Omega-3 Index
The blood biomarker that measures your real EPA and DHA reserve
Definition
The Omega-3 Index is a biomarker that measures the percentage of EPA + DHA (the two long-chain omega-3 fatty acids) relative to total fatty acids in red blood cell membranes. Unlike a one-off blood test, it reflects a stable, weeks-long tissue omega-3 status that is not skewed by your last meal. An index of ≥8% is associated with lower cardiovascular risk and lower all-cause mortality; below 4%, the risk of sudden cardiac death rises sharply, making it one of the most actionable nutritional biomarkers.
Detailed explanation
The Omega-3 Index was proposed by William S. Harris and Clemens von Schacky in 2004 (Preventive Medicine) as an independent, modifiable cardiovascular risk factor. It is measured in the red blood cell membrane because erythrocytes turn over slowly (~120 days), making it a stable long-term marker of omega-3 status — analogous to how HbA1c reflects months of blood glucose.
The evidence is consistent: in the Framingham Heart Study, higher erythrocyte EPA+DHA levels were inversely associated with total mortality and incident cardiovascular disease. UK Biobank analyses show that an unfavorable omega-6/omega-3 ratio predicts greater all-cause, cancer, and cardiovascular mortality. The target range is generally cited as 8-12%.
The index is directly actionable: increasing oily-fish intake or supplementing with EPA/DHA raises the value within weeks. The response is individual — it depends on dose, adiposity, absorption, and genetics — so measuring before and after is the correct way to titrate dose rather than supplementing blind.
Scientific sources
- PubMed — Cardiovascular risk and the omega-3 index (von Schacky, Harris; J Cardiovasc Med 2007)
- PubMed — Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and incident CVD: The Framingham Heart Study (Harris)
- PubMed — Higher plasma omega-6/omega-3 ratio associated with greater all-cause, cancer, and cardiovascular mortality: UK Biobank cohort
- PubMed — The omega-3 index: from biomarker to risk marker to risk factor (Harris)
Related terms
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