Although eating fish confers some health benefits, a growing body of evidence suggests there's less support for the value of fish oil supplements.

Oily fish such as salmon, trout and herring are excellent sources of omega-3 fatty acids, which are associated with protective effects on the heart.

Early findings pointing to benefits of omega-3 supplements haven't panned out in clinical trials. (iStock)

Years of research studies have tested whether omega-3 fatty acid supplements such as fish oil are also beneficial.

This week, researchers who looked at heart surgery patients who took fish oil supplements before and after the procedure said that taking the supplements didn't seem to help patients heal better.

Investigators in the U.S. randomly assigned 1,516 patients scheduled for cardiac surgery in the U.S., Italy and Argentina to take one-gram capsules containing omega-3 fatty acids or a placebo of olive oil before and after their procedure, such as valve replacement.

They hoped to reduce post-operative atrial fibrillation or flutter (AF), an irregular heartbeat that occurs in about one in three patients undergoing cardiac surgery.

"Our findings provide no evidence that short-term omega-3-[polyunsaturated fatty acids] supplementation provides clinically relevant antiarrhythmic effects in the acute setting of cardiac surgery," Dr. Dariush Mozaffarian of the Harvard School of Public Health in Boston and his co-authors concluded in the Journal of the American Medical Association.

Participants took fish oil capsules containing at least 840 millligrams of long-chain omega-3 polyunsaturated fatty acids (PUFAs), a prescription strength of the supplements.

Fish versus supplements

The total number of days in the intensive care unit or coronary care unit were about the same in both groups.

The study is the latest to question the benefits of supplements and fortification, an industry worth an estimated $25 billion globally in 2011.

"It may be something else that's in the fish that's providing the benefits because fish have all sorts of minerals and other ingredients that are healthy," said Dr. Andreas Wielgosz, a cardiologist in Ottawa and a spokesperson for the Heart and Stroke Foundation.

"It may be that when you eat fish you eat less saturated foods. The exact answer isn't known but what we can say is natural source is better than supplements."

Two other research papers earlier this year found the supplements don't reduce heart attacks or strokes in people at high risk for them, and they don't prevent cognitive decline or dementia in healthy older people.

Although the initial study on the heart benefits of fish oil capsules in the late 1990s showed a reduction of 45 per cent in sudden cardiac death, use of medications like statins has increased dramatically since then, said Ken Stark, a professor of applied health sciences at the University of Waterloo who studies the metabolism of polyunsaturated fatty acids.

The use of medications could be masking benefits conferred by omega-3.

"This isn't to say omega-3s aren't working,” said Stark.

People tend not to keep taking the supplements, based on their blood levels, and the dosages have been lowered over the last 20 years, he added.

"We're suddenly giving 500 milligrams in some of these clinical studies when the Japanese are eating two grams per day."

Stark's laboratory research suggests that anti-inflammatory properties of omega-3s could help treat or prevent arthritis or eye disease, although those ideas haven't been tested in high-quality trials.

Fish oil flip

Dr. Hertzel Gerstein of the Population Health Research Institute at McMaster University in Hamilton cautions there could be an indirect harm from taking supplements instead of medications such as statins or lowering blood pressure.

"If people are taking a medication for which there is no good evidence … [and] they’re not taking proven medications, then that actually can put them at harm."

When omega-3 supplements were actually tested in clinical trials, they didn't pan out, Gerstein said.

For the most part, omega-3 supplements don't cause side-effects, though some people complain of a fishy smell or nausea from taking high doses, Gerstein added.

Janet Torge of Montreal used to spend $250 a month on supplements recommended by a naturopath. Torge recalled reading that omega-3s were supposed to help prevent dementia, so she added the supplements to her regimen. But later she gave up supplements in favour of watching what she eats more closely.

"I think the lesson is that you go with healthy living, like the basics," said Torge.

Gerry Harrington is director of public affairs for Consumer Health Products Canada in Ottawa, which represents the makers, marketers and distributors of vitamins, diet supplements and other health products.

"I think the challenge is for people to be able to take each individual study into context and realize that it's an ongoing process and the miracle vitamin one year may be much less attractive next year," said Harrington.

Harrington acknowledged contradictory research findings are confusing and frustrating for people who are trying to make healthy choices. He suggested that people talk to their pharmacist before taking supplements.

With files from CBC's Kelly Crowe and Marijka Hurko