EPA

Eicosapentaenoic acid is one of the two principal marine omega-3 fatty acids, alongside docosahexaenoic acid (DHA). Structurally it is a twenty-carbon chain carrying five cis double bonds, the first of which lies three carbons from the methyl (omega) end, giving the shorthand designation 20:5(n-3). The human body can make small amounts of EPA from the plant omega-3 alpha-linolenic acid, but this conversion is inefficient, so dietary intake from fish and algae is the main source. Fish themselves largely acquire EPA by eating algae rather than synthesizing it.

EPA is built into the phospholipids of cell membranes and acts as a substrate for the enzymes that generate eicosanoids, including prostaglandins, thromboxanes, and leukotrienes, as well as newer families of anti-inflammatory and inflammation-resolving mediators known as resolvins ^[2]. Because the eicosanoids formed from EPA are generally less inflammatory than those made from the omega-6 fatty acid arachidonic acid, a higher EPA intake tends to shift the body toward a less inflammatory state ^[2].

Ordinary fish-oil supplements have produced mixed results for preventing heart attacks and strokes, but a large randomized trial, REDUCE-IT, found that a high-dose purified EPA ethyl ester (icosapent ethyl) significantly reduced cardiovascular events in patients whose triglycerides remained elevated despite statin therapy ^[1]. EPA has also been studied in mood disorders; a meta-analysis of supplementation trials in major depression found a modest overall benefit that was greater for EPA-predominant formulations ^[3].

EPA is available both as a nutrient in foods and as fish-oil dietary supplements, which usually contain a mixture of EPA and DHA. In purified pharmaceutical form it is marketed as the prescription drug icosapent ethyl (Vascepa), approved as an adjunct to diet for very high triglycerides and, in some regions, to reduce cardiovascular risk ^[1]. Marine bacteria and microalgae produce EPA through dedicated biosynthetic pathways, and algal oil offers a plant-derived source for people who do not eat fish.

EPA is very safe for most people; high doses can cause a fishy aftertaste, mild GI upset, and a mild blood-thinning effect. People on anticoagulants should mention high-dose fish oil to their doctor. A purified product limits contaminant concerns.