Omega-3
The fats from oily fish, taken for the heart, the mind and the joints.
- Heart health
- Mood
- Blood fats
- Joints and inflammation
- Pregnancy
- Memory with age
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is omega-3?
Omega-3 is the family of fats that oily fish are famous for. Two of them, EPA and DHA, are the ones the body wants most: they are built into the membranes of every cell, with the brain, eyes and heart holding the most. A third, ALA, comes from plants such as flax and walnuts, and the body converts only a small share of it into EPA and DHA. Supplements come as fish oil, krill oil, cod liver oil or algae oil (the vegan source), and the number that matters on the label is the combined EPA and DHA per capsule, not the total oil. It is one of the most widely taken supplements in the UK, mostly for the heart and the mind.
Why do people take omega-3?
Heart health
The thinking. Populations that eat a lot of oily fish have long been noted for lower rates of heart disease, and EPA and DHA affect several things that matter to the heart: blood fats, heart rhythm and the lining of blood vessels. Taking fish oil for the heart is the oldest and still the commonest reason.
What research has found. Large randomised trials and reviews measured heart attacks, strokes and deaths from heart disease in adults with or at risk of heart disease. Most recent trials found no clear reduction in these events at ordinary doses, while some earlier reviews, and one trial of a high dose of purified EPA in people with raised triglycerides, found fewer events. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Mood
The thinking. DHA is a major building block of brain cell membranes, and EPA shapes the inflammatory signalling that has been linked with low mood, so people take omega-3 for mood, particularly through the darker months, and researchers have tested it alongside usual care for depression.
What research has found. Three meta-analyses of randomised trials, mostly in adults with depression, found lower depression scores with omega-3 than with placebo, and the effect was clearest with products that were mostly EPA rather than DHA. This is one of the best-studied uses, and several reviews of trials broadly agree.
Blood fats
The thinking. EPA and DHA lower the amount of triglyceride the liver sends into the blood, and high triglycerides are one of the numbers a GP watches. This is the effect with the least argument about it.
What research has found. Meta-analyses of randomised trials in adults with metabolic conditions consistently found lower triglycerides with omega-3; effects on cholesterol and on whether people went on to develop diabetes were less clear. A fair body of trials has looked at this, and most point the same way.
Joints and inflammation
The thinking. EPA and DHA are turned into signalling molecules called resolvins and protectins, whose job is to switch inflammation off once it has done its work. That is the reasoning behind taking fish oil for stiff, sore joints and general aches.
What research has found. An umbrella review pooling 32 meta-analyses, in adults with a wide range of conditions, found lower levels of C-reactive protein and two other blood markers of inflammation with omega-3. Joint pain itself was not one of the outcomes in the studies we graded. Research here is still young: a few studies so far, mostly pointing the same way.
Pregnancy
The thinking. DHA is laid down in a baby’s brain and eyes fastest in the last third of pregnancy, and the mother’s stores supply it, so omega-3 is widely taken in pregnancy and often included in pregnancy multivitamins.
What research has found. A large Cochrane review of trials in pregnant women found fewer preterm births and fewer low-birthweight babies with omega-3, but no clear difference on several other outcomes it measured; a trial that followed the children found less wheeze and asthma in early childhood. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
Memory with age
The thinking. DHA levels in the brain fall with age, so a lot of people take omega-3 in later life in the hope of keeping their memory sharp.
What research has found. Two large randomised trials in older adults, one in people with memory complaints, measured thinking and memory over two to three years and found no clear difference in the rate of decline between omega-3 and placebo. Only a few studies have measured this so far, though they mostly agree.
What does omega-3 do in the body?
Once eaten, EPA and DHA are packed into the membranes of cells throughout the body, and the more you take in, the more of your membranes are made of them rather than of the omega-6 fats that come from vegetable oils. That changes how flexible membranes are and, more importantly, which signalling molecules a cell can make when it is stressed or injured.
From omega-6 fats the body makes molecules that start inflammation; from EPA and DHA it makes resolvins and protectins, which bring inflammation to a close. That balance is the thread running through most of the reasons above, from the heart and blood vessels to mood and joints. Because the body converts only a few per cent of plant ALA into EPA and DHA, fish, krill and algae oils are the direct route.
What do people say about taking omega-3?
These are anecdotes people have shared, not evidence.
What people like
- The people who have stuck with omega-3 for years very commonly say they take it on trust for long-term health rather than because they feel anything day to day, and seem content with that bargain.
- Some long-standing users say their low mood in the darker months feels easier to live with, and some with dry, gritty eyes say their eyes feel more comfortable; in both cases the surest sign was how they felt after letting it lapse.
- A minority on a fairly hefty daily dose for years say their joints and general aches feel less troublesome, and a few mention blood-test numbers that pleased them.
- Vegetarians and vegans on algae oil often report feeling well on it, and people who moved to krill oil say the smaller capsules and milder aftertaste made it far easier to keep up.
Common complaints
- Very commonly, people admit they honestly cannot tell any difference on or off it, and parents who tried it for a child’s concentration often report no change at all.
- Fishy repeating and a fish taste that hangs around for hours is the single most common complaint, and enough to put some people off fish oil for good.
- Extra-strength capsules are described as huge and awkward to swallow, and children frequently refuse them, so the bottle ends up as an expensive dust collector.
- Cost is a recurring grumble, especially for krill oil and high-strength products, along with worries about old oil going rancid and about mercury or farmed-fish quality.
How people take it
- The people who report feeling anything are nearly always on a fairly high dose taken consistently for months. The shared rule of thumb is to read the back of the pack for combined EPA plus DHA rather than the headline fish oil amount, with around 500 mg per capsule offered as the mark of a decent product.
- For concentration and mood people are pointed towards products with two to three times more EPA than DHA, with the frank warning to expect only a modest change after two to three months.
- Nobody describes a quick effect: two to three months is the usual figure, and a striking number say the clearest signal came when they stopped rather than when they started.
- Keep capsules in the fridge to slow the oil going off, take them with a meal that has some fat in it, and choose smaller krill capsules or a liquid if big softgels are a struggle. Algae oil is the default for vegetarians and vegans, and a fair few would rather eat tinned sardines than take capsules at all.
Read from these public discussions:
- Do you get enough Omega 3? (Mumsnet, 2025)
- Omega 3 recommendation please (Mumsnet, 2022)
- ADHD and Omega 3 (Mumsnet, 2023)
- Krill Oil Caps...the better oil supplement?? (AnandTech forums, 2021)
- Fish oil (AnandTech forums, 2018)
- is omega3 really working for u? (Dry Eye Zone forum, 2007)
What forms of omega-3 are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Fish oil | Oil from oily fish or fish-oil-derived esters. | 260 mg to 2.25 g |
| Krill oil | Oil from krill, a small shrimp-like crustacean. | 88 mg to 226 mg |
| Algae oil (vegan) | Oil from algae; the main vegan source. | 250 mg to 600 mg |
| Cod liver oil | Oil from the liver of cod, rather than fish body tissue. | not in our price tables yet |
What else is worth knowing about omega-3?
- Labels quote EPA and DHA per capsule or serving separately from the total oil; a 1,000 mg fish oil capsule often holds well under half that as EPA and DHA, which is the figure our price tables compare.
- Trials tested doses from about 0.5 g to more than 5 g of EPA and DHA a day; the mood trials mostly used EPA-rich products.
- One large review found a hint of worse outcomes above 4.4 g a day.
- Cod liver oil carries vitamins A and D as well as omega-3, which its label will list; fish body oils do not.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (22 studies)
- Omega-3 and omega-6 polyunsaturated fatty acids: Dietary sources, metabolism, and significance - A review. (2018, review)
- Omega-3 Polyunsaturated Fatty Acids and Their Health Benefits. (2018, review)
- Omega-3 fatty acids and inflammatory processes: from molecules to man. (2017, review)
- Effect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis. (2021, meta-analysis)
- Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. (2020, meta-analysis)
- Marine Omega-3 Supplementation and Cardiovascular Disease: An Updated Meta-Analysis of 13 Randomized Controlled Trials Involving 127 477 Participants. (2019, meta-analysis)
- Associations of Omega-3 Fatty Acid Supplement Use With Cardiovascular Disease Risks: Meta-analysis of 10 Trials Involving 77 917 Individuals. (2018, meta-analysis)
- Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: a systematic review and meta-analysis. (2012, meta-analysis)
- Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. (2019, randomised trial)
- Effect of Long-term Marine ɷ-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-analysis. (2021, randomised trial)
- n-3 fatty acids and cardiovascular outcomes in patients with dysglycemia. (2012, randomised trial)
- Efficacy of omega-3 PUFAs in depression: A meta-analysis. (2019, meta-analysis)
- Meta-analysis of the effects of eicosapentaenoic acid (EPA) in clinical trials in depression. (2016, meta-analysis)
- Meta-analysis of the effects of eicosapentaenoic acid (EPA) in clinical trials in depression. (2014, meta-analysis)
- Effects of omega-3 fatty acid supplementation on lipid profiles and glycaemic control: a systematic review and meta-analysis. (2026, meta-analysis)
- Omega-3 fatty acids and cardiometabolic risk: a systematic review and meta-analysis. (2024, meta-analysis)
- Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. (2019, meta-analysis)
- Omega-3 polyunsaturated fatty acids supplementation and inflammatory biomarkers: An umbrella review of meta-analyses of randomized controlled trials. (2022, meta-analysis)
- Omega-3 fatty acid addition during pregnancy. (2018, meta-analysis)
- Fish Oil-Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring. (2016, randomised trial)
- Effect of Long-term Omega 3 Polyunsaturated Fatty Acid Supplementation With or Without Multidomain Intervention on Cognitive Function in Elderly Adults With Memory Complaints (MAPT): a randomised, placebo-controlled trial. (2017, randomised trial)
- Effect of Vitamin D and Omega-3 Fatty Acid Supplementation on Cognitive Function in Older Adults. (2020, randomised trial)
How much does omega-3 cost?
That depends on the form and the pack, so we work out the price of the same dose of every omega-3 product we can find and rank them.