Omega-3
EPA · DHA

Omega-3 is a type of fat. One of the good ones — the kind the body needs and cannot make on its own. But several different fats share that name, and they should not be lumped together. The two that really matter for health are EPA and DHA, which come from the sea — oily fish, shellfish, algae. There is a third, ALA, of plant origin (flax, chia, walnuts), but the body converts it into EPA and DHA with enormous difficulty: only a small fraction ever gets converted. That is why, when we talk about omega-3 with an effect, we are talking mostly about EPA and DHA.

The “3” in the name has a simple chemical explanation: it marks the point in the carbon chain where the first double bond appears. EPA and DHA are the long-chain omega-3s, the ones the body uses directly; ALA is the plant version, shorter, which first has to be elongated and transformed to be of use.

That transformation is the bottleneck. Estimates vary widely from one study to another, but the pattern repeats: the body converts roughly 5–8% of the ALA it takes in into EPA, and considerably less into DHA — from a scant 4% down to figures that some authors consider practically nil in adult men on a Western diet. In young women the conversion is somewhat higher, probably due to hormonal influence (reviews by Burdge and Calder, 2005, and Brenna et al., 2009). The practical consequence you already know: flax and chia add up, but they are not enough as the sole source.

You may have heard of the balance between omega-6 and omega-3. The widespread idea is that the modern diet has too much omega-6 — from seed oils — relative to the 3, and that this would favor inflammation. There is an open scientific debate about how much that ratio matters: some researchers consider it a good indicator, while others hold that what counts is not the ratio but the absolute level of omega-3. The good news is that both camps agree on the practical point: the imbalance is fixed by raising omega-3, not by obsessing over cutting the 6. We return to seed oils in the myths section.

The conversion of ALA into EPA and DHA depends on a chain of enzymes — the Δ6 and Δ5 desaturases and the elongases — that omega-3 shares with omega-6. That is the biochemical basis of the “balance”: linoleic acid (the main omega-6) competes for those same desaturases, so a diet heavily loaded with omega-6 can hinder the already inefficient conversion of ALA. That is the mechanistic argument of those who advocate watching the ratio. The counter-argument, equally legitimate, is that the bottleneck is so narrow that the plant route will never be a serious source of EPA and DHA, whatever the ratio: the real lever is the direct supply from fish or algae.

Omega-3 carries an enormous reputation. The reality, with the data available today, is that it works well for a few things, so-so for others, and for several of its attributed benefits there is no evidence to support them.

In inflammation and joints there is a consistent signal: in rheumatoid arthritis, omega-3 helps reduce the need for anti-inflammatories. In mood, as support for a treatment — not on its own — and with EPA-rich formulas, the effect captured by the studies exists, though it is modest. And in pregnancy, providing DHA is a well-established recommendation of the food safety agencies (around 200 mg a day), with benefit above all in women who start from low levels.

In sport, what is best supported is a modest aid in recovery and muscle soreness after intense efforts. What does not appear in the studies is that it increases muscle mass or performance. The headline “omega-3 to perform better” does not hold up.

In memory and prevention of cognitive decline, the evidence is weak or nil: in already-established dementia it has shown no benefit. Of everything attributed to it, this is the least supported.

The honest story has two parts that should not be mixed. The first: as cardiovascular prevention at the doses of an ordinary supplement (around 1 g a day), the large modern trials have come out neutral. The largest of all, VITAL (Manson, 2019), with nearly 26,000 healthy people, did not reduce the overall set of cardiovascular events; it did point to a reduction in heart attacks as a secondary outcome, more marked among those who ate little fish. ASCEND, in people with diabetes, confirmed that neutrality. The idea of taking a capsule a day “for the heart” has, as of today, no solid support in the general population.

The second part is triglycerides, and here the effect is real and consistent: at high doses (of the order of 2 to 4 g a day) omega-3 lowers them by around 20–30%, according to the American Heart Association itself. This is already therapeutic territory, not maintenance, and it is prescribed with medical judgement.

REDUCE-IT (Bhatt, 2019) did show fewer cardiovascular events. But it comes with three important asterisks. It was done with a prescription drug, not a supplement, based on pure EPA at 4 g a day. Its placebo group used mineral oil, which may have artificially worsened the comparison group, a point still under debate. And a later trial of similar design, STRENGTH, with a different placebo, came out neutral.

In inflammation and joints, the most solid ground is rheumatoid arthritis. Several double-blind trials (Galarraga, 2008; Berbert, 2005) showed what is called an “anti-inflammatory-sparing” effect: patients could reduce their NSAID dose without symptoms worsening. It does not cure the disease, but it improves the management of pain and stiffness. The signal calls for high doses: Galarraga’s own trial used 2.2 g of omega-3 daily.

In depression, omega-3 does not work as an antidepressant on its own, but as support for medication, and with EPA-rich formulas (not DHA), it shows a modest but repeated effect; the fine detail — that formulas with at least 60% EPA are the most effective — comes from reviews such as Liao’s (2019). In prevention, that is, giving omega-3 to people without depression to prevent it, the largest trial (VITAL-DEP, 2021) not only did not help but pointed to a slightly unfavorable signal. As support, yes; as a preventive shield, no.

In pregnancy, DHA is important for the baby’s development, and the recommendation of about 200 mg a day is well established. On something more ambitious — preventing premature birth — the evidence is nuanced: the benefit is concentrated in women who start from low levels of omega-3 (sub-analysis of the ORIP trial). In those who already have a good level, raising the dose adds nothing, and some analysis has even pointed to a possible excess of very late births. More is, once again, not automatically better.

The body of evidence in sport is young and uneven. The most consistent points to recovery: at doses of 2–3 g a day, omega-3 can attenuate muscle soreness and damage markers after an intense effort, although in quite a few trials the improvement falls below what is considered clinically relevant. Where the official position is clear-cut is on the other point: the ISSN position stand (2025) concludes that there is no clear evidence that omega-3 increases muscle mass or performance.

In cognition, the good trials are persistently negative: neither in healthy adults nor in already-established Alzheimer’s has omega-3 moved the needle (VITAL-Cog, 2022; Quinn, 2010). The only chink of light appears in some subgroup with mild cognitive impairment, not in established dementia. European regulation only allows the claim “maintenance of normal brain function” with 250 mg of DHA a day — a maintenance message, not one of improvement.

Why does a fish fat do anything in the body? EPA and DHA are incorporated into the membranes of our cells, and from there they act on three fronts.

First, they partly displace arachidonic acid (an omega-6) from the membrane. When the cell makes its inflammatory messengers — the eicosanoids — starting from EPA instead of arachidonic acid produces less inflammatory versions. It is a change of raw material that lowers the baseline inflammatory tone.

Second, and more interesting: omega-3 not only switches off inflammation, it helps to resolve it actively. From it derive molecules called specialized pro-resolving mediators — resolvins, protectins, maresins — that orchestrate the end of the inflammatory response and the clean-up of the tissue. Putting out a fire and clearing the rubble are different things; omega-3 takes part in both.

Third, it acts as a signal. Through a cellular receptor (GPR120/FFAR4) it modulates pathways such as that of the NF-κB factor, central to inflammation, and in the liver it reprograms fat metabolism by reducing the production of triglycerides — the mechanism that explains its most solid effect.

Two near-twin trials — both at 4 g/day, in high-risk patients with high triglycerides and a statin — gave opposite results: REDUCE-IT (pure EPA) reduced events by 25%; STRENGTH (EPA+DHA) was neutral and was stopped for futility. There are two rival explanations. The “EPA hypothesis” holds that isolated EPA has properties that the mixture with DHA dilutes. The “placebo hypothesis” holds that the mineral oil used as control in REDUCE-IT may have worsened the markers of the placebo group and artificially inflated the contrast; STRENGTH used corn oil, more neutral. As of today the debate is not settled, and that is why neither reading should be presented as a closed fact.

It makes more sense to consider omega-3 if you eat little oily fish, if you have high triglycerides, during pregnancy (for the DHA), or if you live with an inflammatory disease such as rheumatoid arthritis. For someone who already eats oily fish two or three times a week, the first “source” should be the plate, not the bottle.

Doses change depending on what for. For general maintenance, what a couple of servings of oily fish a week provide is usually enough. To lower triglycerides, considerably higher doses are needed, and that is already the territory of medical supervision. Take it with a meal that has some fat in it, because it improves its absorption quite a bit.

When you read the label, look at the milligrams of EPA and DHA, not those of “fish oil” in total. A “1,000 mg” bottle may have only 300 mg of what really matters.

And, contrary to what instinct suggests, more is not better: at very high doses risks appear, as we will see at the end.

As an orienting reference:

The safety ceiling set by EFSA is 5 g a day of EPA+DHA; the U.S. agency (FDA) is more conservative and places the consumption “recognized as safe” at 3 g a day. Going beyond that adds nothing and, as we will see, beyond a certain point it adds risks.

Omega-3 does not act from one day to the next. When you start taking it, your Index rises little by little and takes about 3 or 4 months to stabilize at its new level. It is a long-haul supplement, not one of immediate effect.

The effect of taking it with fat is large: a meal with enough fat can multiply by up to four the absorption of some forms — specifically the ethyl esters, the most sensitive to this. Taking the capsule on an empty stomach or with a very light meal is wasting it.

The difference between forms is not just theoretical: at equal doses, re-esterified triglyceride achieves better incorporation into the Omega-3 Index than ethyl ester over the medium term (Neubronner, 2011), although the gap narrows if the ethyl ester is always taken with a fatty meal. For most people, however, adherence and product quality weigh more than the specific chemical form.

Not entirely. Fish oil is the classic form. Algae oil is the option for vegans or for those allergic to fish, and it provides the same EPA and DHA: it is not a second-rate version. Krill tends to sit better with those who get fishy reflux. And plant ALA (flax, chia) does provide omega-3, yes, but the body makes poor use of it to produce EPA and DHA, so it does not replace the previous ones.

Behind the forms there is chemistry, and the chemistry changes how much omega-3 ends up reaching your blood. The natural form in fish is the triglyceride (TG), which is taken as the reference. Concentrates usually come as re-esterified triglyceride (rTG) or as ethyl ester (EE): rTG is absorbed somewhat better, and EE — the form of the drugs — performs worse on an empty stomach but evens out if you take it with a fatty meal. Krill carries omega-3 bound to phospholipids and to a natural antioxidant, astaxanthin; it has been suggested that it is absorbed better per milligram, although that point remains under debate, because the studies do not always compare equivalent doses. And algae oil is, with no asterisks, equivalent to fish oil: the fully legitimate vegan option.

The supposed superiority of krill carries a methodological problem: several studies that support it were comparing non-equivalent omega-3 doses, which biases the result in its favor. When doses are matched, the advantage fades. It is a good example of why it is worth reading the fine print of each comparison.

Omega-3 is a delicate product: it oxidizes (goes rancid) easily, and coming from the sea it can carry contaminants. That is why it is worth looking at independent quality seals. In Europe the most relevant is IFOS, which analyzes the product batch by batch.

IFOS: it publishes a batch-by-batch analysis, with a certificate you can check for the specific bottle in your hand, and it measures potency, oxidation, heavy metals, PCBs and dioxins. It has sister programs for krill (IKOS) and for algae (IAOS).

GOED works as the sector’s measuring stick: it sets the oxidation limits the industry accepts as tolerable. And for athletes there is a separate group — NSF Certified for Sport and Informed Sport — which, besides quality, guarantee the absence of doping substances; they are the ones the federations require.

Rancid oil not only tastes worse: it loses part of its value. That is why opaque packaging, an airtight seal and the expiry date matter as much as the milligrams on the label.

A selection of the trials that support what is said above. Here they are summarized; at the advanced level each one unfolds with its methodology, its figures and its link.

Safety meta-analysis (Gencer, 2021). It pooled several large trials and confirmed a dose-dependent increase in atrial fibrillation. The main safety signal of omega-3, presented as context, not as an isolated study.

That “seed oils (omega-6) are inflammatory”: it is a debated and probably exaggerated matter; the problem with the modern diet is not so much the excess of 6 as the lack of 3. And that “it helps you lose weight”: its effect on weight is, in practice, irrelevant.

The accusation is that their omega-6 “inflames”. The current evidence does not support it: in large population analyses, the main dietary omega-6 — linoleic acid — is associated rather with lower cardiovascular and diabetes risk, not higher. In fact, the American Heart Association recommends keeping a certain intake of omega-6 and warns that cutting it excessively could be counterproductive. The reasonable consensus today is clear: the problem is not having “too much 6”, but having “too little 3”.

Krill is often sold as superior to fish oil; the evidence is mixed and, adjusting for dose, there is no clear winner. And omega-3 as a remedy for ADHD: an effect exists, but a small one, well below the usual medication; it is not a treatment.

Circulating linoleic acid has been associated, in large pooled analyses of cohorts from the FORCE consortium, with lower cardiovascular risk (Marklund 2019; Circulation 2019;139(21):2422–2436; DOI: 10.1161/CIRCULATIONAHA.118.038908) and with lower type 2 diabetes risk (Wu 2017; Lancet Diabetes Endocrinol 2017;5(12):965–974; DOI: 10.1016/S2213-8587(17)30307-8); and above a certain intake threshold (around 2% of energy) it stops raising tissue arachidonic acid, which deactivates the causal chain the myth presupposes. The American Heart Association, in a 2009 scientific advisory, recommended keeping omega-6 at 5–10% of energy and warned that reducing it could increase coronary risk (AHA Science Advisory; Circulation 2009;119:902–907; DOI: 10.1161/CIRCULATIONAHA.108.191627).

In this debate, part of the evidence favorable to linoleic acid has had funding from the seed-oil industry; the main proponent of the Omega-3 Index (W. S. Harris) founded and retains an equity stake in an omega-3 testing company (OmegaQuant); and the main driver of the ratio thesis (A. P. Simopoulos) runs a center that disseminates information on the subject. No conflict on its own invalidates the data, but they all oblige us to read it with a critical eye.

The optimal dose of omega-3 to prevent cardiovascular problems in healthy people is not known — quite simply, there is no consensus. The trial that would settle the REDUCE-IT debate has not yet been done: comparing the drug against a truly neutral placebo. It is not well understood why high doses favor atrial fibrillation. And in depression it remains unclear who responds and who does not, although the clues point to people with elevated inflammation.

Several open fronts remain: whether the “EPA hypothesis” is real or an artifact of the REDUCE-IT placebo; by what exact mechanism high doses induce atrial fibrillation (effects on the electrical conduction of the membrane are considered, unconfirmed); which subgroup of patients with depression truly responds to EPA; and whether the differences in bioavailability between forms end up translating into different clinical outcomes, something no trial has compared head-on.

Here we must speak with honesty and caution, because each person’s health is at stake.

In pregnancy, DHA is advisable, but one should watch out for cod liver oil: its excess of vitamin A can harm the fetus. Better a standardized fish or algae oil.

At high doses, omega-3 is associated with a higher risk of atrial fibrillation (a heart arrhythmia). It is the main reason why “more” does not mean “better”.

And, as with any supplement, this information does not replace the advice of a healthcare professional.

Several large trials with doses of 1 g or more a day found more cases of this arrhythmia in the omega-3 group than in placebo, and the Gencer (2021) meta-analysis confirmed it with a dose-dependent pattern: the higher the dose, the higher the relative risk. It is not cause for alarm at maintenance doses, but it is a weighty reason not to “load up” on your own.

A minor but real effect: fishy burps and digestive discomfort, more frequent with the ethyl esters. They are reduced by taking the capsule with food and keeping it in the fridge.

On atrial fibrillation, the two large drug trials at 4 g/day confirm it as a class signal: REDUCE-IT (hospitalization for AF/flutter 3.1% vs 2.1%) and STRENGTH (new-onset AF 2.2% vs 1.3%). The mechanism is not clarified. The prudent reading: the absolute risk is small and concentrated in high doses and high cardiovascular-risk patients, not in the maintenance dose.

On bleeding, the Javaid (2024) meta-analysis, with 15 trials and 120,643 patients, found no increase in the overall bleeding risk, not even alongside antiplatelet agents; only pure EPA at a high dose showed a slight increase of minimal clinical impact. The perioperative warning and the one with anticoagulants is kept out of prudence, not because of a strong signal.

Safety citations: Gencer B, et al. Circulation 2021;144:1981-1990 (DOI: 10.1161/CIRCULATIONAHA.121.055654); Javaid M, et al. J Am Heart Assoc 2024;13:e032390 (DOI: 10.1161/JAHA.123.032390).