The Omega-3 Index: the blood marker behind your EPA and DHA target

Most nutrition advice about fish oil stops at 'eat more oily fish'. Far more useful is that omega-3 status is directly measurable in your blood — the Omega-3 Index, the percentage of EPA plus DHA in your red blood cell membranes — and that this single number tracks with hard outcomes.

What the Omega-3 Index measures

Harris and von Schacky (2004, Preventive Medicine) proposed the Omega-3 Index as a stable, long-run marker of tissue omega-3 status, less noisy than a one-off plasma reading because red blood cells turn over slowly. An index below 4% is associated with the highest cardiovascular risk; 8% or above sits in the protective range. Later work (Harris et al., 2021) found a low Omega-3 Index predicted all-cause mortality about as strongly as smoking status in some cohorts.

An Omega-3 Index under 4% carried a mortality signal comparable to smoking in some cohorts — and unlike your genes, it moves with what you eat.

How much EPA and DHA it actually takes

The cardio-protective FLOOR is roughly 250 to 500 mg of combined EPA and DHA per day — the amount in about two portions of oily fish a week. That is a minimum, not a ceiling. Therapeutic doses used for elevated triglycerides and inflammation run far higher: the REDUCE-IT trial (Bhatt et al., 2019, NEJM) used 4 g/day of a purified EPA ester and cut major cardiovascular events by around 25% in high-risk patients. Plant omega-3 (ALA from flax, chia, walnuts) helps but converts to EPA and DHA inefficiently — often under 10% (Burdge, 2006) — so it does not replace marine sources.

How Misi connects intake to the marker

Misi's Insights includes an EPA + DHA per-day chart with the 250–500 mg cardio floor and the 2–4 g therapeutic band drawn in, computed from the marine omega-3 content of everything you log. If you have entered lab results, the Labs tab goes one step further and bridges your average EPA+DHA intake against your measured Omega-3 Index — closing the loop between what you eat and what your blood shows, and flagging when your intake is nowhere near what your index needs.

The practical takeaway

If you eat oily fish two or three times a week you are probably near the floor already. If you rarely eat fish, this is one of the highest-yield, best-evidenced supplement decisions available — and one of the few where a cheap blood test tells you objectively whether it is working.

Misi is a coaching and wellness platform, not a medical service. High-dose omega-3 can affect bleeding and interacts with some medications; discuss therapeutic doses with your doctor.