Omega-3 index

The Omega-3 index is a blood biomarker defined as the sum of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) expressed as a percentage of total fatty acids in red blood cell (erythrocyte) membranes. Because erythrocytes have a lifespan of approximately 120 days, the index reflects average long-term omega-3 intake over roughly two to four months — an advantage over plasma measurements, which capture only recent dietary exposure. Harris and Von Schacky (2004) proposed the index as a novel risk factor for coronary heart disease mortality, defining a desirable zone of ≥8% and a high-risk zone of ≤4%; most adults in Western populations fall between 4% and 6%. Multiple prospective cohort studies have reported inverse associations between the Omega-3 index and cardiovascular and all-cause mortality, independent of conventional lipid risk factors; a 2007 review by Harris synthesized this evidence and strengthened the case for clinical utility. The index is analytically standardized through a certified laboratory methodology, but it remains a risk marker rather than a risk factor in the causal sense — omega-3 supplementation trials have yielded heterogeneous cardiovascular outcomes, so the association cannot yet be interpreted as conclusively causal in all populations.