Best omega-3 supplement in the UK: how much omega-3 per day, EPA and DHA, and which form to choose

What omega-3 does: EPA and DHA

Omega-3s are a family of fatty acids. Two matter most: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). DHA is part of the cell membranes in the brain and retina. Together, EPA and DHA affect blood triglycerides and inflammation.

A third omega-3, ALA, comes from flaxseed, chia and walnuts. Your body converts it to EPA and DHA poorly, at under 15%, and very little ends up as DHA. That’s why flaxseed oil can’t replace fish.

Do you need an omega-3 supplement?

Maybe not. NHS advice is at least two portions of fish a week, one of them oily, such as salmon, mackerel, herring, sardines or trout. A portion is about 140 g. If you eat that, you probably don’t need a supplement.

A single portion of salmon or herring gives about 3 g of EPA+DHA. That’s more than EFSA’s 250 mg a day for a whole week. A standard fish oil softgel gives about 0.3 g.

Limits on oily fish apply to some groups. Women who are pregnant, breastfeeding or may become pregnant should have no more than two portions a week. A supplement makes sense if:

• You rarely or never eat oily fish.
• You’re vegetarian or vegan (choose algae oil).
• A doctor has advised it, for example for high triglycerides.

How much omega-3 per day, and the “1,000 mg” trap

The big “Fish Oil 1000 mg” on the front catches plenty of people out. It’s the weight of all the oil in the capsule, and omega-3s are only part of it. Find the EPA and DHA lines on the label and add them up.

Watch the serving size. If the panel says “Serving size: 2 softgels”, the EPA+DHA figure is for two capsules. Compare the price per gram of EPA+DHA, not per capsule. To work out how many fish oil capsules a day your bottle needs, use our omega-3 dose calculator.

Fish oil forms: triglyceride vs ethyl ester, krill and algae

• Triglycerides (TG) and re-esterified triglycerides (rTG). The natural form of dietary fat. rTG concentrates pack a lot of omega-3 into a capsule and are well absorbed.
• Ethyl esters (EE). A form created during concentration. Cheaper, and slightly less well absorbed. Any form raises blood EPA and DHA, especially with a fatty meal.
• Phospholipids (krill oil). Absorption may be similar or slightly better, but a capsule typically holds only 100–250 mg of EPA+DHA, so the price per gram is high.
• Microalgae oil. A source of DHA, sometimes EPA too, for vegans and vegetarians. Fish get their omega-3s from algae in the first place.

If the label doesn’t state the form, it’s usually ethyl esters or standard triglycerides. Tap through a sample panel to see how the form, source and serving appear on a bottle:

Freshness and purity

Omega-3s oxidise easily. Rancid fish oil causes unpleasant burps and may lose its benefit.

• Look for independent certification: IFOS (tests oxidation, heavy metals and omega-3 content), USP or NSF.
• A strong fishy smell when you open the bottle is a reason to return it.
• Store unopened bottles somewhere cool and dark. Once opened, follow the label, which often means the fridge.
• Enteric-coated capsules reduce fishy burps.

Fish oil and the heart: what trials show

The evidence is mixed. Don’t overrate the supplement.

• In the VITAL trial, 1 g of omega-3 a day in people without heart disease did not lower the overall risk of major cardiovascular events.
• High prescription doses (several grams a day in drug form) lower triglycerides. Doctors use them in people at high cardiovascular risk.
• A 2021 meta-analysis linked omega-3 supplements to a small rise in atrial fibrillation risk, higher above 1 g a day. Most participants were older people with heart disease or at risk of it.

If you don’t eat fish, 250–500 mg of EPA+DHA a day is a sensible substitute. Save high doses “for the heart” for when a doctor prescribes them.

Fish oil side effects and who should be careful

• Blood thinners (warfarin, clopidogrel and others). Studies of 3–6 g a day didn’t show a major effect on warfarin, but INR checks are advised with high doses. Tell your GP or anticoagulation clinic.
• Heart rhythm problems. Talk to your cardiologist first.
• Fish or seafood allergy. Choose algae oil. A shellfish allergy rules out krill oil.
• Pregnancy. The NHS advises avoiding fish liver oil supplements unless your GP recommends them, because they contain a lot of vitamin A. Ask your midwife before taking any omega-3 supplement.
• Before surgery, doctors sometimes ask you to stop high-dose omega-3.

EFSA advises an extra 100–200 mg of DHA a day in pregnancy, on top of the usual 250 mg of EPA+DHA. Oily fish, within the NHS limit of two portions a week, is the simplest way to get it.

How to choose the best omega-3 supplement in the UK

1. Add up EPA and DHA per serving. For prevention, 250–500 mg is enough.
2. Work out the price per gram of EPA+DHA, which is fairer than the price per bottle.
3. Prefer TG or rTG, or take any form with a fatty meal.
4. Look for IFOS, USP or NSF. Vegans should choose algae oil.
5. Compare makers in our supplement brands section rather than trusting “1000 mg” on the front.

More on reading the panel in our label guide. For another popular “energy” supplement, see our guide to vitamin B complex.