Omega-3 Index

The Omega-3 Index measures the percentage of EPA and DHA in your red blood cell membranes. Because red cells live for about 120 days, the number reflects your omega-3 intake over the previous three to four months rather than what you ate this week. That makes it one of the few blood markers that resists being gamed by a single good meal before the draw.

EPA and DHA are structural fats. They sit in the membrane of every cell you have, where they affect how flexible that membrane is and how it passes signals. Your body cannot make them in useful quantities, so the supply comes almost entirely from oily fish, seafood, and supplements. Plant sources such as flax and walnuts provide ALA, which converts to EPA and DHA at a low and variable rate.

A result below 8% means the omega-3 content of your membranes is under the reference range. This is the common finding in Western populations, and it usually reflects intake rather than absorption.

Raising the index takes months, not days. Doses of 1,000 to 1,500 mg per day of combined EPA and DHA, taken for twelve weeks or longer, are what the published dose-response work associates with reaching 8% or above (Dempsey et al., 2023). Triglyceride-form supplements were more bioavailable in that analysis than ethyl ester forms.

For dietary intake, the European Food Safety Authority sets 250 mg per day for DHA. Two to three servings of oily fish per week is the usual food-first route to that figure.

Between 8% and 15% your membranes carry the EPA and DHA content associated with the reference range used on this panel.

Holding the number there is mostly a question of consistency. Intake and index track each other with a lag of about three months, so a period of low intake will show up on a retest one quarter later rather than immediately.

Above 15% is uncommon and generally reflects high-dose supplementation rather than diet alone.

Very high intakes can extend bleeding time, which matters if you take anticoagulant or antiplatelet medication. Digestive effects such as reflux and loose stools are also reported at high doses. If your result is above the range, review your total supplement dose, including any cod liver oil or fortified products you may not be counting.

Discuss a result at either extreme with your practitioner, particularly if you take medication that affects clotting.

Western diets supply a large amount of linoleic acid from seed oils and very little EPA and DHA. The two compete for the same enzymes, so a high linoleic intake makes the conversion problem worse at the same time as fish intake falls.

The result is a population where a low Omega-3 Index is the norm rather than the exception. This is the single marker on the panel where the typical Western result and the reference range are furthest apart.

Oily fish is the most direct route: salmon, mackerel, sardines, herring and anchovies. Two to three servings per week covers the EFSA figure for most people.

Shellfish and roe contribute smaller amounts. Algae-derived DHA is the practical option if you do not eat fish, since it supplies DHA directly rather than relying on conversion from ALA.

Reducing linoleic acid from sunflower, corn and soybean oil helps the ratio from the other direction, and is worth doing alongside rather than instead of raising intake.

Combined EPA and DHA at 1,000 to 1,500 mg per day is the range associated with moving the index into the reference band over twelve weeks or more.

Triglyceride-form fish oil absorbs better than ethyl ester form. Algal oil is the vegan equivalent and is DHA-dominant.

Take it with a meal containing fat. Absorption is meaningfully lower on an empty stomach.