood of sudden death.

2. This effect is not related to a change in blood cholesterol levels.

3. The favorable effect is seen very rapidly, usually by three months into the study. This contrasts with most studies of statins, the most widely used class of drug for lowering cholesterol levels, where the favorable effect on death rates is not usually seen until after a year or more of therapy. It is almost certain that omega-3 fatty acids provide benefit by a mechanism completely different from that of traditional cholesterol-lowering drugs, and it is likely that combination of the two will provide greater benefit than either alone.

4. The dose of omega-3 fatty acids needed to provide these benefits is small, the equivalent of two fatty fish meals a week. In capsule form, a total dose of 800 milligrams to 1,000 milligrams of omega-3 fatty acids per day should be sufficient. Capsules in the United States contain either 300 milligrams or 500 milligrams of omega-3 fatty acids per capsule.

5. As compared to traditional drug therapy, omega-3 fatty acids provide remarkable benefits, are entirely safe, and are inexpensive.

Should you take omega-3 fatty acids?

All of the evidence suggests that all patients with known heart or other vascular disease would benefit from taking omega-3 fatty acids, either as a cold water fish meal at least twice a week or as a supplement.

It is also likely that patients without known heart disease but who are at high risk because of factors such as elevated cholesterol, high blood pressure or diabetes also would benefit from this approach. Even individuals who are not at increased risk can reduce their risk of death from heart attack by substituting fish for meat high in saturated fat.

However, if you have had a stroke you should discuss the use of omega-3 supplements with your physician — some strokes are caused by bleeding into the brain, and omega-3 supplements, because they cause a slight increase in the likelihood of bleeding, should not be used in this situation.

Why hasn't my doctor told me this?

It is not clear why most physicians have not picked up on the very strong evidence that was already available before this week's studies.

Why physicians were so quick to recommend agents such as vitamin E — which never had very strong evidence backing its use and which has now had several negative studies — and at the same time were reluctant to recommend omega-3 fatty acids when the data favoring their use has been so strong is a mystery.

It is to be hoped that more physicians will now recommend these effective, safe, and inexpensive agents. Ockene is the David and Barbara Milliken professor of preventive cardiology, the director of the Preventive Cardiology Program, and the associate director of the division of cardiovascular medicine at the University of Massachusetts Medical School.