Définition
The Omega-3 Index measures EPA + DHA as a percentage of total fatty acids in red blood cell membranes. It reflects tissue omega-3 status over approximately 3 months, making it more informative than plasma measurements. Optimal is above 8%; most people testing are below 4%.
The Omega-3 Index was developed by William Harris and Clemens von Schacky in 2004 as a tissue-reflective marker of omega-3 status. Rather than measuring transient plasma levels (which fluctuate with recent meals), it measures the percentage of red blood cell membrane fatty acids that are EPA + DHA. Because red blood cells live approximately 120 days, this reflects the 3-month average omega-3 intake integrated across all tissues.
The clinical significance is substantial. Higher Omega-3 Index correlates with: lower sudden cardiac death risk, slower telomere shortening, reduced inflammation, better cognitive aging, lower all-cause mortality, and slower epigenetic aging on multiple clocks. Framingham data showed that individuals with an Omega-3 Index above 8% had substantially lower all-cause mortality than those below 4%.
Target ranges: optimal is above 8%; 4–8% is intermediate; below 4% is a clear deficiency. Modern Western diets, with their high linoleic acid intake and low seafood consumption, produce widespread low Omega-3 Index values — most untested people are in the 3–5% range.
The correction is straightforward and predictable. Oily fish consumption 2–3x weekly typically moves the Omega-3 Index into the 6–8% range. For those unable or unwilling to consume enough fish, supplementation at 2–3g daily of combined EPA + DHA reliably achieves 8%+ within 3–4 months. The form matters modestly — triglyceride-form and ester-form omega-3 products have comparable clinical outcomes; algae-based DHA is effective for plant-based eaters.
For women specifically, higher Omega-3 Index is associated with reduced perimenopausal hot flash severity, lower depression risk, better cognitive aging, and slower biological aging on epigenetic clocks. It is also relevant during pregnancy, when DHA demands spike. Testing is inexpensive (typically $45–75) and provides a useful feedback loop for adjusting intake.
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