Abstract
A large body of evidence supports the cardioprotective effects of the long-chain omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). There is increasing interest in the independent effects of EPA and DHA in the modulation of cardiometabolic risk factors. This systematic review aims to appraise the latest available evidence of the differential effects of EPA and DHA on such risk factors. A systematic literature review was conducted up to May 2017. Randomised controlled trials were included if they met strict eligibility criteria, including EPA or DHA > 2 g/day and purity ≥ 90%. Eighteen identified articles were included, corresponding to six unique studies involving 527 participants. Both EPA and DHA lowered triglyceride concentration, with DHA having a greater triglyceride-lowering effect. Whilst total cholesterol levels were largely unchanged by EPA and DHA, DHA increased high-density lipoprotein (HDL) cholesterol concentration, particularly HDL2, and increased low-density lipoprotein (LDL) cholesterol concentration and LDL particle size. Both EPA and DHA inhibited platelet activity, whilst DHA improved vascular function and lowered heart rate and blood pressure to a greater extent than EPA. The effects of EPA and DHA on inflammatory markers and glycaemic control were inconclusive; however both lowered oxidative stress. Thus, EPA and DHA appear to have differential effects on cardiometabolic risk factors, but these need to be confirmed by larger clinical studies.
Highlights
There are a number of well-established risk factors for the development of cardiovascular disease
The remaining 39 publications were assessed in full. Of these 39 publications, 21 were rejected because of the following reasons: two studies utilised 10% of “other” long-chain omega-3 polyunsaturated fatty acids (PUFAs) present in the administered EPA or DHA [29,32–39], six studies were uncontrolled [40–45], one study was based on a single administration of EPA and DHA only [46], two studies administered EPA and DHA together [47,48], and one result was an abstract only, with no full text
Results for EPA and DHA similar, so authors reported as one group: No significant effect on blood lipids ↓ Apo B-48 (−28%, p < 0.001) ↓ Apo B-100 (−24%, p < 0.01) ↓ Chylomicron triglyceride half-lives (p < 0.05) ↓ Chylomicron particle size (p < 0.01) ↑ Pre-heparin lipoprotein lipase (p < 0.05) ↑ Margination volumes in the fasted state (p < 0.001) ↑ Margination volumes in the fed state (DHA only; p < 0.05)
Summary
There are a number of well-established risk factors for the development of cardiovascular disease. These risk factors include, but are not limited to, elevated cholesterol, low-density lipoprotein (LDL) cholesterol and triglyceride concentrations, decreased high-density lipoprotein (HDL) cholesterol concentration, small LDL particle size, high blood pressure, increased platelet activation, elevated inflammatory markers, insulin resistance, and increased oxidative stress [1]. The main constituents of oily fish responsible for conferring cardioprotection are considered to be the long-chain omega-3 polyunsaturated fatty acids (PUFAs), predominantly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3 PUFAs are found in supplements commonly called “fish oils” and are available as concentrated pharmaceutical-grade preparations [5]. RCTs have found that increased omega-3 PUFA consumption reduces all-cause mortality and cardiac and sudden death, in the secondary prevention setting [6–8]
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