Support for a cardiovascular benefit of omega-3 fatty acids, particularly eicosapentaenoic acid (EPA), has come from a new systematic review and meta-analysis of randomized trials.
The meta-analysis of 38 randomized controlled trials found that omega-3 fatty acids improved cardiovascular outcomes, with a greater reduction in cardiovascular risk in studies of EPA alone rather than of combined eicosapentaenoic plus docosahexaenoic (DHA) supplements.
The paper is published online today in the journal, EClinicalMedicine.
Senior author Deepak Bhatt, MD, Brigham and Women's Hospital, Boston, was also lead investigator of the REDUCE-IT trial, which is included in the analysis and showed a 25% relative risk reduction in major cardiovascular events with a high-dose EPA product.
But the REDUCE-IT trial has been mired in controversy, with suggestions that the benefit seen might have been exaggerated because of the use of a harmful placebo. In addition, a second large trial of high-dose omega-3 fatty acids, STRENGTH (which tested a combination EPA/DHA product) showed no benefit on cardiovascular outcomes.
Bhatt says the new meta-analysis provides "a totality of evidence" that "supports a robust and consistent benefit of EPA."
In the review, the authors conclude: "In this systematic review and meta-analysis, we noted moderate certainty of evidence favoring omega-3 fatty acids for reducing cardiovascular mortality and outcomes.... The magnitude of relative reductions was robust in EPA trials versus those of EPA+DHA, suggesting differential effects of EPA and DHA in cardiovascular risk reduction."
But commenting on the publication for theheart.org | Medscape Cardiology, Steven Nissen, MD, Cleveland Clinic, who led the STRENGTH trial, pointed out that 85% of the EPA data in the new meta-analysis came from REDUCE-IT, so the results were a "foregone conclusion."
"The purpose of a meta-analysis is to answer scientific questions when existing studies are too small to yield statistically robust results. That is not the case here," Nissen stated.
He added: "There are only two major trials of EPA and both have important flaws. REDUCE-IT used a questionable placebo (mineral oil) and JELIS was an open-label trial that studied patients with baseline LDL-C of 180 mg/dL that was not appropriately treated. A meta-analysis is only as good as the studies that it includes. The other EPA plus DHA studies were essentially neutral."
Bhatt responded to theheart.org | Medscape Cardiology that: "To date, every randomized trial of EPA-only has been positive. Some have been placebo-controlled, some have been open-label. This meta-analysis corroborates the results of each of those trials in a statistically robust way."
He added: "Of course, REDUCE-IT is the most rigorous, contemporary trial of EPA. However, in our meta-analysis, even when excluding REDUCE-IT (or for that matter, JELIS), the EPA trials still significantly reduced cardiovascular events."
"Beyond the clinical trial data, there is a growing amount of evidence supporting the unique biological actions of different omega-3 fatty acids. EPA, in particular, appears to have the strongest basic science evidence supporting cardiovascular benefits. Overall, it is a remarkably consistent scientific story in support of EPA's beneficial effects on cardiovascular health," he stated.
38 Trials Included
For the current paper, Bhatt and his coauthors performed a comprehensive literature search for randomized trials comparing omega-3 fatty acids to control (placebo, no supplementation, or lower dose of omega-3 fatty acids) in adults, with a follow-up of at least 12 months, and mortality and cardiovascular outcomes as endpoints.
Ultimately, 38 trials encompassing 149,051 patients were included. Of these, four trials compared EPA with control, 34 trials compared EPA+DHA with control, and 22 trials were in primary prevention. The dose of omega-3 fatty acids ranged from 0.4 g/day to 5.5 g/day.
A total of 25 trials with 143,514 individuals reported 5550 events of cardiovascular mortality, and 24 trials with 140,983 individuals reported 10,795 events of all-cause mortality.
Omega-3 fatty acids were associated with reduced cardiovascular mortality (rate ratio [RR], 0.93; P = .01), but not all-cause mortality (RR, 0.97; P = .27).
Meta-analysis showed reduction in cardiovascular mortality with EPA monotherapy (RR, 0.82; P = .04) and EPA+DHA combination (RR, 0.94; P = .02).
A total of 20 trials with 125,611 individuals reported 2989 nonfatal myocardial infarction (MI) events, and 29 trials with 144,384 individuals reported 9153 coronary heart disease (CHD) events.
Omega-3 fatty acids were associated with reducing nonfatal MI (RR, 0.87; P = .0001) and CHD (RR, 0.91; P = .0002).
Meta-analysis showed higher risk reductions in nonfatal MI with EPA monotherapy (RR, 0.72; P = .00002) than with EPA+DHA combination (RR, 0.92; P = .05), and also for CHD events with EPA monotherapy (RR, 0.73; P = .00004) than with EPA+DHA combination (RR, 0.94; P = .01).
A total of 17 trials (n = 135,019) reported 13,234 events of MACE, and 13 trials (n = 117,890) reported 7416 events of revascularization.
Omega-3 fatty acids were associated with reducing MACE (RR, 0.95; P = .002) and revascularization (RR, 0.91; P = .0001).
Meta-analysis showed higher risk reductions in MACE with EPA monotherapy (RR, 0.78; P = .00000001), whereas EPA+DHA combination did not reduce MACE (RR, 0.99; P = .48). This effect was consistent for revascularization.
A total of eight trials with 65,404 individuals reported 935 nonfatal strokes, and eight trials with 51,336 individuals reported 1572 events of atrial fibrillation (AF).
Omega-3 fatty acids did not significantly reduce nonfatal stroke (RR, 1.04; P = .55), but EPA monotherapy was associated with a reduction of nonfatal stroke, compared with control (RR: 0.71; P = .01).
Conversely, omega-3 fatty acids were associated with increased risk for AF (RR, 1.26; P = .004), with a higher risk with EPA monotherapy than with control (RR, 1.35; P = .004).
Overall, omega-3 fatty acids did not prevent sudden cardiac death or increase gastrointestinal-related adverse events, total bleeding, or major or minor bleeding; however, the meta-analysis showed a higher risk of total bleeding with EPA monotherapy than with control (RR, 1.49; P = .006).
An influence analysis with stepwise exclusion of one trial at a time, including REDUCE-IT, did not alter the overall summary estimates. "Despite the exclusion of REDUCE-IT, EPA monotherapy reduced MACE by 23% compared with the control," the authors report.
They say these new findings also have important implications for clinical practice and treatment guidelines.
"After REDUCE-IT, several national and international guidelines endorsed EPA in their therapeutic recommendations. However, the publication of two recent negative trials of EPA + DHA has created some confusion in the scientific community about the value of omega-3 FAs in preventing atherosclerotic cardiovascular disease (ASCVD)," they state.
"This meta-analysis provides reassurance about the role of omega-3 fatty acids, specifically EPA, in the current treatment framework of ASCVD residual cardiovascular risk reduction and encourages investigators to explore further the cardiovascular effects of EPA across different clinical settings," they add.
REDUCE-IT was sponsored by Amarin. Brigham and Women's Hospital receives research funding from Amarin for the work Bhatt did as the trial chair and as the international principal investigator. The present analysis was unfunded.
EClinicalMedicine. Published online July 8, 2021. Full text
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