The Omega-3 Index: what it measures and how to read it

The Omega-3 Index may be the most concrete number in a fatty-acid test. It answers a simple question: how much of the fatty acids in your red blood cells are the marine omega-3 fatty acids EPA and DHA?

How the index is defined

The index is the sum of EPA and DHA, given as a percentage of all the fatty acids in red blood cell membranes.[source pending] It is measured in a fatty-acid test, usually from a dried blood spot you take at home.[source pending]

It measures level, not intake. Two people eating the same amount of fish can get different indexes, because absorption and the rest of the diet vary.[source pending]

Why red blood cells

Red blood cells live for about four months.[source pending] The fatty acids in their membranes therefore reflect your diet over the last few months. That makes the index more stable than a measure that swings with what you ate yesterday, and it means you can eat as usual before the test.

What affects the index

• How much EPA and DHA you get, mainly from oily fish and marine oils.[source pending] The calculator below gives a rough estimate of your intake from food.
• How consistently you get it. A habit over months counts for more than a single week.
• How your body absorbs it, which varies from person to person.
• Time. Because cells are replaced gradually, it takes months before a change fully shows. That is why I plan a retest around 120 days after the first.

How to read the number

The laboratory usually gives the index together with a reference range. Use it as a map, not a grade. Read the index together with the omega-6:3 ratio and AA:EPA: the index shows how much EPA and DHA you have, the ratios show the balance against omega-6.

What the index is not

The Omega-3 Index is a measurement of fatty acids. It is not a diagnosis and says nothing about illness. It tells you where you are, not why. Read more about what a test can and can't tell you.

The authorised claims

What the EU has authorised about EPA and DHA is that they contribute to the normal function of the heart with a daily intake of 250 mg EPA and DHA, and that DHA contributes to maintenance of normal brain function and normal vision with 250 mg DHA a day.[European Commission 2012]Official Journal of the European Union · 2012Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and healthEuropean Commission↓ eu-432-2012↗ eur-lex.europa.eu I claim nothing beyond that.

Next step

Knowing your own index takes a test. Take the free 2-minute check to see whether it makes sense for you now, or browse the glossary if your report has words you don't know.

Sources

1. [source pending] Source needed: original definition of the Omega-3 Index (EPA + DHA as % of red blood cell fatty acids)
2. [source pending] Source needed: validation of dried blood spot fatty-acid analysis against venous samples
3. [source pending] Source needed: study on how much EPA+DHA content and absorption vary between supplements and between people
4. [source pending] Source needed: red blood cell lifespan (~120 days) and how fast membrane fatty acids change
5. [source pending] Source needed: Norwegian dietary guidance on fatty fish and food sources of omega-3 (Helsedirektoratet)
6. European Commission. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and health. Official Journal of the European Union (2012).