A systematic review of evidence on omega 3 supplements has challenged the belief that they reduce the risk of heart disease, stroke, or death.
The new Cochrane review1 combined the results of 79 randomised trials involving 112 059 people and assessed the effects of consuming additional omega 3 fat, compared with usual or lower omega 3, on diseases of the heart and circulation. Some of the participants were healthy while others had existing conditions.
Twenty five studies were assessed as highly trustworthy because they were well designed and conducted. These covered the three main types of omega 3 fatty acids: alphalinolenic acid (ALA), which is normally found in fats from plant foods, such as nuts and seeds; and eicosapentaenoic acid and docosahexaenoic acid, collectively called long chain omega 3 fats, which are naturally found in fatty fish, such as salmon, and fish oils including cod liver oil.
The review suggested that increasing intake of long chain omega 3 provides little, if any, benefit on most outcomes.
It found “high certainty evidence” that long chain omega 3 fats had little or no meaningful effect on the risk of death from any cause, which was 8.8% in people who had increased their intake of omega 3 fats, compared with 9% in people in the control groups.
It also found that taking more long chain omega 3 fats primarily through supplements probably makes little or no difference to risk of cardiovascular events, coronary heart deaths, coronary heart disease events, stroke, or heart irregularities.
In terms of consuming more ALA through food or supplements, the review found it probably has little or no effect on cardiovascular deaths or death from any cause, reducing the risk of heart irregularities from 3.3% to 2.6%.
The review team found that reductions in cardiovascular events with ALA were so small that about 1000 people would need to increase consumption of the fat for one of them to benefit. Similar results were found for cardiovascular death.
They did not find enough data from the studies to be able to measure the risk of bleeding or blood clots from using ALA.
Cochrane lead author Lee Hooper from 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.”
Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, said that the review had a “major limitation” in that it has been unable to allow for the increased intakes of omega 3 fatty acids over the past 20 years because of changes in food production.
He added that most of the trials reviewed were in patients with pre-existing cardiovascular disease, which was a further limitation when extrapolating to the prevention of heart attacks in the general population.
“The data from previous observational cohort studies, which this review doesn’t take into account, suggest a threshold intake where intakes below 1g/d of ALA are associated with increased risk of fatal heart disease. It follows, therefore, that intakes above this level are unlikely to have any further benefit. Because a small amount of an essential nutrient is needed, it does not follow that more is always better,” he said.
Sanders added that the study provided no evidence that current dietary advice to eat two portions of fish a week, one of them oily, should change.