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Scant evidence that omega 3 supplements curb cardiovascular disease risk

Cochrane review casts doubt on popular belief about protective effects of over-the-counter remedy

Caroline White

Wednesday, 18 July 2018

There is little or no evidence that omega 3 supplements can curb the risk of cardiovascular disease, or death, concludes a Cochrane systematic review* published today.

Omega 3 fats are readily available as over-the-counter supplements and widely promoted and used because of the popular belief that these fats will protect against heart disease.

The main types of omega 3 fatty acids are alphalinolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is normally found in fats from plant foods, such as nuts and seeds, while EPA and DHA are naturally found in fatty fish, such as salmon and fish oils, including cod liver oil.

The review combines the results of 79 randomised trials involving 112,059 people, some healthy and others with existing illnesses, from North America, Europe, Australia and Asia.

The participants were randomly assigned to increase their omega 3 fat consumption or to maintain their usual intake of fat for at least a year to see what impact this might have on their risks of circulatory and heart diseases.

Most studies looked at the impact of giving a long-chain omega 3 supplement in a capsule form and compared it to a placebo. Only a few assessed whole fish intake.

Most ALA trials gave enriched foods, such as margarine, or naturally ALA-rich foods, such as walnuts, to people in the intervention groups, and non-enriched foods to other participants.

The analysis showed that increasing long-chain omega 3 provides little if any benefit on most of the studied outcomes. They found strong evidence that long-chain omega 3 fats had little or no meaningful effect on the risk of death from any cause, which was just under 9 per cent in people who had increased their intake, compared with 9 per cent in those who hadn’t.

And taking more long-chain omega 3 fats (including EPA and DHA), primarily through supplements probably makes little or no difference to the risk of cardiovascular disease, heart attack, stroke, heart irregularities, or death from coronary artery disease, the review found.

Long-chain omega 3 fats probably does lower triglycerides and HDL cholesterol: educing triglycerides is likely to protect against heart disease, but lowering HDL has the opposite effect.

The systematic review suggests that eating more ALA through food or supplements probably has little or no effect on the risk of dying from cardiovascular disease or deaths from any cause. But upping ALA intake probably reduces the risk of heart irregularities from 3.3 per cent to 2.6 per cent.

But reductions in cardiovascular disease “events” through increased ALA consumption were so small that around 1000 people would need to up their intake for one of them to benefit. Similar results were found for cardiovascular death. There were insufficient data from the studies to measure the risk of bleeding or blood clots associated with ALA use.

Lead Cochrane review author, Dr Lee Hooper, of the University of East Anglia, said: “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. This large systematic review included information from many thousands of people over long periods. Despite all this information, we don’t see protective effects.”

He continued: “The review provides good evidence 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. 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.

“This systematic review did find moderate evidence that ALA, found in plant oils (such as rapeseed or canola oil) and nuts (particularly walnuts) may be slightly protective of some diseases of the heart and circulation. However, the effect is very small: 143 people would need to increase their ALA intake to prevent one person developing arrhythmia. One thousand people would need to increase their ALA intake to prevent one person dying of coronary heart disease or experiencing a cardiovascular event.”

He added: “ALA is an essential fatty acid, an important part of a balanced diet, and increasing intakes may be slightly beneficial for prevention or treatment of cardiovascular disease.”

*Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega 3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 5. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub3.

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