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Fish Oil Supplements: A Fish Tale or a Good Catch?

What Is Fish Oil?

Doctors and scientists first took notice of fish oil when research revealed that cultures that ate more fish — Scandinavians and Inuits, for example — had lower rates of heart disease. Many types of fish, including  salmon, mackerel, herring, lake trout, sardines, and albacore tuna, contain omega-3 fatty acids — a healthy type of fat. Two of the most important omega-3s in fish are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Researchers wanted to know whether taking fish oil straight — without eating fish — might help the heart.

“In clinical trials, the results are very mixed,” says J.L. Mehta, MD, PhD, a cardiologist and professor at the University of Arkansas for Medical Sciences in Little Rock. “Some show benefits. Many do not.”

Why the Mixed Reviews?

Early tests showed that fish oil helped the heart in many ways, but researchers have scratched their heads when more recent studies didn’t get the same results.

“This may be because there are so many medications that are now being used to treat high-risk patients. A very large percentage are on aspirins, statins, beta-blockers, ACE inhibitors, and this may obscure the role of a dietary supplement like omega-3s,” says JoAnn Manson, MD, chief of preventive medicine at Brigham and Women’s Hospital in Boston.

It may also be that Westerners eat more fish today than they once did because they’ve heard it’s good for them, so a supplement wouldn’t help.

Different studies also use different fish oil doses and formulations — whether they are equal parts EPA and DHA or heavier on one than the other.

The Evidence for Fish Oil

If you’ve already had a heart attack or are at a high risk of having one …

Large prescription-strength doses of pure EPA — not the type you buy off the shelf at the drugstore — can help the hearts of people who have certain conditions that make heart problems more likely. Prescription fish oils lower triglycerides — a type of fat that circulates in the bloodstream. A recent study showed that 4 grams of pure EPA per day for 5 years significantly cut the risk for heart attack, stroke, bypass, chest pain, and death from sudden cardiac arrest during that time.

Omega-3 Supplements: Benefits, Risks, Side Effects

Omega-3 fatty acids are good for your brain and heart, but supplements may come with side effects.


But it’s worth noting that the people who saw these benefits already had a host of heart-related health problems. Their LDL, or “bad,” cholesterol and triglycerides were high even though they took cholesterol-lowering medications. They also already had heart disease, or they had diabetes and at least one other thing that made heart disease more likely.

For people who’ve never had a heart attack and run a normal risk of ever having one, says Manson, “it’s unlikely that 4 grams a day would be recommended. There’s a threshold at which you’d stop seeing benefits.”

A similar study found that a prescription form of 1.8 grams of EPA per day, in addition to a cholesterol-lowering medication, cut the odds of having heart attacks and other heart problems in people who had high cholesterol. Many of them also had heart disease, diabetes, and/or high blood pressure. Although 1.8 grams is a lot less EPA than 4 grams,  the study participants, who were Japanese, already got more fish oil directly from the fish in their regular diet than Westerners do.

So, exactly how much is 1.8 grams of EPA? Remember the cereal commercial that said “You’d have to eat four bowls of Raisin Bran to get the vitamin nutrition in one bowl of Total?” Well, you’d have to take 10 capsules — five servings — of an average over-the-counter fish oil supplement to get 1.8 grams of EPA. Want the full four grams? You’ll need to take about 22 capsules. And no one is recommending that. Studies that show benefits of high doses of EPA use prescription-grade pure EPA. Over-the-counter supplements have other ingredients, too, and they are not regulated and safety-tested like FDA-approved prescription drugs.

“Some people take multiple, multiple capsules. But we don’t know that that’s safe,” says Manson. “Unless that’s under the guidance of a clinician, avoid mega-dosing.”

If your heart’s already pretty healthy …

In lower doses, fish oil may help the hearts of people who are in pretty good health.  In a study of 25,871 adults over 50 with an average risk for heart attack, the ones who took 1 gram of fish oil — containing 460 mg EPA and 380 mg DHA (just a little more than you might find in a daily OTC dose) — every day for 5 years had a 28% lower risk for heart attack during that time. But they didn’t have a lower risk of stroke or death from heart disease. In fact, many studies that aimed to prove ordinary fish oil supplements lower risk for heart disease have failed to do so.

If it’s not your heart you’re worried about …

Aside from heart health, researchers have studied the effects of fish oil on many other conditions. But the benefits are clear in only a few of them. Fish oil might relieve symptoms of rheumatoid arthritis and lessen the need for pain medications, but only a little, the research shows. And in people who have a higher than average risk of getting Alzheimer’s disease because they carry the APOE ε4 gene mutation, high doses of DHA before symptoms of the disease arise may make having the condition less likely.

As for other conditions, the benefits of fish oil are either nonexistent or unclear.

Can’t I Just Eat Fish?

Absolutely. The best way to get most any nutrients, including omega-3s, is from your diet. In fact, several studies that show no benefits of fish oil supplements do show benefits of eating fish. For example, while fish oil supplements don’t lower the risk of heart disease, studies show that people who eat fish one to four times a week are less likely to die of heart disease than those who rarely or never do. Eating fish and shellfish may cut risk for stroke and for the loss of memory and thinking skills that can lead to  dementia.

What’s more, in studies that do show benefits of fish oil supplements, those benefits may be less in people who already eat plenty of fish and more in people who don’t get enough fish.

“If there’s a rock-solid reason to supplement, then it’s to fulfill nutrient shortfalls for people who don’t consume enough fish,” says Duffy MacKay, ND, who is senior vice president for scientific & regulatory affairs at the Council for Responsible Nutrition, a trade association that represents dietary supplement manufacturers and ingredient suppliers.

For example, take the study that showed that 1 gram of fish oil per day lowered the risk for heart attacks. That was true only for people who didn’t already eat fish. The researchers divided the study participants into two groups — those who ate less than a serving and a half of fish per week, and those who ate that much or more. The ones who ate the least fish had a 19% drop in heart attack, stroke, and heart disease death, and a 40% drop in heart attack risk when they took the supplement.

“They didn’t already have sufficient fish intake and weren’t already at a threshold where the supplements would have no additional benefit. If they were above 1.5 servings a week, they did not have a clear benefit,” Manson says.

What’s the Bottom Line for Over-the-Counter Fish Oil?

“Fish oil is not a magic cure-all, but the fact that the evidence is solid in a couple areas shows it is an important nutrient,” says MacKay.

If you’re already taking fish oil at a recommended over-the-counter dose, and you’re doing well on it, there’s no research that says you should stop. But don’t take any more than that. There’s no proof that’s safe or helpful.

If you’re not taking fish oil, try to get it from your plate first. The American Heart Association recommends two servings — that’s about 7 ounces — of fish a week. Preferably the fatty kind that’s rich in omega-3s.

If you want to start taking fish oil, talk to your doctor about side effects and any interactions it might have with medications you already take. The most common side effects, which 1% to 10% of people have, include belching, indigestion, nausea, bloating, belly pain, constipation, diarrhea, gas, acid reflux, and vomiting. If you take blood thinners, blood pressure-lowering medications, contraceptives, the weight loss drug orlistat (sold as Alli and Xenical), or vitamin E, talk to your doctor about interactions that could be dangerous before starting fish oil.