Omega-3 labels are dominated by two abbreviations: EPA and DHA. Understanding what they are — and how much of each you actually need — is the key to reading a fish oil properly. This guide explains both, with the authorised claims stated correctly.
For transparency: EPA and DHA are omega-3 fatty acids that do carry authorised UK health claims at specific daily intakes, so we can state those accurately. We won't stretch them beyond what's authorised.
What are EPA and DHA?
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two long-chain omega-3 fatty acids found in oily fish and fish oil. They're the forms of omega-3 your body uses most readily — distinct from ALA, the shorter-chain omega-3 found in plant foods like flaxseed, which the body converts to EPA/DHA only inefficiently. When people talk about the benefits of "omega-3", they almost always mean EPA and DHA.
What's the difference between EPA and DHA?
They're related but have different authorised roles:
- EPA and DHA together contribute to the normal function of the heart (at a daily intake of 250mg).
- DHA specifically contributes to the maintenance of normal brain function and the maintenance of normal vision (at a daily intake of 250mg DHA).
- DHA is also a structural component particularly concentrated in the brain and the retina of the eye.
So EPA is most associated with the heart claim (alongside DHA), while DHA carries the additional brain and vision claims. A good fish oil provides meaningful amounts of both. We cover the heart side in best fish oil for heart health.
How much EPA and DHA do you need a day?
The authorised claims give clear reference points: 250mg of EPA + DHA for the heart claim, and 250mg of DHA for the brain and vision claims. Many general health authorities suggest a couple of portions of oily fish weekly as a dietary target. The practical issue is that lower-strength fish oils may contain surprisingly little actual EPA/DHA per capsule — which is why dose matters.
Why fish oil dose matters
Here's the honest catch with fish oil: a "1000mg fish oil" capsule is not 1000mg of EPA/DHA — that's the weight of the oil, of which EPA/DHA is only a fraction. Low-strength products can contain only a small amount of active omega-3 per capsule, meaning you'd need several to reach a meaningful intake. Always read the EPA and DHA figures, not just the total oil weight. Our high-strength Omega-3 provides 1040mg EPA and 692mg DHA per serving precisely so the active amounts are meaningful.
The takeaway
EPA and DHA are the two active long-chain omega-3s; EPA+DHA support normal heart function (250mg) and DHA additionally supports normal brain function and vision (250mg); and the number that matters on a label is the EPA/DHA content, not the total oil weight. For sourcing and timing, see fish oil vs algae and when to take it; for the full picture, our omega-3 guide.
Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication (including blood thinners) or managing a medical condition, speak to your GP or pharmacist before starting a new supplement. Signed, Dr. Miron, Founder of Pure Vitamins UK.
