Omega-3 index

The Omega-3 index is a blood test. It is the combined amount of two omega-3 fats, EPA and DHA, as a percentage of all the fatty acids in your red-blood-cell membranes. Because red cells live about 120 days, the index reflects your average omega-3 intake over roughly 2 to 4 months. That is an advantage over plasma tests, which only capture recent diet. Harris and Von Schacky (2004) proposed it as a new risk marker for heart-disease death. They set a desirable zone at 8% or higher, and a high-risk zone at 4% or lower. Most adults in Western countries fall between 4% and 6%. Many prospective studies have found that a higher Omega-3 index goes with lower heart and all-cause death, on top of standard lipid risk factors. A 2007 review by Harris pulled this together and strengthened the case. The index is analytically standardized through a certified lab method. But it remains a risk marker, not a proven causal factor. Omega-3 supplement trials have given mixed heart results, so the link cannot yet be called conclusively causal in all populations.

Last reviewed: June 22, 2026

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