More specifically, omega-3 fatty acids are of three main types: alphalinolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).
ALA is an essential fatty acid, which means that the human body cannot produce it on its own and has to get it from food.
Flaxseed, soybean, and canola oils, as well as chia seeds and walnuts, all contain ALA.
DHA and EPA — also called long-chain omega-3s — can both be found in fatty fish such as salmon, mackerel, tuna, herring, and sardines, as well as in other kinds of seafood.
Studies have shown that those who consume fish regularly as part of a healthful, balanced diet are at a lower risk of heart problems. But the National Institutes of Health (NIH) explain that research is unclear as to whether these benefits come from fish or omega-3 in particular.
While the jury is still out on the matter, millions of people in the United States have turned to omega-3, or fish oil supplements, due to their alleged heart health benefits.
In fact, as a survey carried out by the NIH reports, "Fish oil was the most popular natural product used by adults in the United States in 2012," with about 18.8 million U.S. individuals taking it.
But are the supplements actually worth the hype? A new review by researchers at Cochrane, an independent organization that evaluates existing medical research, assesses the benefits of the supplements by looking at the evidence available.
Lee Hooper, the lead author of the meta-analysis, is an expert systematic reviewer and reader in research synthesis, nutrition, and hydration from the Norwich Medical School at the University of East Anglia in the United Kingdom
The findings are now published in the Cochrane Library.
Reviewing almost 80 clinical trials
Hooper and colleagues reviewed 79 randomized trials, summing up 112,059 participants. The trials assessed the cardiovascular effects of taking omega-3 supplements and compared them with those of normal or lower intake of omega-3.
In most studies, some participants were given fish oil supplements, while others took placebos.
Other studies had prompted participants to increase their omega-3 intake over the course of 1 year, while other participants were asked to keep it the same.
The majority of the trials that assessed the effect of ALA intake gave participants in the intervention group omega-3-enriched foods such as margarine, or foods naturally rich in ALA, including walnuts. The control group had a normal, non-enriched diet.
Supplements have 'little or no effect'
The review found that taking long-chain omega-3 supplements had "little or no effect" on death risk from any causes, death risk from cardiovascular problems, or death risk from coronary heart disease.
The supplements are also reported to have had "little or no effect" on the risk of cardiovascular events, stroke, or irregular heartbeat.
As for ALA, increasing intake from walnuts or fortified products such as margarine "probably makes little or no difference to all-cause or cardiovascular deaths or coronary events but probably slightly reduce[s] cardiovascular events, coronary mortality, and heart irregularities," the authors conclude.
However, this reduction is so slight that 1,000 people would have to increase their ALA intake in order for one of them to benefit, say the researchers.
This is based on "moderate- and high-quality evidence." Conversely, "Previous suggestions of benefits from EPA and DHA supplements appear to spring from trials with higher risk of bias," write the authors.
Finally, the effects of ALA on stroke risk remain unclear because the evidence was considered to be "of very low quality."
Diet may help, but supplements do not
Hooper comments on the results, saying, "We can be confident in the findings of this review which go against the popular belief that long-chain omega-3 supplements protect the heart."
"The review provides good evidence," she adds, "that taking long-chain omega-3 (fish oil, EPA, or DHA) supplements does not benefit heart health or reduce our risk of stroke or death from any cause."
"The most trustworthy studies consistently showed little or no effect of long-chain omega-3 fats on cardiovascular health," Hooper emphasizes. "On the other hand, while oily fish is a healthy food, it is unclear from the small number of trials whether eating more oily fish is protective of our hearts."
In an expert reaction to the review, Tim Chico — who is a professor of cardiovascular medicine and an honorary consultant cardiologist at the University of Sheffield in the U.K. — says, "Although diet plays an important role in preventing heart disease, this is complex and unlikely to relate much to any single element of the diet."
"Previous experience has shown that although some types of diet are linked to lower risk of heart disease, when we try to identify the beneficial element of the diet and give it as a supplement it generally has little or no benefit."
Prof. Tim Chico