Omega-3 Fatty Acids and Heart Health: Fish Oil, Prescription EPA, and the Evidence

Medical Disclaimer: This content is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Information is based on current medical literature and clinical guidelines but may not apply to your specific situation. Individual responses vary based on personal medical history and concurrent conditions. Always consult qualified healthcare providers for medical decisions. Never delay seeking medical care based on content you’ve read. If experiencing a medical emergency, seek immediate medical attention.

These articles provide education to enhance your healthcare partnership. All treatment decisions should involve your healthcare team. Use this knowledge to have informed discussions, not to replace medical care.

In brief: Omega-3s are not one intervention but three: dietary fish, over-the-counter fish oil, and prescription-grade purified EPA, each with a different evidence base. Most people who take fish oil to prevent a heart attack are using a dose and formulation that no modern randomized trial has shown to reduce cardiovascular events. One specific product — high-dose purified EPA (icosapent ethyl) at 4 grams a day — did reduce events in a defined high-risk group, but it is a prescription drug, it carries an atrial fibrillation signal, and an unresolved question hangs over its trial design. The fish oil on a pharmacy shelf is not the drug that was tested.

Three Different Things People Call “Omega-3s”

Almost every misunderstanding about omega-3s comes from treating these three as one. They are not interchangeable.

Dietary fatty fish is a food. Eating fish such as salmon, mackerel, sardines, or herring is associated with lower cardiovascular risk across many observational studies. (1) The omega-3s arrive alongside protein, selenium, vitamin D, and other nutrients, and a capsule does not reproduce that package.

Over-the-counter fish oil is a supplement. A typical capsule supplies 300–500 mg of combined EPA and DHA — often only 30–60% of the oil by weight — compared with the 85–96% concentration of pharmaceutical-grade products. (21) Large trials have tested this kind of dose, and they did not find a reduction in cardiovascular events. (10,11,12,19)

Prescription icosapent ethyl (Vascepa) is a drug: 96% pure EPA, taken at 4 grams a day. It holds FDA approval to reduce cardiovascular risk in a specific high-risk group — statin-treated adults with elevated triglycerides who have established cardiovascular disease, or diabetes plus other risk factors. (14,27) That is a higher evidentiary bar than any supplement claim, and it is the only omega-3 product to clear it.

The marketing of fish oil depends on blurring these categories.

Find Your Situation

This table is a tool to help you locate yourself in the evidence and prepare for a conversation with your own clinician — not a set of instructions, and not a substitute for individual medical judgment. Each row is explained in the sections that follow.

How Omega-3s Affect Cardiovascular Biology

Omega-3s do three things that matter to the heart: they lower triglycerides reliably, they influence inflammation, and they change how heart-muscle cells handle electrical signals. Understanding these effects also explains why they do not always translate into fewer heart attacks.

Omega-3 fatty acids are polyunsaturated fats the body cannot build from scratch. The marine forms, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), come from fatty fish and are the forms studied in cardiovascular trials. The plant form, ALA (from flaxseed, walnuts, and chia), converts to EPA and DHA inefficiently — only a small percentage to EPA and well under 1% to DHA in most people, with somewhat higher conversion in women. (2) A flaxseed supplement therefore delivers very little of the omega-3s that matter for the heart.

Triglyceride lowering is the best-established effect. EPA and DHA reduce the liver’s output of VLDL particles, which carry triglycerides through the blood, and help clear triglycerides from circulation. (5) At adequate doses the effect is large and consistent across formulations, and the higher someone’s starting triglycerides, the larger the absolute drop tends to be. But lowering triglycerides is not the same as preventing heart attacks. Article 3 covers why: several drug classes lower triglycerides without reducing cardiovascular events, because the triglyceride number reflects both causal biology and broader metabolic dysfunction. Moving the number does not reliably move the disease.

Inflammation resolution is more distinctive. EPA and DHA compete with arachidonic acid, an omega-6 fat the body uses to make pro-inflammatory signals, and they serve as building blocks for resolvins and protectins — molecules that help the body actively shut inflammation down rather than just suppressing it. (3,4) Most anti-inflammatory drugs act like a fire extinguisher; EPA appears to help the fire burn out cleanly. That distinction may matter in atherosclerosis, where low-grade inflammation inside artery walls drives plaque growth, and EPA has the strongest outcome data of any omega-3 form tested. (4)

Membrane and electrical effects cut both ways. EPA and DHA embed in heart-cell membranes and change how ion channels behave. In the laboratory this can steady cells against dangerous rhythms; in people, high-dose omega-3 use is linked to more atrial fibrillation, covered in the safety section. (6,22) The same property that calms one electrical problem can provoke another.

These are broad metabolic effects, not a targeted drug action — which is part of why the benefit is so dependent on dose, formulation, and who is taking it.

The Observational Foundation, and Its Limits

People who eat more fatty fish have fewer cardiovascular events, and blood levels of EPA and DHA track inversely with risk across many cohorts. (1) The biology is coherent and the associations are real. But association is not proof of benefit from a supplement. People who eat fish regularly differ from those who do not in diet, income, and habits, and the omega-3s in fish arrive with nutrients a capsule lacks. The observational data were strong enough to justify randomized trials — and those trials are where the story gets specific.

The Trial Landscape

At first glance the trials look contradictory. Placed side by side, they are not. Four variables — dose, formulation (pure EPA versus EPA+DHA), the era of background therapy, and the patient’s baseline risk — track the results almost perfectly.

The dose-and-formulation column tells the story. Every trial with a positive cardiovascular signal used pure EPA (JELIS, REDUCE-IT, RESPECT-EPA) or predated modern statin therapy (GISSI). The EPA+DHA trials at consumer-level doses showed no benefit, and the one high-dose EPA+DHA trial (STRENGTH) failed as well. The fish-oil capsule in a medicine cabinet and the drug in REDUCE-IT share a name and a molecular family; pharmacologically, they behave like different drugs.

The sections below walk these trials from biology to outcomes — the Outcomes Ladder from Article 3. Triglycerides fell and inflammatory markers shifted in nearly every trial. Whether those changes prevented heart attacks, strokes, and cardiovascular deaths is a separate question, and the answer depended entirely on which omega-3, at what dose, in whom.

Early Evidence: GISSI-Prevenzione (1999)

GISSI-Prevenzione enrolled 11,324 patients who had recently survived a heart attack and assigned them to about 0.85 g/day of EPA+DHA (a 1-gram capsule), vitamin E, both, or neither, for 3.5 years. (7) In the analysis by treatment group, the omega-3 group had roughly a 15% lower rate of the primary endpoint (death, non-fatal MI, and stroke), with the benefit driven mainly by a reduction in death — about 20% lower all-cause mortality and roughly 30% lower cardiovascular mortality. (7) The more conservative factorial analysis produced smaller estimates, but the mortality signal was the trial’s most robust finding.

The decisive caveat is the calendar. GISSI enrolled patients in 1993–1995, when statins were barely in use — fewer than 5% of participants took one at baseline. (7) Later trials in statin-treated patients did not reproduce the benefit. The lesson is not that GISSI was wrong; it is that background treatment matters. A therapy can look effective when patients are not yet receiving modern statins, antiplatelet drugs, blood-pressure control, and cardiac rehabilitation. Once those reduce baseline risk, adding a supplement on top has far less room to help.

Japanese Evidence: JELIS (2007)

JELIS enrolled 18,645 Japanese patients with high cholesterol and assigned them to purified EPA (1.8 g/day) plus a statin, or a statin alone. Over a mean of 4.6 years, the EPA group had 19% fewer major coronary events (262 events, 2.8%, versus 324, 3.5%; p=0.011), with the largest benefit in patients who had elevated triglycerides. (8) JELIS is notable for testing pure EPA and for using a blinded committee to adjudicate outcomes, which offsets some of the limitation of its open-label design.

Two cautions apply. The absolute difference was 0.7 percentage points — about one event avoided for every 140 patients treated over those years — so a 19% relative reduction translated into a modest absolute one. And the Japanese population began with much higher fish intake and blood EPA levels than Western populations, which limits how far the result transfers. JELIS supports the idea that EPA specifically may help; it does not show that standard Western fish oil reduces events.

More EPA Evidence: RESPECT-EPA (2024)

RESPECT-EPA tested purified EPA (1.8 g/day) added to a statin in 2,506 Japanese patients with stable coronary disease and low baseline EPA levels. The primary composite endpoint was lower with EPA but just missed significance (10.9% versus 14.9%; HR 0.79, 95% CI 0.62–1.00; p=0.055), while a secondary coronary-event endpoint was significantly reduced. (9) The trial was open-label, not placebo-controlled, and underpowered, and the same Japanese-population limits apply. It points in the same direction as JELIS and REDUCE-IT without settling the question on its own.

The Null Era: ORIGIN, ASCEND, and VITAL

Three large, well-conducted trials tested omega-3 at about 1 gram a day and found no reduction in cardiovascular events.

ORIGIN (2012) gave ~1 g/day to 12,536 patients with dysglycemia (pre-diabetes or early type 2 diabetes) and found no difference in cardiovascular death versus an olive-oil placebo. (12)

ASCEND (2018) gave ~1 g/day to 15,480 patients with diabetes and no cardiovascular disease. Serious vascular events occurred in 8.9% of the omega-3 group and 9.2% of the placebo group — no significant difference. (10) Diabetes is a high-risk state, and many patients with diabetes take fish oil hoping to lower future risk; this trial did not support that.

VITAL (2019) gave ~1 g/day to 25,871 generally healthy adults. The primary cardiovascular endpoint was not significantly reduced (HR 0.92, 95% CI 0.80–1.06). A prespecified secondary analysis showed fewer heart attacks (HR 0.72, 95% CI 0.59–0.90), which is worth noting but, as a secondary finding from a trial that missed its primary endpoint, is hypothesis-generating rather than proof. (11)

At doses close to what consumer supplements provide, omega-3s did not reduce cardiovascular events in these modern trials.

The Pivotal and Contested Trial: REDUCE-IT (2019)

REDUCE-IT is the reason prescription EPA exists as a cardiovascular drug. It enrolled 8,179 statin-treated patients with elevated triglycerides (150–499 mg/dL) who either had established cardiovascular disease (71%) or diabetes plus another risk factor (29%), and assigned them to icosapent ethyl — 96% pure EPA — at 4 g/day or to a mineral-oil placebo, with a median follow-up of 4.9 years. (14)

The results were substantial. Major cardiovascular events fell by 25% (17.2% versus 22.0%; HR 0.75, 95% CI 0.68–0.83). Non-fatal heart attacks fell 31%, stroke 28%, and cardiovascular death 20%. The absolute reduction in the primary endpoint was 4.8 percentage points, a number needed to treat of about 21 over roughly five years — meaning that treating 21 such high-risk patients for about five years prevented one major cardiovascular event. (14) That is a clinically meaningful benefit in a high-risk group.

It applies to that group. The patients had established disease or diabetes, elevated triglycerides, and were already on statins, and the drug was high-dose pure EPA under pharmaceutical manufacturing. None of that describes a low-dose, mixed-EPA+DHA capsule bought off a shelf. REDUCE-IT supports prescription EPA in selected high-risk patients; it does not validate consumer fish oil. The benefit was also larger than triglyceride lowering alone would predict, which suggests EPA acts on plaque biology and inflammation, not just the lipid number. On the strength of the trial, the FDA approved icosapent ethyl for cardiovascular risk reduction, and the 2021 ACC Expert Consensus Decision Pathway recommends considering it in statin-treated patients with triglycerides of 135–499 mg/dL who remain at elevated risk. (27)

Why the trial is debated. The placebo was mineral oil, which is not inert when taken daily. In the placebo group, LDL cholesterol rose by about 10% and inflammatory markers increased. (14,27) Critics argue this made the comparator group look worse and exaggerated the apparent benefit; the investigators counter that the placebo-arm changes were too small to explain a 25% reduction, and the FDA approved the drug after reviewing the concern. Most skeptics are not arguing the drug does nothing — they argue the true effect may be smaller than reported, perhaps closer to 15% than 25%. RESPECT-EPA, which used an inert control, pointed the same way without reaching significance (9), consistent with a real but possibly smaller effect. REDUCE-IT remains the best evidence for high-dose purified EPA: a large, important signal with a genuine, unresolved question attached. That conversation belongs with a physician, not at a pharmacy counter.

Imaging Support: EVAPORATE (2020)

EVAPORATE used serial CT angiography in statin-treated patients and found that icosapent ethyl reduced low-attenuation plaque — the soft, lipid-rich, rupture-prone kind — by about 17% over 18 months, while it grew by 109% in the placebo group. (15) It was not an outcomes trial, but it supports the idea that EPA changes plaque biology, not just blood lipids.

The Counterpoint: STRENGTH (2020)

STRENGTH enrolled 13,078 statin-treated, high-risk patients with elevated triglycerides and gave them 4 g/day of an EPA+DHA carboxylic-acid formulation versus a corn-oil placebo. It was stopped early for futility, with a final hazard ratio of 0.99 (95% CI 0.90–1.09). (17) Same dose as REDUCE-IT, similar patients, different molecule — and no benefit. EPA and DHA have overlapping but distinct effects on lipids, membranes, and inflammation, and the combination did not deliver what pure EPA did.

One secondary analysis sharpens the point: blood EPA levels rose far more in REDUCE-IT than in STRENGTH despite similar dosing, and in STRENGTH no relationship appeared between achieved blood levels and outcomes. (16) What reaches the bloodstream may matter as much as the dose on the label. But that higher achieved EPA is only one of several candidate explanations for why the two trials diverged, none of them settled: alongside it sit the mineral-oil placebo that may have worsened REDUCE-IT’s comparator arm, genuine biological differences between EPA and DHA, and somewhat different patient populations. Whatever the explanation, the practical conclusion is firm: omega-3 benefit is not a class effect, current guidelines endorse icosapent ethyl rather than EPA+DHA combinations for cardiovascular risk reduction, and high-dose EPA+DHA has no FDA cardiovascular approval and no supporting outcome trial. (17,27)

What the Evidence Supports, and What It Doesn’t

The table below sorts the main omega-3 claims into what randomized trials actually show, with a plain-language reading of each.

The biology is real and the dietary association is real. The clinical outcome evidence is specific to one product and one population. Major cardiovascular guidelines do not recommend routine over-the-counter fish-oil supplementation for primary prevention. (20) Treating biology and outcomes as the same thing is where most omega-3 decisions go wrong.

Safety and Side Effects

Omega-3s are often assumed to be harmless because they come from fish. They are biologically active, and at higher doses they have real, dose- and formulation-dependent effects.

Atrial fibrillation — the most important signal. Atrial fibrillation is a disorganized heart rhythm that causes palpitations, breathlessness, and fatigue, and raises stroke risk. In REDUCE-IT, hospitalization for atrial fibrillation or flutter occurred in 3.1% of the icosapent ethyl group versus 2.1% on placebo. (14) A 2021 meta-analysis of cardiovascular outcome trials confirmed the association, which grows with dose and is most apparent above about 1 gram a day. (22) The absolute increase in REDUCE-IT was roughly one extra case per 100 patients treated over nearly five years — set against one major cardiovascular event prevented per 21 treated. For someone with prior atrial fibrillation, an enlarged atrium, structural heart disease, sleep apnea, heavy alcohol use, or prior cardioversion, that trade-off carries more weight. This is not a reason to avoid high-dose EPA when it is clearly indicated, but it is a reason the decision belongs with a cardiologist. The benefit and the risk travel together; both have to be weighed.

Bleeding — usually small. A 2024 meta-analysis of 11 trials and 120,643 patients found no overall increase in bleeding with omega-3 — including serious bleeding such as intracranial hemorrhage — and no increase among patients also on antiplatelet therapy. (24) Restricted to high-dose purified EPA, a small signal appeared — an absolute increase of about 0.6%. Standard-dose supplementation does not appear to raise bleeding risk meaningfully, but any omega-3 use should be disclosed to clinicians managing anticoagulation, especially before procedures.

Gastrointestinal effects — the usual reason people quit. A meta-analysis of 90 trials found omega-3 significantly increased the odds of diarrhea (OR 1.26) and altered taste, including fishy aftertaste (OR 3.48). (23) Taking the product with meals reduces these symptoms; enteric-coated forms cut the fishy aftertaste; and rancid, oxidized oil makes both worse — another reason quality matters.

LDL cholesterol — formulation-specific. At high doses, EPA+DHA combinations can modestly raise LDL cholesterol, an effect driven by DHA. Pure EPA does not raise LDL and may lower it slightly. (17) This matters because most people taking omega-3 for their heart are also working to lower LDL, and it may help explain why pure-EPA REDUCE-IT succeeded where EPA+DHA STRENGTH did not. The LDL rise with DHA does not consistently increase ApoB, the count of atherogenic particles, so without an ApoB measurement the significance of these LDL changes is uncertain.

Fish and shellfish allergy. The FDA label for icosapent ethyl notes that the risk in patients with fish or shellfish allergy is unknown, and reactions to fish oil have been reported in people with seafood allergy. Discuss this with a physician before any marine omega-3 product.

Product quality and oxidation. OTC fish oil is not held to pharmaceutical standards, and independent testing has found label inaccuracies and oxidation in commercial products. (21) Oxidized fish oil is not neutral: as the fats break down they form reactive byproducts that can promote oxidative stress rather than the resolution that intact omega-3s support. Oxidation is simply the oil turning rancid, and it builds up over time and speeds up with heat, light, and air — so an older bottle, or one stored warm, in sunlight, or left open, is more likely to have degraded, and a strong fishy or sour smell is often the tell. The supplement many people take may not match what trials studied in potency or freshness. The IFOS (International Fish Oil Standards) program publishes independent purity, potency, and freshness testing at ifos.com. As Article 2 covers, certification verifies what is in the bottle, not whether what is in the bottle has outcome evidence — but for fish oil, where oxidation is a documented problem, it is a reasonable baseline.

Prostate cancer — an unsettled signal. A 2013 analysis within the SELECT trial cohort linked higher blood omega-3 levels to prostate cancer risk. (25) The finding drew attention but remains contested: it was observational within the cohort, omega-3 was not given as a randomized fish-oil intervention, and later evidence has not established cause. It is not strong enough to drive most decisions, but it is worth noting for patients with specific concerns.

The message is not that omega-3s are dangerous. It is that they are active compounds with trade-offs that depend on dose, formulation, and the person. In a high-risk patient taking prescription EPA for a proven indication, those trade-offs can be worth accepting. In a low-risk person taking OTC fish oil with no outcome evidence behind it, the same trade-offs are harder to justify.

Diet First, for Almost Everyone

Two servings of fatty fish a week provide roughly 500 mg of EPA+DHA a day — close to the supplement doses that showed no benefit in modern trials. (1,20) That does not make dietary fish pointless: food and capsules are different exposures, and the dietary association with lower risk is consistent and comes packaged with protein, selenium, and vitamin D. Eating fish regularly often signals a healthier overall diet, so some of the benefit seen in population studies likely reflects the whole eating pattern rather than the omega-3 alone — another reason a capsule cannot stand in for the food. Preparation matters — baked, grilled, or broiled fish tracks with lower cardiovascular risk, while fried fish does not, so the best sources are salmon, mackerel, sardines, anchovies, and herring, not a fried fillet. (1,26)

Diet cannot reach 4 grams of pure EPA a day. For the specific high-risk patient where that dose is indicated, prescription treatment is the only way to get there. For everyone else, the evidence favors dietary fish over an OTC capsule.

If You Already Take Fish Oil

Many readers already take OTC fish oil, often on a doctor’s word or a label claim. That was not irrational, and there is no evidence it caused harm. The evidence simply is this: standard-dose OTC fish oil has not been shown to reduce cardiovascular events in modern trials. (10,11,12,19) If you have been taking it for general heart protection and your risk is low to moderate, that evidence is worth knowing — but whether to continue is a decision for you and your clinician, not a step to take on your own after reading this. If a clinician recommended it for a specific reason, that recommendation may reflect factors this article cannot see, and is worth discussing directly with them. The more useful question for most people is whether their risk profile, triglycerides, and history place them in the group where prescription EPA has demonstrated benefit — again, a conversation for the clinic.

Two Patients, One Supplement Aisle

Both are composites built from the populations the trials actually studied.

Patient A is a 67-year-old man with a prior heart attack, type 2 diabetes, an LDL of 70 on a moderate-intensity statin, triglycerides of 220 mg/dL, and no history of atrial fibrillation. He asks whether to add fish oil. He matches the REDUCE-IT profile almost exactly. (14) For an illustrative case like his, the evidence would support discussing prescription icosapent ethyl with his clinician — not reaching for OTC fish oil — weighing an expected benefit of roughly one major cardiovascular event prevented per 21 patients treated for about five years against roughly one extra atrial fibrillation hospitalization per 100 treated. (14,22) The actual decision would rest with him and his physician, accounting for details a composite cannot capture.

Patient B is a 52-year-old woman with no cardiovascular disease, normal triglycerides and LDL, and no diabetes, who has taken 1,000 mg of fish oil daily for five years because a neighbor recommended it. She matches no trial population in which omega-3 reduced events; her dose sits in the range tested by ORIGIN, ASCEND, VITAL, and OMEMI, where it did not help. (10,11,12,13) Her risk is already low, and the trial evidence gives little reason to expect the supplement to lower it further. For someone in her situation, the evidence points toward dietary fish two or three times a week rather than a capsule — though, as always, what she does is hers to decide with her clinician. (1,20)

Same supplement, different patients, different answers. That is the entire point.

Navigating the Prescription Pathway

If you fit the REDUCE-IT profile — established cardiovascular disease or diabetes with elevated triglycerides, already on a statin — this is the kind of conversation worth having with your clinician, who can weigh it against your full history. Icosapent ethyl (brand name Vascepa) is the prescription product studied in this population, and whether it is right for you is a clinical judgment, not something to decide from an article. Bringing your most recent triglyceride result to the appointment helps. A thorough discussion usually covers whether your triglycerides and risk profile resemble the patients who benefited in REDUCE-IT, whether you have any history of atrial fibrillation or risk factors for it, the absolute benefit and risk for someone in your situation, and any interactions with your current medications. Insurers often require prior authorization, which a prescriber’s office can handle, and a generic version is now available in the United States, so a pharmacist can advise on current pricing.

Common Misconceptions

“Fish oil supplements are the same as prescription omega-3.” They are not. REDUCE-IT studied 96% pure EPA at 4 g/day under pharmaceutical manufacturing. (14) Consumer fish oil, at the doses people take, has not reduced cardiovascular events. (10,11,12,19)

“Lowering triglycerides automatically lowers heart-attack risk.” It does not. Several therapies lower triglycerides without reducing events — the marker-versus-cause distinction from Article 3. Benefit depends on mechanism and patient, not the number alone.

“1,000 mg of fish oil means 1,000 mg of omega-3.” A 1,000 mg capsule typically contains 300–500 mg of actual EPA+DHA; the rest is other fats from the oil. (21)

“Omega-3s are risk-free because they come from fish.” High-dose omega-3 raises atrial fibrillation risk (14,22), oxidized fish oil can promote oxidative stress (21), and label inaccuracies are documented. (21) Natural origin does not mean no risk.

The Bottom Line

Dietary fish, OTC fish oil, and prescription purified EPA share a name and a molecular family but carry three different evidence bases. At consumer doses, modern randomized trials have not shown a reduction in cardiovascular events. (10,11,12,19) One prescription product — pure EPA at 4 g/day — cut events by 25% in a defined high-risk group (14), but it carries an atrial fibrillation signal (14,22) and applies only to statin-treated patients with established disease or diabetes and elevated triglycerides. It does not apply to the general public buying capsules off a shelf.

Three things are worth carrying away. A 1,000 mg fish-oil capsule holds only 300–500 mg of actual EPA+DHA, well below the dose that showed benefit. (21) EPA and DHA are not equivalent; the outcome evidence belongs to purified EPA, not to EPA+DHA combinations. (14,17) And if you have established heart disease, diabetes, elevated triglycerides, and are already on a statin, the evidence supports a conversation about prescription icosapent ethyl — not an OTC supplement. (14,27) For everyone else, two servings of fatty fish a week is the most defensible approach the evidence supports. (1,20) The question is not whether omega-3s work. It is which omega-3, at what dose, in which patient, and for which outcome.

Article 5 covers CoQ10 — a supplement where the biology is real, one trial showed meaningful benefit in heart failure, and most people who buy it have neither heart failure nor a condition it has been shown to improve.

Key Terms

ALA (alpha-linolenic acid). The plant omega-3 in flaxseed, walnuts, and chia. The body converts it to EPA and DHA inefficiently, so it is a poor substitute for marine omega-3s for cardiovascular purposes.

ApoB (apolipoprotein B). A protein on each LDL particle. Counting ApoB counts atherogenic particles directly, a more precise measure of risk than LDL cholesterol concentration alone.

Atrial fibrillation (AF). A disorganized rhythm of the upper heart chambers that causes palpitations and fatigue and raises stroke risk. High-dose omega-3 modestly increases its risk.

DHA (docosahexaenoic acid). A marine omega-3 often paired with EPA in supplements. At high doses it can modestly raise LDL cholesterol, a likely reason EPA+DHA combinations have not reduced events in trials.

EPA (eicosapentaenoic acid). A marine omega-3 with distinct inflammation-resolution biology and the strongest cardiovascular outcome data of any omega-3 form. Does not raise LDL. The sole active ingredient in icosapent ethyl.

Icosapent ethyl (Vascepa). A prescription drug containing 96% pure EPA at 4 g/day — the only omega-3 product with FDA approval for cardiovascular risk reduction.

IFOS (International Fish Oil Standards). A third-party program that tests omega-3 products for purity, potency, and freshness, with results at ifos.com.

Number needed to treat (NNT). How many patients must be treated for one to benefit. REDUCE-IT’s NNT of about 21 over 4.9 years means treating about 21 high-risk patients prevented one major cardiovascular event.

Triglycerides. Fats in the blood associated with cardiovascular risk when elevated. Omega-3s lower them reliably at adequate doses — their most consistent effect, though not one that automatically reduces events.

VLDL (very-low-density lipoprotein). The particles the liver releases to carry triglycerides. Reducing VLDL output is a main way omega-3s lower triglycerides.

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