There’s more evidence that the vaunted reputation of fish oil is all wet: An updated Cochrane Library review finds that boosting two components of omega-3 fats – mainly through supplements such as fish oil – has little or no impact on cardiac health or overall mortality.
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“Although EPA and DHA reduce triglycerides, supplementary omega-3 fats are probably not useful for preventing or treating heart and circulatory diseases,” the researchers wrote, referring to eicosapentaenoic acid and docosahexaenoic acid, two sources of omega-3 fats in fish.
They did find signs that boosting intake of plant-based alpha-linolenic acid (ALA) “may be slightly protective for some heart and circulatory diseases.” However, they deemed the evidence to be of low quality compared with the high- to moderate-quality evidence supporting the conclusions regarding omega-3 fats from fish.
The review, led by Asmaa S. Abdelhamid, MBBCH, MSc, MD, of the University of East Anglia, was commissioned by the World Health Organization and published on July 18, 2018, in Cochrane Database of Systematic Reviews (doi: 10.1002/14651858.CD003177.pub3). It updates a 2004 Cochrane Library review.
As the review notes, “there is a great deal of public belief in the cardiovascular benefits of omega-3 fats.” But research in recent years has questioned the benefits of fish oil supplementation.
For the new review, the researchers focused on studies that boosted omega-3 fat intake using EPA, DHA and ALA.
The researchers included 79 randomized controlled trials with a total of more than 112,000 adult participants. The studies examined the cardiac and circulatory system effects of greater omega-3 consumption for at least a year compared with controls. Most trials tested supplementation with capsules, but some relied on boosting intake of foods or simply making dietary recommendations.
The studies were conducted in North America, Europe, Australia, and Asia. Researchers determined that 25 trials were designed well enough to be deemed “very trustworthy.”
According to the review’s meta-analysis, increasing intake of long-chain omega-3 fatty acids (EPA and DHA) had little to no effect on all-cause mortality (relative risk, 0.98; 39 trials), cardiovascular mortality (RR, 0.95; 25 trials), cardiovascular events (RR, 0.99; 38 trials), coronary heart disease mortality (RR, 0.93; 21 trials) and arrhythmia (RR, 0.97; 28 trials), while there was a potential boost in stroke risk (RR, 1.06; 28 trials).
The investigators noted that the relative risk of coronary heart disease events fell (RR, 0.93; 28 trials), but this did not hold up after sensitivity analysis. All these trials were deemed of moderate or high quality.
As for increased ALA intake, the researchers found little or no effect on all-cause mortality (RR, 1.01; four trials) and cardiovascular mortality (RR, 0.96; four trials) or coronary heart disease events (RR, 1.00, four trials).
Although the researchers deemed the evidence on ALA to be of low quality, there’s a possible decreased risk of cardiovascular events (RR, 0.95; five trials), coronary heart disease mortality (RR, 0.95; three trials) and arrhythmia (RR, 0.79; one trial). It’s not clear if increased ALA intake affects stroke risk.
“There was no evidence that increasing LCn3 [long-chain omega-3 fatty acids] or ALA altered serious adverse events, adiposity, or lipids, although LCn3 slightly reduced triglycerides and increased HDL. ALA probably reduces HDL (high- or moderate-quality evidence),” the researchers wrote.