When scientists discuss the health benefits of omega-3 fatty acids, EPA — eicosapentaenoic acid — is almost always at the centre of attention. This long-chain fatty acid is not a passive nutritional component but a biochemically highly active substance that intervenes directly in central regulatory processes of the body: inflammation control, heart rhythm, blood coagulation and even mood regulation. EPA is therefore far more than a supplement buzzword — it is one of the best-researched bioactive compounds in nutritional science. This article explains what EPA is chemically, how it works in the body, which foods contain it, how much you need daily, and how EPA differs from its sibling fatty acid DHA.

What is EPA? Chemical structure and properties

EPA stands for eicosapentaenoic acid — a name derived directly from the Greek: "eicosa" means twenty, "penta" five. This precisely describes the chemical structure of this fatty acid: a carbon chain with exactly 20 atoms and 5 double bonds. In fatty acid nomenclature, EPA is written as C20:5n-3, where n-3 (also called omega-3) indicates that the first double bond is at the third carbon atom from the methyl end of the chain.

These five double bonds, all in cis configuration, give EPA a characteristically bent, flexible molecular shape. This flexibility is biologically decisive: EPA can easily incorporate into cell membranes and influence their fluidity and function. At the same time, the high number of double bonds makes EPA susceptible to oxidation — a reason why high-quality fish oil products should contain antioxidants such as vitamin E.

The human body cannot produce EPA from scratch. The only endogenous route leads through the plant-based alpha-linolenic acid (ALA, C18:3n-3), which is gradually converted to EPA via two enzymes — delta-6-desaturase and elongase. However, this conversion is notoriously inefficient: only about 5–10% of ingested ALA is actually converted to EPA; the rest is oxidised or used as an energy source. Plant-based omega-3 sources such as linseed oil, chia seeds or walnuts can practically not meet EPA requirements — unlike oily sea fish or corresponding supplements.

Compared to DHA (C22:6n-3), which is somewhat larger with 22 carbon atoms and 6 double bonds, EPA has a more pronounced metabolic role as a precursor to bioactive signalling molecules. DHA, on the other hand, primarily assumes structural roles in brain cells and the retina. Both fatty acids complement each other but have clearly different main areas of action in the body.

Effects of EPA in the body

EPA and cardiovascular health

The cardioprotective effect of EPA is one of the best-documented properties of marine omega-3 fatty acids. The European Food Safety Authority (EFSA) has approved the health claim that EPA and DHA in an amount of 250 mg daily contribute to normal cardiac function. For higher amounts — from 2,000 mg EPA+DHA daily — the maintenance of normal triglyceride levels is also scientifically recognised.

How exactly does EPA affect the cardiovascular system? Several mechanisms work together. First, EPA influences the formation of thromboxane A2, a strongly vasoconstrictive and platelet-activating eicosanoid from the omega-6 series. EPA competes here as an alternative substrate and shifts the balance towards less aggregation-promoting signalling molecules. Second, EPA reduces the synthesis of VLDL particles in the liver, which lowers triglyceride levels in the blood. Third, EPA modulates heart rhythm stability via ion channels in cardiomyocytes.

The REDUCE-IT study (Reduction of Cardiovascular Events with Icosapent Ethyl) from 2018, published in the New England Journal of Medicine, delivered remarkable results: high-risk patients with elevated triglycerides who received 4 g of highly pure EPA ethyl ester (icosapent ethyl) daily showed a significant reduction in cardiovascular events compared to the placebo group. This study has repositioned EPA as an independent cardiovascular agent and is one of the most cited omega-3 studies of recent decades. Further information on cardiac effects can be found in the article Omega-3 and heart health.

EPA as an anti-inflammatory omega-3

EPA is the most important direct precursor of a family of inflammation-modulating signalling molecules called eicosanoids. From EPA, the cyclooxygenase and lipoxygenase enzymes produce series-3 prostaglandins and series-5 leukotrienes. These eicosanoids from the EPA series are significantly less pro-inflammatory than their counterparts from the omega-6 fatty acid arachidonic acid (AA), which forms series-2 prostaglandins and series-4 leukotrienes.

The ratio of omega-6 to omega-3 in the modern Western diet is often 15:1 to 20:1 — far from the evolutionarily adapted ratio of approximately 4:1 or lower. This shift favours a chronic low-grade inflammatory predisposition. EPA acts here as a metabolic antagonist: through its competition with arachidonic acid for the same enzymes, a sufficiently high EPA level shifts the eicosanoid balance towards less pro-inflammatory signalling.

Additionally, EPA together with DHA forms special specialised pro-resolving mediators (SPMs) — including E-series resolvins (derived from EPA) and protectins. These molecules actively resolve inflammatory processes rather than simply suppressing them. This mechanism is biochemically particularly interesting because it enables active resolution of inflammation — not just passive dampening. More on this topic in the article Omega-3 and inflammation.

EPA and mental health

One of the most surprising research directions of the last two decades concerns the connection between EPA and mental health. Several randomised controlled trials and meta-analyses have investigated whether omega-3 fatty acids — and specifically EPA — might have a supportive role in depression.

Notably, in these studies EPA-rich formulations (with an EPA to DHA ratio above 2:1) showed more consistent effects than DHA-dominant preparations. An influential meta-analysis by Sublette and colleagues (2011, Journal of Clinical Psychiatry) found that omega-3 supplementation with an EPA content of at least 60% showed statistically significant antidepressant effects. Cochrane reviews have rated these findings as moderate and pointed to methodological heterogeneity, but the evidence is considered sufficiently consistent to regard EPA as a supportive factor within a multimodal treatment approach.

The mechanisms by which EPA might influence mental health have not yet been fully elucidated. Under discussion are: modulation of serotonin release and sensitivity, dampening of neuroinflammatory processes (which are demonstrably elevated in depression), improvement of membrane fluidity in neurons, and interaction with the endocannabinoid system. This research is active and many details are still considered preliminary. Detailed information in the article Omega-3 and depression.

EPA content of important fish species

The following table shows the approximate EPA content of various fish species per 100 g edible portion. Values can vary depending on fishing area, season, farming method and preparation.

Fish species EPA (mg/100 g) DHA (mg/100 g) Note
Atlantic herring 1,000–2,000 900–1,800 Wild-caught, particularly rich
Mackerel (Atlantic) 600–1,500 1,100–2,000 Very good EPA/DHA ratio
Wild salmon (Pacific) 500–1,200 700–1,500 Wild > farmed for EPA
Sardines (Atlantic) 800–1,500 700–1,200 Small but EPA-rich
Tuna (bluefin) 200–700 900–1,800 DHA emphasis
Rainbow trout 200–600 400–900 Depends on feed

In general: the fattier the fish and the colder the water, the higher the EPA content. Wild-caught Atlantic herring is therefore one of the best natural EPA sources.

EPA sources: fish, fish oil and algae oil

Oily sea fish — the most natural EPA source

The most traditional way to obtain EPA is regular consumption of oily sea fish. Nutritional authorities typically recommend at least one to two portions of oily fish per week — an amount with which one can easily reach the minimum recommendation of 250 mg EPA+DHA daily.

When buying fish it is worth paying attention to the origin. Wild-caught herring, mackerel and salmon from the North Atlantic generally have higher omega-3 contents than farmed fish raised on more grain-based feed. However, farmed salmon fed with omega-3-enriched feeds can also provide considerable EPA values. Tinned sardines are an inexpensive and practical EPA source, as the canning process barely affects the fatty acids.

Eating fish twice weekly is sufficient for many people to cover basic requirements. However, those seeking therapeutically higher amounts — for example to support normal triglyceride levels — will struggle to reach the required 2,000 mg of EPA+DHA daily from fish alone. This is where supplements come in.

Fish oil supplements: concentration and quality

Fish oil capsules and liquids are the most widespread form of omega-3 supplementation. However, the quality differences between various products are considerable. What matters is the actual EPA+DHA content per capsule — not the total fish oil weight. A typical standard fish oil capsule contains 1,000 mg of fish oil, but often only 180 mg EPA and 120 mg DHA. For therapeutic amounts, correspondingly concentrated products are needed.

High-quality fish oils use the triglyceride or re-esterified triglyceride form (rTG), which offer better bioavailability than the cheaper ethyl ester form (EE). Good products should also have a low TOTOX value (a measure of oxidation), which indicates fresh, carefully processed raw material. Information on quality criteria can be found in the buying guide for omega-3 oils.

Algae oil: EPA from vegan source

An important detail many people do not know: fish do not produce EPA and DHA themselves. They accumulate the fatty acids by eating marine microalgae — directly or through the food chain. The true "inventors" of EPA and DHA are therefore microalgae and certain marine fungi.

Algae oil supplements use this original source directly. They are derived from cultivated microalgae species such as Schizochytrium or Nannochloropsis, which produce EPA and/or DHA. For vegans and vegetarians, algae oil is the only reliable direct source of these fatty acids without an animal intermediary.

Older algae oil products were heavily DHA-dominant and contained little EPA. Newer product lines from certain algae species, however, increasingly deliver relevant amounts of EPA. Those seeking vegan EPA supplementation should carefully compare the nutritional information of products and specifically look for EPA-containing algae oils.

EPA dosage: how much is sensible?

The optimal EPA dosage depends on the individual goal. EFSA has defined clear health claim amounts that can serve as guidance. For healthy adults without specific risk factors, the general recommendation of 250 mg of EPA+DHA daily is considered sufficient as a basic supply. This amount corresponds to approximately two portions of oily fish per week.

EPA dosage according to EFSA

  • 250 mg EPA+DHA/day: Normal cardiac, brain and visual function
  • 2,000 mg EPA+DHA/day: Normal triglyceride levels
  • 3,000 mg EPA+DHA/day: Normal blood pressure
  • Maximum 5,000 mg/day rated as safe by EFSA

Between the minimum recommendation and therapeutic dosages there is a large range. In clinical studies on triglyceride reduction or support of mental health, amounts between 1,000 and 4,000 mg of EPA daily were often used. These higher dosages should, however, be agreed with a doctor, as from approximately 3,000 mg of EPA+DHA daily a mild blood-thinning effect can occur, which is relevant for planned operations or when taking anticoagulants simultaneously.

For an individual assessment of your daily omega-3 needs, we recommend our Omega-3 requirements calculator, which takes into account various factors such as body weight, eating habits and health goals.

EPA or DHA — which is more important?

This question is frequently asked but cannot be simply answered — because it is based on a false premise. EPA and DHA are not competitors but complements. They fulfil different main functions in the body and are most effective in this combination.

EPA acts primarily metabolically and as a signal transmitter: it is the precursor of the inflammation-regulating eicosanoids and resolvins, it influences triglyceride levels and platelet activity, and appears to play a special role in mood regulation. DHA, on the other hand, primarily assumes structural functions: it is an essential building block in cell membranes of the brain, retina and sperm cells, and its concentration in neuronal membranes influences their fluidity and thus the transmission efficiency of nerve signals.

Interestingly, the body can convert EPA into DHA to a limited extent (via elongase and delta-6-desaturase), but not DHA back into EPA. This means: those who exclusively take high amounts of DHA could theoretically develop EPA deficits. Conversely, EPA can contribute to DHA supply, albeit inefficiently. Research therefore advocates for products that deliver both fatty acids in a sensible ratio. More details on the structural roles of DHA in the article DHA (Docosahexaenoic Acid).

EPA in specific population groups

Different population groups have an increased or specifically targeted EPA requirement. Athletes benefit from EPA's inflammation-regulating effect in the context of intensive physical exertion: EPA can help modulate the inflammatory response after muscle training and thus possibly support recovery. Studies also show that omega-3 fatty acids can promote muscle protein synthesis in combination with sufficient protein intake.

Older people often have lower omega-3 levels, which correlates with higher inflammatory activity and an increased risk of heart disease. For this group, adequate EPA supply is particularly relevant as the endogenous conversion efficiency from ALA to EPA decreases further with age. Pregnant women should pay special attention to DHA requirements, but EPA is also important for the regulation of inflammatory processes in the placenta. For them, specific recommendations exist that should be medically supervised. Vegans are dependent on algae oil — plant-based ALA sources alone are not sufficient to cover EPA requirements.

Frequently asked questions about EPA (eicosapentaenoic acid)

What is EPA (eicosapentaenoic acid)?

EPA (eicosapentaenoic acid) is a long-chain, polyunsaturated omega-3 fatty acid with 20 carbon atoms and 5 double bonds (C20:5n-3). It is found mainly in oily sea fish and is a direct precursor of inflammation-regulating eicosanoids. The human body can only synthesise it in small amounts from the plant-based alpha-linolenic acid (ALA).

What is EPA good for?

EPA supports normal cardiac function (EFSA-approved health claim at 250 mg EPA+DHA/day), acts as an inflammation regulator through the formation of series-3 prostaglandins and resolvins, and is associated in studies with supporting mental health. At 2,000 mg of EPA+DHA daily, EPA also contributes to the maintenance of normal triglyceride levels.

How much EPA do I need per day?

EFSA recommends 250 mg of EPA+DHA daily for normal cardiac function — achievable through two fish meals per week. For elevated blood lipid levels, 2,000 mg of EPA+DHA may be beneficial; for high blood pressure, up to 3,000 mg. Higher dosages should be medically supervised. EFSA generally rates amounts up to 5,000 mg daily as safe.

What is the difference between EPA and DHA?

Both are marine omega-3 fatty acids but with different main roles: EPA (C20:5) acts primarily as a precursor to inflammation-regulating signalling molecules and is cardioprotectively active. DHA (C22:6) is mainly a structural building block in the brain, retina and sperm cells. The body can convert EPA into DHA to a limited extent, but not vice versa. Both are needed together for an optimal health effect.

Which foods contain a lot of EPA?

The richest EPA sources are oily sea fish: herring (1,000–2,000 mg EPA/100 g), sardines (800–1,500 mg), mackerel (600–1,500 mg), salmon (500–1,200 mg) and tuna (200–700 mg). Plant foods such as linseed oil or walnuts contain no EPA directly — only ALA, which the body can convert very inefficiently. Vegan EPA alternatives are algae oil supplements from EPA-producing microalgae.

Medical disclaimer

This article is for general information only and does not replace medical advice. All health claims are based on EFSA-approved health claims and published studies. If you have specific health questions or are considering taking high doses of omega-3 fatty acids, please consult a doctor or qualified nutritionist.

Further sources

The scientific basis for the statements in this article is based on recognised authorities and published research: