The omega-3 index measures the proportion of EPA and DHA in red blood cell membranes, expressed as a percentage of total fatty acids. Proposed in 2004 by researchers William Harris and Clemens von Schacky, this blood test has become a recognized marker of cardiovascular risk and, more broadly, of longevity. A low score is linked to higher all cause mortality risk; a high score reflects regular intake of fatty fish.
In brief – The omega-3 index is a blood biomarker that measures the share of EPA and DHA, two long chain omega-3 fatty acids, in red blood cell membranes, expressed as a percentage of total fatty acids. An index at or below 4% signals high cardiovascular risk, while an index at or above 8% falls in the protective zone identified by Harris and von Schacky in 2004. A 2018 study of the Framingham cohort found that participants in the highest quintile (above 6.8%) had a 34% lower all cause mortality risk than those in the lowest quintile (below 4.2%), over a median follow up of 7.3 years. The score mainly reflects fatty fish consumption: the Western average often falls below the protective thresholds.
Definition: what exactly does the omega-3 index measure?
The term covers two markers measured together: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), two long chain omega-3 fatty acids of mainly marine origin. The calculation starts from a blood sample, a capillary fingerstick or a standard blood draw, analyzed in a specialized laboratory: EPA plus DHA as a share of total fatty acids present in the red blood cell membrane, multiplied by 100.
Unlike a standard plasma test, which reflects the diet of the past few days, this red blood cell marker captures average intake over the past three to four months, the lifespan of a red blood cell. This stability makes it a more reliable indicator than a self reported food questionnaire.
Mechanism: why this marker influences cardiovascular risk
EPA and DHA become incorporated into the lipid bilayer of cell membranes, where they alter membrane fluidity and the production of inflammatory mediators. The liver converts only a small amount of alpha linolenic acid (ALA), a plant precursor found in walnuts and canola oil, into EPA and DHA; the conversion rate rarely exceeds 5 to 10%. Most of the supply therefore comes directly from marine sources.
Several mechanisms link a high index to reduced cardiovascular risk:
- Lower production of pro-inflammatory cytokines, through a metabolic pathway that competes with arachidonic acid
- Stabilization of cardiomyocyte membranes, associated with a lower risk of arrhythmia
- Moderate reduction in circulating triglycerides
- An effect on platelet membrane fluidity and aggregation
These mechanisms align with the literature on inflammaging, the chronic low grade inflammation that accompanies aging and accelerates the loss of organ function (Franceschi & Campisi, 2014).
What the science says about the omega-3 index and longevity
Harris and von Schacky proposed the concept in 2004 in the journal Preventive Medicine, defining an index at or above 8% as the cardiovascular protection zone and an index at or below 4% as the high risk zone (Harris & von Schacky, 2004).
This hypothesis was tested in the Framingham cohort. Among participants followed for a median of 7.3 years, those in the highest quintile (above 6.8%) had a 34% lower all cause mortality risk than those in the lowest quintile (below 4.2%), and a 39% lower risk of an incident cardiovascular event (Harris et al., 2018).
A later analysis of the same cohort, published in 2021, compared the predictive power of this marker and other red blood cell fatty acids to that of standard cardiovascular risk factors: age, smoking, cholesterol, blood pressure. The fatty acid based model showed predictive ability comparable to standard risk factors for all cause mortality (McBurney et al., 2021).
These results come from observational cohort studies: they show a robust association, replicated across several studies, not proof of direct causation established by a large randomized trial on mortality.
In practice: who benefits from knowing their score
This blood marker mainly interests people monitoring their cardiovascular risk or wanting to objectively assess their fatty fish intake, alongside a broader blood panel such as the Bortz method for biological age, or the phenotypic age biomarkers. The test is not covered by health insurance in France; it is prescribed mainly through private laboratories or as part of preventive medicine follow up, one focus area of UltraSante’s longevity pillar.
The table below summarizes the score zones and their usual interpretation.
| Zone | Value | Interpretation |
|---|---|---|
| High risk | ≤ 4% | Very insufficient EPA and DHA intake, increased cardiovascular risk |
| Intermediate zone | Between 4% and 8% | Partial intake, room for improvement through diet |
| Protection zone | ≥ 8% | Regular fatty fish intake, associated with reduced mortality |
Western populations most often fall between 4 and 5%, compared with 8 to 11% in Japan, where fish consumption is markedly higher. This contrast fuels part of the literature comparing the fish richest in omega-3s to species to favor or limit because of mercury contamination.
Protocol: how to improve your score
No official protocol sets a testing frequency for the general population. The following benchmarks help outline a reasonable approach:
- Eat fatty fish (salmon, mackerel, sardine, herring) twice a week, in line with NHS dietary guidance
- Favor smaller species to limit exposure to mercury and organic pollutants
- Retest the score three to four months after a dietary change, the time it takes for red blood cells to turn over
- Discuss possible supplementation with a healthcare professional in case of very low intake or known cardiovascular disease
A score that rises from 4% to 8% over a few months reflects a lasting dietary change, not the one time effect of a fish meal the day before the blood draw.
Frequently asked questions about the omega-3 index
How should I interpret a low omega-3 index?
A score at or below 4% signals insufficient EPA and DHA intake. In the Framingham cohort, this zone is associated with higher all cause mortality risk than the highest quintile. This finding remains a statistical cohort association, not an individual diagnosis: it should be interpreted alongside a full cardiovascular workup, never in isolation.
What is the difference between the omega-3 index and a standard plasma test?
A standard plasma test reflects the diet of the past two to three days, because circulating lipids turn over quickly. This marker instead measures fatty acids incorporated into red blood cell membranes, whose lifespan is close to 120 days. It gives a more stable picture of average EPA and DHA intake over several months.
Why does the omega-3 index vary so much between countries?
Fatty fish consumption varies widely with national dietary habits. Japanese populations, who eat a lot of fish, show an average score of 8 to 11%, compared with 4 to 5% in most Western countries, where fatty fish consumption remains occasional.
Can you get your omega-3 index measured in France?
The test is not listed among procedures covered by health insurance in France. It is available through certain private laboratories or as part of preventive medicine follow up, on prescription or by direct request depending on the laboratory. The sample, a capillary blood drop or a standard blood draw, is then analyzed by chromatography.
Medical disclaimer. The information provided here is for informational purposes only and does not constitute medical advice. It does not replace a consultation. Ask a healthcare professional before changing your diet, taking dietary supplements or starting a new practice, especially if you have a medical condition, are pregnant or are under treatment. Dietary supplements do not replace a balanced diet or medical follow up.
