What is the omega-3 index?

Educational information only, not medical advice. Please talk with your physician before changing your diet, taking supplements or ordering lab tests, especially if you are pregnant, take blood thinners or have a medical condition.

The omega-3 index is the percentage of two omega-3 fats, EPA and DHA, in the membranes of your red blood cells. Researchers William Harris and Clemens von Schacky proposed it in 2004 ^[1].

Red-cell levels reflect long-term intake, so the index shows your habits over time rather than your last meal ^[1]. A single dose of fish oil raises plasma (the liquid part of blood) within hours, but it leaves the red-cell level essentially unchanged ^[2]. That's why the index is measured in red cells.

What the numbers mean ^[1][3]:

In a study comparing seven countries, groups from Japan, South Korea and Alaska averaged in the desirable range, while the US group averaged low ^[3]. The authors note that most samples came from the US and that the groups weren't nationally representative.

Why cell membranes? DHA in particular is a very flexible molecule. Laboratory studies show that it changes basic properties of cell membranes, such as their "fluidity" and permeability ^[4]. That helps explain why the index is biologically interesting, but it doesn't by itself prove a health benefit.

The Japanese reference point

Japan is the usual reference for a population that eats fish regularly. A study of RBC fatty acids from seven countries (167,347 individuals) found that only the cohorts from Japan, South Korea and Alaska had a mean Omega-3 Index in the desirable (>8%) range. The US, Canada, Italy and Germany were all classed as low ^[3]. The authors caution that these were cohorts of convenience, some of them small, and that 93% of the samples were from the US ^[3]. Harris has argued, using data from the Japan Public Health Center Study, that target Omega-3 Index levels may need to be redefined ^[17].

Questions? Email omega3@rome.md