What it is

The Omega-3 Index is the percentage of EPA + DHA in your red blood cell membranes — a stable, months-long marker of omega-3 status measured with a simple finger-prick test.

Why it matters for longevity

Pooling 17 prospective cohorts, people in the highest quintile of circulating long-chain omega-3 (EPA, DPA, DHA) had an all-cause mortality hazard ratio of about 0.82–0.85 versus the lowest. The ≥8% Omega-3 Index target comes from earlier CHD-death work (Harris & von Schacky 2004), not from that 2021 pooling — and two large RCTs on this page (VITAL, ASCEND) did not reduce all-cause death.

How to improve it

Eat fatty fish (salmon, sardines, mackerel) 2–3x/week
Consider an EPA/DHA supplement if you don’t eat fish
Re-test after ~4 months to confirm you’ve reached 8%+

Evidence, by endpoint

Endpoint	Grade	Finding
CHD death	C	The 8% Target (Harris 2004) The ≥8% Omega-3 Index target is from earlier CHD-death work, not the 2021 all-cause pooling.
All-cause mortality	C	17 Cohorts (Harris 2021) Highest vs lowest quintile of circulating long-chain omega-3 had all-cause HR about 0.82–0.85.
All-cause mortality	C	34% Lower at Index >6.8% (Harris 2018) Framingham Offspring, 2,500 adults, 350 deaths: highest Omega-3 Index quintile (>6.8%) vs lowest (<4.2%) carried 34% lower all-cause mortality and 39% lower incident CVD, adjusted for 18 covariates. Total cholesterol was not significantly associated with either outcome in the same models.
All-cause mortality	A	VITAL: No ACM Benefit From Supplements (Manson 2018) VITAL randomized 25,871 US adults to 1 g/day marine omega-3 or placebo, median 5.3 years. The trial did not meet its primary cardiovascular endpoint (HR 0.92, 0.80–1.06, P=0.24) and all-cause mortality was not reduced (HR 1.02, 0.90–1.15, 978 deaths). A secondary endpoint, total myocardial infarction, was significantly lower with omega-3 (HR 0.72, 0.59–0.90) — supplementing does not reproduce the mortality association seen in Harris’s blood-level cohort studies.
All-cause mortality	A	ASCEND: Same Null Result in Diabetics (Bowman 2018) ASCEND randomized 15,480 adults with diabetes but no known atherosclerotic disease to 1 g/day omega-3 or placebo, mean follow-up 7.4 years. Neither the primary vascular endpoint (8.9% vs 9.2%, rate ratio 0.97, 0.87–1.08) nor all-cause mortality (9.7% vs 10.2%, rate ratio 0.95, 0.86–1.05) differed significantly between groups.
MACE	A	REDUCE-IT’s Positive Result Doesn’t Generalize (Bhatt 2018) REDUCE-IT randomized 8,179 statin-treated patients with elevated triglycerides (70.7% with established cardiovascular disease) to 4 g/day icosapent ethyl — a purified high-dose EPA-only prescription, far above typical fish-oil or Omega-3 Index-range intake — or placebo, median 4.9 years. Unlike VITAL and ASCEND, it met its primary composite endpoint (17.2% vs 22.0%, HR 0.75, 0.68–0.83, P<0.001), including lower cardiovascular death (HR 0.80, 0.66–0.98). Because of the high EPA-only dose and higher-risk population, this should not be generalized to typical dietary omega-3 intake.
All-cause mortality (predictive discrimination)	C	Predicts as Well as Standard Risk Factors (McBurney 2021) Framingham Offspring Cohort, 2,240 adults without prevalent cardiovascular disease, 11 years of follow-up: a panel of 4 red-blood-cell fatty-acid metrics, including the Omega-3 Index, predicted all-cause mortality about as well as a model built from 6 standard clinical risk factors (age, sex, total cholesterol, HDL, hypertension treatment, systolic BP) — C-statistic 0.778 vs 0.777. Adding smoking status and diabetes to the fatty-acid panel improved prediction further (C-statistic 0.790, P<0.01).

What argues against this

Manson et al. 2018 (VITAL, RCT, 25,871 adults, median 5.3 years) is the strongest opposing source: randomizing to 1 g/day marine omega-3 did not reduce all-cause mortality (HR 1.02, 0.90–1.15) or meet the primary cardiovascular endpoint. This directly undercuts the cohort-based claim (Harris 2021, Harris 2018) that higher blood omega-3 levels track lower all-cause mortality, by showing that raising omega-3 intake through supplementation does not reproduce that mortality benefit when tested in a randomized trial; ASCEND (Bowman 2018) found the same null result in diabetics.

Last reviewed 2 September 2026

Evidence

Harris et al. (2021) — Nature Communications
Blood n-3 fatty acid levels and total and cause-specific mortality from 17 prospective studies
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Manson et al. (2018) — New England Journal of Medicine
Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer (VITAL trial)
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Bowman et al. (2018) — New England Journal of Medicine
Effects of n-3 Fatty Acid Supplements in Diabetes Mellitus (ASCEND trial)
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Bhatt et al. (2018) — New England Journal of Medicine
Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE-IT trial)
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Harris et al. (2018) — Journal of Clinical Lipidology
Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and with incident cardiovascular disease: The Framingham Heart Study
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McBurney et al. (2021) — The American Journal of Clinical Nutrition
Using an erythrocyte fatty acid fingerprint to predict risk of all-cause mortality: the Framingham Offspring Cohort
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Harris & Von Schacky (2004) — Preventive Medicine
The Omega-3 Index: a new risk factor for death from coronary heart disease?
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See how omega-3 index fits your full score

See how it fits the 8-metric index in the calculator.

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Educational content only — not medical advice, diagnosis, or treatment. Not a medical device; not FDA evaluated. Consult a qualified healthcare professional about your own health, and call emergency services for urgent symptoms. Full medical disclaimer →