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Ask the Doctor: What is the Upper Limit for Omega-3 Fats?

Content provided by the Faculty of the Harvard Medical School

Q. There's a lot of publicity about omega-3 fats being beneficial for heart, mind, joints, eyes, and so on. There are over-the-counter products of varying size. So, this is my question: is there a daily upper limit on fish oil consumption?

A. There isn't an official upper limit, but for most people, I'd be inclined to draw the line at a gram — 1,000 milligrams (mg) — of omega-3s from fish oil a day.

One of the main concerns about high omega-3 consumption has been that it could "thin the blood" and thus increase the risk of bleeding and, more specifically, bleeding strokes (the medical term is hemorrhagic stroke). That worry dates back to the classic studies of the Inuit people of Greenland and their traditional diet of seal and fish. Researchers observed that, along with the apparent benefits — low rates of heart disease, ischemic stroke, diabetes, and various inflammatory conditions — Inuit people had a tendency to bleed from the nose and urinary tract and had higher rates of hemorrhagic stroke.

But I don't believe we need to be overly concerned about a bleeding risk from omega-3s for several reasons. First, the Inuit people included in those studies consumed far more than a gram a day of omega-3s. Their daily intake was, on average, about 6.5 grams. Second, the Inuit studies were epidemiological studies, which point to interesting associations, but usually can't be used to prove causation. Third, research of the bleeding risk from omega-3s that has been done since has been inconclusive.

Furthermore, we now have quite a bit of experience with fairly high doses of omega-3s, and I am unaware of any significant bleeding problems. The FDA has approved a prescription fish oil, called Lovaza, at a dose of 4 grams a day as a treatment for high levels of triglycerides, fats in the blood that can contribute to atherosclerosis and heart disease. Lovaza is purified fish oil, so each 1-gram capsule contains about 900 mg of omega-3s. So 4 grams a day works out to at least 3,600 mg of omega-3s.

Large doses of omega-3s may have other therapeutic purposes. A study found that Lovaza at 4 grams a day might counteract the loss of muscle that occurs with age (sarcopenia). Other studies have suggested 1 to 2 grams a day of omega-3s from fish oil could have anti-inflammatory effects for people suffering from severe infections and recovering from surgery. And the American Heart Association has long recommended that people with known heart disease consume a gram of omega-3s from fish oil per day.

But most people don't need that level of omega-3 intake. The best evidence for omega-3s having health benefits comes from studies that have shown a protective effect against fatal heart attacks and stroke. Those benefits seem to occur at an intake that averages out at between 250 mg and 500 mg a day. For the general public, larger amounts don't appear to add to the cardiovascular protection. So the majority of us get most of the proven benefits from omega-3s by taking one fish oil capsule a day or by eating a variety of fish rich in omega-3s (salmon, for example) a couple of times a week.

It's a little confusing, because most over-the-counter fish oil is sold in 1-gram capsules, so it might seem like you are getting 1 gram of omega-3s. But read the label closely. Usually only about a third to half of the fat content consists of omega-3s, the two most common varieties of which are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The rest is other types of fat, saturated and unsaturated.

— Bruce R. Bistrian, M.D.
Beth Israel Deaconess Medical Center

Last Annual Review Date: 2011-06-01 Copyright: © 2011 Harvard Health Publications

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