Omega-3 Fatty Acids and Cardiovascular Disease: An Updated Systematic Review.

Abstract

The effect and association of omega-3 fatty acids (n-3 FA) intake and biomarker levels with cardiovascular (CV) clinical and intermediate outcomes remains controversial. We update prior Evidence Reports of n-3 FA and clinical and intermediate CV disease (CVD) outcomes. Evaluate the effect of n-3 FA on clinical and selected intermediate CV outcomes and the association of n-3 FA intake and biomarkers with CV outcomes. The n-3 FA under review include eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), stearidonic acid (SDA), and alphalinolenic acid (ALA). MEDLINE®, Embase®, the Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and CAB Abstracts from 2000 or 2002 to June 8, 2015, and eligible studies from the original reports and relevant existing systematic reviews. We included randomized controlled trials (RCTs) of any n-3 FA intake compared to no, lower, or other n-3 FA intake with an outcome of interest conducted in healthy adults, those at risk for CVD, or those with CVD. We also included prospective observational studies of the association between baseline n-3 FA intake or biomarker level and followup outcomes. We required 1 year or more of followup for clinical outcomes and 4 weeks for intermediate outcomes (blood pressure [BP] and lipids). From 11,440 citations (from electronic literature searches and existing systematic reviews), 829 abstracts met basic eligibility criteria; 61 RCTs and 37 longitudinal observational studies (in 147 articles) were included. Most RCTs and observational studies had few risk-of-bias concerns. The 61 RCTs mostly compared marine oil supplements with placebo on CVD outcomes in populations at risk for CVD or with CVD, while the 37 observational studies mostly examined associations between various individual n-3 FA and long-term CVD events in generally healthy populations. Compared with the prior report on n-3 FA and CVD, there is more robust RCT evidence on ALA and on clinical CV outcomes; also, by design there are newly added data on associations between n-3 FA biomarkers and CV outcomes. However, conclusions regarding the effect of n-3 FA intake on CV outcomes or associations with outcomes remain substantially unchanged. Marine oils statistically significantly raise HDL-c and LDL-c by similar amounts (≤2 mg/dL), while lowering Tg in a dose-dependent manner, particularly in individuals with elevated Tg; they have no significant effect on BP. ALA has no significant effect on intermediate outcomes. Limited data were available from RCTs on the effect of n-3 FA on clinical CVD outcomes. Observational studies suggest that higher marine oil intake (including from dietary fish) is associated with lower risk of several CVD outcomes. No clear differences in effects or associations were evident based on population, demographic features, or cointerventions. Future RCTs would be needed to establish adequate evidence of the effect of n-3 FA on CVD outcomes or to clarify differential effects in different groups of people. However, future trials are unlikely to alter conclusions about the effects of n-3 FA supplementation on intermediate cardiovascular outcomes (BP, LDL-c, HDL-c, or Tg).