What Is EPA (Eicosapentaenoic Acid)?

EPA, eicosapentaenoic acid, is a long-chain omega-3 fatty acid that your body needs but cannot efficiently produce on its own. Pick up any omega-3 supplement in a health shop and you will find EPA listed somewhere on the back, often buried under a headline "omega-3" figure that tells you remarkably little.

It is one of only two omega-3 fatty acids with an EFSA-authorised health claim for normal heart function, the other being DHA.

Most supplement labels list EPA alongside DHA as though the two are interchangeable. They are not. They concentrate in different tissues, serve different biological roles, and come from different algae species in the supplement world. Knowing which one your product actually delivers matters more than most labels suggest.

EPA Explained: Definition, Structure, and Classification

Eicosapentaenoic acid belongs to the omega-3 family of polyunsaturated fatty acids. Its shorthand, C20:5 n-3, tells you its structure: a 20-carbon chain with five double bonds, the first positioned at the third carbon from the methyl end. That "n-3" designation is what makes it an omega-3 rather than an omega-6, and it determines which metabolic pathways the molecule enters once inside your body.

Within the omega-3 family, EPA sits in the long-chain sub-class alongside DHA (docosahexaenoic acid, C22:6 n-3). Both are distinct from ALA (alpha-linolenic acid, C18:3 n-3), the shorter-chain omega-3 found in flaxseed, chia, and walnuts. ALA is the plant-derived precursor. EPA and DHA are the physiologically active forms your cells use directly.

The classification matters because supplement labels frequently say "omega-3" without specifying which type. When we review the omega-3 products on a typical health shop shelf, the majority lead with the category term and bury the specific fatty acid breakdown in small print on the back.

A product delivering only ALA is not equivalent to one delivering EPA. The molecule is different, the metabolic fate is different, and the evidence base for health effects is different. "Omega-3" alone tells you far less than you might assume.

Where EPA Comes From in Nature and in Supplements

EPA in Oily Fish

Oily fish remain the most concentrated dietary source of preformed EPA for omnivores. A 100g serving of wild salmon provides roughly 500-1,000 mg of combined EPA and DHA, depending on species, season, and whether the fish is farmed or wild. Mackerel, sardines, herring, and anchovies all deliver meaningful amounts.

The NHS recommends two portions of fish per week, one of which should be oily. If you follow that guidance consistently, your EPA intake is likely adequate without supplementation.

But we find that when we ask people directly, the honest answer is often a tin of tuna once a fortnight and nothing else. Tuna is not an oily fish. The gap opens quietly, and most people do not realise it is there.

EPA from Microalgae Sources

Fish are not the origin of EPA. They are the middlemen. The original producers are microalgae, the photosynthetic organisms at the base of the marine food chain. EPA accumulates through the food web: microalgae produce it, small fish eat the algae, larger fish eat the smaller fish, and the omega-3 concentrates at each stage.

Going directly to the source eliminates the intermediary. Nannochloropsis gaditana is the microalgae species with the highest proportion of EPA relative to total fatty acids, which is why it is the primary species used in algae-based EPA supplements.

Not all algae are EPA-rich. When we compared the fatty acid profiles of commercially available algae supplements during our own formulation work, the differences were striking: Schizochytrium, the species behind most "algae oil" products, produces DHA rather than EPA.

Open a Nannochloropsis-based capsule and the oil inside is a deep amber-green with a faintly marine smell. Open a Schizochytrium oil capsule and you get a pale, almost odourless liquid. The visual difference hints at the chemical one. The species on the label determines which fatty acid you are actually getting.

EPA from ALA Conversion in the Body

Your body can convert ALA into EPA through a series of enzymatic steps involving elongation and desaturation. The conversion rate, however, is poor. Published estimates range from 5 to 10%, varying with genetics, sex, age, and the balance of omega-6 in your diet (Burdge and Calder, 2005).

Women of reproductive age appear to convert slightly more efficiently, likely due to oestrogen's influence on delta-6 desaturase activity, but even then the yield is modest.

If you stir a tablespoon of ground flaxseed into your morning porridge, roughly 2,300 mg of ALA, your body might produce 115-230 mg of EPA from it. That is a meaningful contribution, but it is not reliable enough to serve as your sole EPA source if consistent intake matters to you.

We think this is one of the most useful calculations in practical nutrition: do the conversion arithmetic before you assume that flaxseed covers your omega-3 needs.

The Role of EPA in Human Health

The EFSA-Authorised Heart Health Claim for EPA

EPA and DHA contribute to the normal function of the heart. This is an EFSA-authorised health claim under Commission Regulation (EU) No 432/2012, and it applies at a combined daily intake of 250 mg of EPA and DHA. That is the scope of what can be stated with regulatory backing in the UK and EU.

The intake condition is important, and we see it routinely ignored in marketing. A supplement providing 50 mg of EPA per serving does not meet the threshold for this claim on its own.

Next time you pick up an omega-3 bottle in Boots or Holland & Barrett, flip it over and check the actual milligrams per dose against the 250 mg combined figure. If the numbers do not add up, the heart health language on the front is aspirational rather than evidence-based at that dosage.

EPA and Eicosanoid Signalling Pathways

Beyond the authorised heart claim, EPA serves as a precursor to a family of signalling molecules called eicosanoids, including prostaglandins and thromboxanes. These molecules play established roles in the body's inflammatory and immune response pathways. This is standard biochemistry, documented in undergraduate-level nutrition science.

What you will frequently encounter in supplement marketing is the leap from "precursor to anti-inflammatory signalling molecules" to "reduces inflammation." We see this claim on competitor packaging constantly, and it frustrates us because it erodes trust in the category. The mechanism is real. The promised outcome, as a marketable benefit, has not survived regulatory scrutiny.

In our assessment, the honest position is to describe what EPA does biochemically without attaching therapeutic claims the evidence does not yet support at supplement-level doses.

EPA and DHA: Two Omega-3s with Different Jobs

Where EPA and DHA Concentrate in the Body

DHA is the dominant omega-3 in brain and retinal tissue. DHA contributes to the maintenance of normal brain function and normal vision, each at a daily intake of 250 mg (EFSA-authorised claims). EPA, by contrast, circulates more widely and is more heavily involved in eicosanoid metabolism. It does not accumulate in neural tissue the way DHA does.

This distinction matters when you are choosing a supplement. A product labelled "omega-3" that provides only DHA covers the brain and vision claims but does not deliver EPA. A product that provides only EPA covers the heart claim (in combination with DHA from other sources) but does not deliver neural DHA. They are complementary nutrients, not substitutes for each other.

Who Needs to Think About EPA Intake

EPA for Vegans and Vegetarians

If you eat no fish and take no algae-based supplement, your preformed EPA intake is effectively zero. You are relying entirely on ALA conversion, which, as noted above, yields roughly 5-10% efficiency. Seaweed contains trace amounts of EPA, but not enough to meet daily requirements through food alone.

This is not a scare tactic. It is a nutritional gap that we encounter regularly among plant-based eaters, and it persists because the category term "omega-3" appears on flaxseed and walnut packaging at the till, creating the impression that the need is covered.

ALA is an omega-3, but it is not EPA. Your GP is unlikely to test for it unless you ask specifically.

For vegans and vegetarians who want preformed EPA, an algae-derived supplement from Nannochloropsis is currently the only practical route. Our guide to plant-based omega-3 sources covers the options in detail.

EPA for People Who Avoid Oily Fish

You do not need to be vegan to have low EPA intake. If you dislike fish, have concerns about mercury, or simply do not eat oily fish twice a week, the same gap exists.

Fish oil supplements are one option. Algae-based EPA supplements are another. The route depends on your dietary preferences, your budget, and how you feel about the ecological cost of each source.

Two portions of oily fish per week is the NHS benchmark. If you are consistently below that, we would say supplementation is worth considering, whether from fish oil or from algae.

The key is checking that the supplement actually delivers EPA in quantified milligrams, not just omega-3 as a category. We have tested products where the EPA content per capsule was less than a third of what the front label implied.

Choosing an EPA Supplement: What the Label Should Tell You

Three things are worth checking before you buy an EPA supplement, whether you are standing in Holland & Barrett comparing two bottles or scrolling through product listings at home.

EPA content in milligrams per serving. This is the single most important number. A product that says "omega-3 rich" without declaring the actual EPA figure per dose is using adjectives where it should be using data. Your body responds to milligrams, not marketing language. If the EPA content is not stated, you cannot evaluate the product.

Source and species. Fish oil, krill oil, and algae oil all provide different EPA and DHA ratios. Among algae sources, Nannochloropsis is EPA-dominant while Schizochytrium is DHA-dominant. A product labelled "algae omega-3" without naming the species could be delivering primarily DHA. The species determines the fatty acid profile.

Cultivation or sourcing method. For algae-based supplements, whether the microalgae were grown in open ponds or closed photobioreactors affects purity and consistency. For fish oil, the source species and processing method (molecular distillation, for example) affect both the omega-3 concentration and the contaminant profile. Products that are transparent about their supply chain are generally more trustworthy than those that are vague about it.

What Sourcing Plant-Based EPA Taught Us

When we set out to formulate an EPA supplement without fish oil, we expected the hard part to be growing the algae. It was not. The hard part was everything around it: finding the right species, holding it to a consistent standard, and navigating a market where labels obscure more than they reveal.

Most "algae oil" on the market delivers DHA, not EPA. Schizochytrium dominates algae-based omega-3 production because it grows quickly and yields high DHA concentrations. Pick up a vegan omega-3 supplement at random and the odds are strong it contains DHA with little or no EPA. The species on the label determines what you actually get.

EPA concentration in Nannochloropsis varies with cultivation conditions. Temperature, light cycles, and nutrient availability all shift the fatty acid profile from one batch to the next. Open-pond systems are particularly unpredictable. We moved to closed photobioreactors specifically to narrow that variability, because a supplement label promising a set EPA figure has to deliver it consistently.

ALA conversion is too unreliable for most people to depend on. We reviewed years of customer intake patterns and the same story repeated: people eating generous amounts of flaxseed and walnuts assumed their omega-3 needs were covered. The conversion arithmetic says otherwise. At 5-10% efficiency, you would need implausible quantities of ALA-rich foods daily to match a single EPA capsule.

Label transparency on EPA milligrams per serving is surprisingly rare. Walk into any health shop and compare five omega-3 products. Most lead with a total omega-3 figure on the front, and you have to hunt for the EPA breakdown on the back. Some never disclose it at all. If you cannot find the EPA figure per serving, the product is not giving you enough information to decide.

Inflammation claims on competitor packaging routinely lack EFSA authorisation. We see "reduces inflammation" on omega-3 products constantly. The eicosanoid pathway science is real, but the leap to a consumer-facing claim has not been approved by EFSA at supplement doses. It frustrates us because it sets expectations the evidence does not support and erodes trust across the category.

Frequently Asked Questions About EPA

Can you get enough EPA from flaxseed or chia seeds alone?

Unlikely, for most people. Flaxseed and chia provide ALA, which converts to EPA at roughly 5-10%. Even a generous daily intake of ground flaxseed (two tablespoons, providing approximately 4,600 mg of ALA) might yield 230-460 mg of EPA.

That is a useful contribution, but conversion is variable and unreliable as a sole source. A direct EPA source, whether from fish or algae, provides a more predictable intake.

Is EPA or DHA more important?

Neither fully substitutes for the other. DHA concentrates in brain and retinal tissue and carries its own EFSA-authorised claims for brain function and vision. EPA circulates more broadly and serves as the primary precursor for eicosanoid signalling.

Most nutrition guidance recommends a combined intake of 250 mg of EPA and DHA for heart function. If you are choosing between the two, the better question is which one your current diet is actually missing.

Can vegans get EPA without supplements?

Not in meaningful quantities from whole foods alone. Seaweed contains trace EPA, but not enough to meet daily requirements. ALA-rich foods provide a precursor, not the finished molecule.

For reliable preformed EPA on a vegan diet, an algae-based supplement from Nannochloropsis is the practical option. Our overview of marine phytoplankton explains why species choice matters.

How much EPA should you take per day?

The EFSA-authorised health claim for heart function applies at 250 mg of combined EPA and DHA daily. There is no separate regulatory recommendation for EPA alone.

Check the EPA figure on your supplement's nutritional information panel, not the total omega-3 number, and calculate whether you are meeting the threshold from that product alone or in combination with dietary sources.

Does EPA have side effects?

At standard supplement doses, EPA is well-tolerated by most people. At high intakes, generally above 2-3 g of combined EPA and DHA daily, mild anticoagulant effects have been reported. If you are taking blood-thinning medication such as warfarin, speak to your GP before starting a high-dose omega-3 supplement.

Fish oil capsules sometimes cause fishy reflux, that unmistakable repeat an hour after swallowing, which is among the most common reasons people abandon omega-3 supplements altogether. We hear this complaint regularly. Algae-based EPA supplements tend to be better tolerated in this regard, though individual experience varies.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your GP before starting any supplement.

Methodology and Disclosure

Phytality manufactures marine phytoplankton supplements from Nannochloropsis gaditana, which is an EPA-rich microalgae species. We have a direct commercial interest in EPA as a nutrient. This article is editorially independent: the biochemistry, regulatory claims, and conversion-rate data are drawn from published peer-reviewed sources cited above.

The EFSA-authorised health claim for EPA and DHA is cited under Commission Regulation (EU) No 432/2012 with its intake condition (250 mg combined daily) stated. ALA-to-EPA conversion rates are drawn from Burdge and Calder (2005) and Brenna et al. (2009). Species-level distinctions between Nannochloropsis and Schizochytrium reflect established compositional differences documented in Zanella and Vianello (2020).

Where we describe our own formulation decisions (choosing Nannochloropsis, separating EPA and DHA products, using closed photobioreactors), this reflects our actual production process. Eicosanoid pathway descriptions reflect established biochemistry (Calder, 2017). We have explicitly noted where marketing claims exceed the regulatory evidence base.

Last reviewed: March 2026. Next review due: March 2027.