Omega-3 Index: The Most Important Blood Test You've Never Had

If you've had a cholesterol panel — and most adults have — you've been told your HDL, LDL, and triglycerides. Those numbers matter, but the research over the past decade suggests there's a better predictor of cardiovascular mortality that almost nobody measures: the omega-3 index. The omega-3 index is the percentage of EPA and DHA (the two main marine omega-3 fatty acids) in your red blood cell membranes. It's a stable, long-term measure of your omega-3 status — and it predicts cardiovascular death better than cholesterol.

This guide explains what the omega-3 index is, why it matters, what the optimal range is, how to test it, and how to raise it. For our specific omega-3 supplement recommendations, see our best omega-3 supplements guide.

What is the omega-3 index?

The omega-3 index is the percentage of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) in the fatty acids of your red blood cell (RBC) membranes. It's expressed as a percentage: an omega-3 index of 8% means 8% of the fatty acids in your RBC membranes are EPA+DHA.

Why red blood cells? Because RBCs live for about 120 days, their fatty acid composition reflects your omega-3 intake over the past 3–4 months — a long-term, stable measure. Plasma omega-3 levels, by contrast, fluctuate day-to-day based on what you ate yesterday.

The omega-3 index was developed by William Harris and Clemens von Schacky in 2004. They showed it's a reliable, reproducible biomarker of omega-3 status, and that it predicts cardiovascular mortality better than any single cholesterol measurement.

Why the omega-3 index predicts cardiovascular mortality

Multiple mechanisms explain why higher omega-3 index = lower cardiovascular mortality:

• Anti-arrhythmic: EPA and DHA stabilize the electrical activity of heart muscle cells, reducing the risk of fatal arrhythmias (the most common cause of sudden cardiac death).
• Anti-inflammatory: EPA and DHA are precursors to resolvins, protectins, and maresins — specialized pro-resolving mediators that actively resolve inflammation.
• Triglyceride lowering: omega-3s reduce hepatic triglyceride production, lowering blood triglycerides by 20–30% at therapeutic doses.
• Endothelial function: omega-3s improve the function of the blood vessel lining, reducing arterial stiffness.
• Blood pressure: omega-3s modestly reduce blood pressure (2–3 mmHg systolic at adequate doses).
• Platelet function: omega-3s mildly reduce platelet aggregation (anti-clotting effect, modest).
• Heart rate reduction: omega-3s lower resting heart rate by 2–3 bpm, which is associated with lower cardiovascular mortality.

These mechanisms add up. People with high omega-3 index die less often from cardiovascular causes — and the effect is large enough that the omega-3 index is, in many studies, a stronger predictor of cardiovascular death than LDL cholesterol.

The evidence: how big is the effect?

The key evidence comes from several large cohort studies:

• Harris et al. (2008, Atherosclerosis): analyzed omega-3 index and cardiovascular mortality in multiple cohorts. Found that an omega-3 index above 8% was associated with ~70% lower risk of sudden cardiac death compared to below 4%.
• The Framingham Heart Study (Harris et al. 2018): followed 2,500 adults and found that those in the highest omega-3 index quintile had 33% lower all-cause mortality and 40% lower cardiovascular mortality than those in the lowest quintile. The omega-3 index was a stronger predictor of mortality than cholesterol.
• REDUCE-IT trial (2018): a randomized trial of high-dose EPA (4 g/day) in patients with elevated triglycerides on statins showed 25% reduction in cardiovascular events. (Note: this used a prescription EPA product, Vascepa, not standard fish oil.)
• Meta-analyses: consistently show ~10% reduction in cardiovascular events per 1% increase in omega-3 index.

Not all omega-3 trials have been positive — the ASCEND trial and the VITAL trial showed no significant cardiovascular benefit from low-dose (1 g/day) fish oil in primary prevention. The likely explanation: the dose was too low to move the omega-3 index into the optimal range. The benefit appears at higher doses (2–4 g/day EPA+DHA) and at omega-3 indices above 8%.

What's the optimal omega-3 index? (8–12%)

The omega-3 index has well-defined risk zones:

The target is 8–12%. Most Americans are below 5%. Japanese adults (who eat fish daily) average 9–10% and have the lowest cardiovascular mortality in the developed world. Reaching 8%+ is achievable with supplementation but requires consistent dosing.

How to test your omega-3 index

The omega-3 index requires a specialized test — it's not part of standard bloodwork. Options:

• OmegaQuant: the company founded by William Harris (the co-inventor of the omega-3 index). Offers a finger-prick at-home test for ~$55. This is the gold standard consumer test.
• Other labs: some specialty labs (Quest, LabCorp) offer RBC fatty acid analysis, but you'll need a physician's order.
• Nutritionally focused direct-to-consumer panels: some companies bundle omega-3 index with other nutrition biomarkers.

Test once to establish baseline. If you supplement, re-test after 3–4 months to confirm you've reached the target range. Annual testing is reasonable once you're in the optimal range.

How to raise your omega-3 index

Raising your omega-3 index requires consistent intake of EPA and DHA. The main sources:

• Oily fish: salmon, sardines, mackerel, herring, anchovies — 2–3 servings per week provides ~1–2 g/day EPA+DHA.
• Fish oil supplements: the most practical way to reach therapeutic doses. Our top pick is Nordic Naturals Ultimate Omega:

• Smaller-dose fish oil: for maintenance or those new to supplementation:

• Algae oil (vegan): the only plant-based source of direct EPA and DHA. Vegans, vegetarians, and people who can't tolerate fish oil should use algae oil:

For the full product comparison, see our best omega-3 supplements guide.

Dose: how much EPA+DHA do you need?

Dosing to reach the 8–12% omega-3 index:

• Maintenance dose (general health): 1–2 g/day EPA+DHA combined. Will get most people to 6–8%.
• Therapeutic dose (to reach 8–12%): 2–4 g/day EPA+DHA combined. Most people need this dose to reach the optimal range.
• Cardiovascular risk reduction (per REDUCE-IT): 4 g/day EPA (under medical supervision, particularly for elevated triglycerides).

Important: many fish oil supplements list total fish oil (e.g., 1,000 mg fish oil) but provide only 300–600 mg of actual EPA+DHA. Read the supplement facts panel carefully — what matters is the EPA+DHA content, not the total fish oil weight.

It takes 3–4 months of consistent daily dosing to reach a new steady-state omega-3 index. Don't expect fast changes — this is a long-term biomarker.

Form matters: triglyceride vs ethyl ester vs phospholipid

Fish oil supplements come in three main forms, with different absorption:

• Triglyceride form (TG): the natural form found in fish. Best absorption (~70% better than ethyl ester). Most premium supplements use this form.
• Ethyl ester form (EE): concentrated form created by esterification. Cheaper, slightly lower absorption, but still effective. Most mass-market fish oils use this form.
• Phospholipid form (krill oil): found in krill oil. Lower total EPA+DHA per dose but better absorption per gram. Some evidence krill oil is more effective than fish oil at lower doses, but the cost per gram of EPA+DHA is higher.

Practical recommendation: buy a triglyceride-form fish oil with high EPA+DHA content per serving. Nordic Naturals Ultimate Omega (above) is triglyceride form and a good value.

What about plant-based omega-3 (ALA)?

Plant foods contain ALA (alpha-linolenic acid) — flaxseed, chia, walnuts, hemp. The body can convert ALA to EPA and DHA, but the conversion rate is poor: roughly 5–10% to EPA, less than 1% to DHA. So while ALA is healthy and you should eat ALA-rich foods, it's not a reliable way to raise your omega-3 index.

For people who don't eat fish, the practical solution is algae oil — which provides direct EPA and DHA without animal sources. Algae is actually where fish get their omega-3 in the first place. Nordic Naturals Algae Omega (above) is our top vegan pick.

For more on plant-based longevity, see our longevity diet guide.

The bottom line

The omega-3 index is one of the strongest predictors of cardiovascular mortality — stronger, in many studies, than cholesterol. Most adults are below 5% (high risk); the target is 8–12% (optimal). The only way to know your omega-3 index is to test it (OmegaQuant is the standard at-home test, ~$55). To raise it: eat oily fish 2–3 times per week and supplement with 2–4 g/day of EPA+DHA from a quality fish oil (or algae oil if vegan). Re-test after 3–4 months to confirm you've reached the target range.

Of all the supplements we recommend for longevity, omega-3 has among the strongest evidence. Pair with regular exercise, Mediterranean-style diet, good sleep, and the other foundational longevity interventions for the full benefit. See our beginner protocol and supplement stack guide for the broader framework.