About 10 percent of Americans take fish oil (omega-3) capsules, which are now the third most widely used dietary supplement after multivitamins and calcium. That’s no surprise, since over the years studies have continually linked fish or the omega-3 fats they contain with a variety of health benefits, notably a reduced risk of cardiovascular disease. The U.S. government’s Dietary Guidelines, the American Heart Association (AHA), the World Health Organization and other health groups around the world recommend eating fish regularly, preferably fatty fish such as salmon, herring and sardines.
But Americans eat, on average, only two or three ounces of seafood a week, and they often choose less-fatty types such as canned light tuna, whitefish and shrimp. Some people simply don’t like fish or don’t eat it because they’re vegetarians, or they worry about contaminants in it. Thus, many turn to fish oil supplements. The AHA gives people with heart disease the option of taking the capsules to reach the omega-3 intakes it recommends for them. Since 2004 the Food and Drug Administration (FDA) has allowed the supplements to carry a “qualified” health claim linking them to a reduced risk of heart disease, though the label has to state that the evidence is “not conclusive.”
“Not conclusive,” it turns out, is an understatement. In fact, disappointing findings from clinical trials and analyses during the past two years have called into question the proposed cardiovascular benefits of fish oil supplements. The latest setback was a large Italian study, which failed to find any benefits (see "Fish oil capsules in question," below). Is it time to deep-six your omega-3 capsules?
Omega-3s and heart health
Omega-3 fats are among the most studied nutrients for cardiovascular health. Observational studies consistently show that people who eat the most fish, especially fatty fish, are at reduced risk for heart attacks, stroke and other coronary problems. This benefit was first suggested by studies of Inuit in Greenland, who eat lots of fatty fish (and marine mammals, also rich in omega-3s) and have low rates of cardiovascular disease.
Exactly how fish reduces the risk is not clear. Research, mostly done in the lab, has found that omega-3 fats in fish oil help prevent arrhythmias (abnormal heart rhythms) and blood clots, reduce inflammation, make arteries more flexible, lower triglycerides (substantially, when taken in high doses) and reduce blood pressure (modestly). Other factors may also be involved.
The AHA advises people with heart disease to consume 1 gram (1,000 milligrams) a day of omega-3s, preferably from fatty fish. For people with very high triglycerides, it recommends 2 to 4 grams a day from supplements, under a doctor’s care. Prescription high-dose omega-3 capsules have been approved by the FDA specifically to treat very high triglyceride levels.
Some research also suggests that omega-3s may help relieve the inflammatory symptoms of rheumatoid arthritis and other autoimmune conditions, help preserve cognitive function in older people and help treat depression. The evidence for these benefits is preliminary, however. And a major 2013 study found that, contrary to expectations, supplemental omega-3s do not help prevent age-related macular degeneration.
Fish oil capsules in question
Well-designed clinical trials testing omega-3 supplements for cardiovascular health have produced inconsistent or inconclusive findings. Interestingly, while most early studies found benefits, much of the more recent research has not. Here are a few notable examples:
In 2012, two large analyses pooled data from well-designed clinical trials involving people with pre-existing heart disease or multiple risk factors. One was published in the Archives of Internal Medicine, the other in the Journal of the American Medical Association. They concluded that overall the evidence does not support claims that omega-3 supplements help prevent cardiovascular events.
Another large analysis of various studies, published last year in the British journal BMJ, looked at the link between fish consumption or omega-3 supplements and the risk of stroke. It found that the 26 observational studies suggested that higher fish intake was associated with moderately reduced stroke risk, but that the 12 clinical trials (considered the gold standard in medical research) concluded that the supplements offered no benefit.
In a large trial in the New England Journal of Medicine in 2012, people with diabetes or prediabetes, who are at elevated risk for cardiovascular disease, took 1,000 milligrams of omega-3 supplements a day or a placebo. After an average of six years, the supplement takers were no less likely to have a heart attack or stroke or to die.
A British study in the American Journal of Clinical Nutrition in 2011 found that various doses of omega-3s did not help keep arteries flexible in healthy people (ages 45 to 70). Another British study, in the journal Atherosclerosis, similarly found no vascular benefit in people with peripheral artery disease. However, a 2012 analysis in the same journal concluded that omega-3s can improve arterial functioning.
In the newest study, published in the New England Journal of Medicine in May, more than 6,000 Italians at high risk for cardiovascular disease took 1,000 milligrams of omega-3 supplements a day. After five years, they did no better than a placebo group in terms of cardiovascular death rates or hospital admissions. This was true even of people with low baseline dietary intakes of omega-3s and those not taking statins.
Critics have raised questions about some of the newer studies, saying they were not large enough to detect benefits, didn’t last long enough or used omega-3 doses that were too low. Others have criticized how the studies included in the meta-analyses were selected. Had certain other studies been included, the critics say, the overall results would have been more positive. Still, benefits that are so hard to spot are likely to be quite small.
The most salient point may be that in the studies from recent years, far more participants at elevated cardiovascular risk were taking “state-of-the-art” medication, such as statins and blood pressure drugs, compared to early studies. That helps explain the apparent lack of effect of the supplements. Even if omega-3s provide benefits, these would be hard to detect against the backdrop of the much larger benefits of these drugs. That could also make the supplements all the more unnecessary. (The same thing is seen in studies of low-dose aspirin, the benefits of which appear much smaller than previously estimated, now that so many high-risk people are taking statins.)
Bottom line: The proposed cardiovascular benefits of fish oil supplements now seem uncertain. Some major studies are underway and may help clarify matters. In any case, your best bet is to get your omega-3s from two or three servings of fatty fish a week. The AHA continues to advise people with heart disease or high triglycerides to consider taking the supplements, after consulting their doctors. That’s still good advice if you don’t eat fish, especially since some of the other proposed benefits of omega-3s may still pan out. The supplements have few, if any, serious adverse effects—unless, that is, they lead you to think you can eat an unhealthy diet or can avoid taking the statins or other drugs you may need.
Originally published May 2013. Updated March 2014.