What Is Omega-3? ALA, EPA and DHA, How Much You Need and Where From

Omega-3 is a family of polyunsaturated fats the body cannot make from scratch: ALA, the plant omega-3 in flaxseed, chia, walnuts and rapeseed oil, and the two long-chain omega-3s, EPA and DHA, from oily fish and algae. ALA is the strictly essential one; most adults turn only about 5% of it into EPA and almost none into DHA, which is why "omega-3" on a label can mean three different things.¹ The GB register ties its wording to daily amounts: 250 mg of EPA and DHA for the normal function of the heart, 250 mg of DHA for normal brain function and vision, 200 mg more DHA in pregnancy, 2 g of ALA for normal blood cholesterol.² The trials add a second layer: triglycerides fall with dose, coronary events fall a little at about 1 g a day, mortality does not change, and above 1 g a day the risk of atrial fibrillation rises, so more is not better.^{3, 4}

• The yardstick: 250 mg EPA+DHA (heart), 250 mg DHA (brain, vision), 200 mg extra DHA in pregnancy, 2 g ALA (cholesterol)
• The trials: triglycerides down about 15%; atrial fibrillation up with dose
• How much: two portions of fish a week, one oily; read mg of EPA and DHA, not mg of oil

Sources checked on 29 October 2026.

What is omega-3?

Three omega-3 fats matter in food. Alpha-linolenic acid (ALA, 18 carbons) comes from plants: flaxseed (linseed), chia, hemp, walnuts, rapeseed oil and soya. Eicosapentaenoic acid (EPA, 20 carbons) and docosahexaenoic acid (DHA, 22 carbons) are made by marine algae and concentrated up the food chain into oily fish; algal oil takes them straight from the algae. Only ALA is strictly essential: the body can lengthen it into EPA and DHA but cannot make it. The catch is that most adults convert about 5% of ALA to EPA and under 1% to DHA; in tracer studies young men made no detectable DHA, while young women did better, about a fifth to EPA and 9% to DHA.^{1, 5, 26} Does flaxseed oil contain omega-3, 6 and 9 covers conversion in detail; the differences between omega-3, 6 and 9 sets the three families side by side.

What does omega-3 do in the body?

EPA and DHA are built into cell membranes, DHA above all in the brain and retina, and in the liver they lower the output of triglyceride-rich particles, which is why triglycerides fall with dose. The GB register allows this wording only at a stated daily intake, and those amounts are a yardstick for any label.²

A product supplying less than the right-hand column may not carry the wording, and every wording is about maintaining normal function, not improvement. Is omega-3 good for your brain and the benefit of omega 3-6-9 take the yardstick further.

What do the trials show?

By outcome; doses are EPA plus DHA unless stated. Why is fish oil no longer recommended goes through those trials dose by dose.

• Triglycerides. In the Cochrane review of 86 trials and 162,796 people, long-chain omega-3 lowered triglycerides by about 15%, more at higher doses; the register wording applies at 2 g a day.^{2, 3} LDL does not fall, so "omega-3 lowers cholesterol" is the wrong sentence.
• Heart attacks, strokes and deaths. The same review found little or no effect on mortality or stroke and a small reduction in coronary heart disease events; in VITAL, 1 g of fish oil a day (840 mg of EPA and DHA) for a median 5.3 years did not reduce major cardiovascular events overall.^{3, 6, 14} Two trials at 4 g a day then disagreed: purified EPA cut events by a quarter in people with high triglycerides on statins, while EPA plus DHA against corn oil did nothing, for reasons still unsettled.^{7, 8}
• Atrial fibrillation. Across seven large trials, omega-3 raised the risk of new atrial fibrillation by about 25%: about 50% in trials above 1 g a day and about 12% at 1 g or less, from a starting rate of roughly 3 to 4% over five years.⁴ It is the signal behind "why is fish oil no longer recommended"; the UK never recommended fish oil capsules for everyone.²⁰
• Blood pressure. Down 2 to 3 mmHg systolic at 2 to 3 g a day in pooled trials; register wording at 3 g.⁹
• Brain, eyes and mood. Null for cognition in adults across 38 trials; null for dry eye at 3 g a day in the largest trial; null for macular degeneration progression in AREDS2.^{10, 11, 12} In diagnosed depression, adding an EPA-rich oil to usual care gave a small-to-moderate benefit and DHA-rich oils did not; in 18,353 adults aged 50 or over without depression, 1 g of fish oil a day for a median 5.3 years did not prevent it: new cases were slightly more frequent on omega-3 than on placebo (13.9 against 12.3 per 1,000 person-years) and mood scores did not differ.^{13, 14} Low mood is a reason to see a GP.
• Joints. In rheumatoid arthritis, pooled trials of three to four months found modest reductions in patient-reported pain, morning stiffness and painkiller use, and in the trials of 2.7 g or more a day for at least three months only the fall in painkiller use reached significance; the same is not established for osteoarthritis, where what is the best joint supplement ranks the evidence.^{15, 16}
• Pregnancy. In the Cochrane review of 70 trials, omega-3 reduced early preterm birth (before 34 weeks) from 4.6% to 2.7%; a later analysis found the benefit concentrated in women who started with low omega-3 levels.^{17, 18}
• Skin, hair and weight. Does omega 3-6-9 help with hair growth and does omega-3 make you bigger cover what has been studied, with the sources.

How much omega-3 do you need?

The NHS advice is at least two portions of fish a week, one oily, and it notes that most of us are not eating this much.¹⁹ SACN calculated that two portions, one white and one oily, supply about 450 mg of long-chain omega-3 a day, the UK population guideline: a food figure, with no supplement recommendation.²⁰ SACN's 2004 report put the population's average intake at about 0.1 g a day, which is the frame for deciding whether a supplement earns its place.²⁰ Read milligrams of EPA and DHA on the back, not milligrams of oil on the front: a standard 1,000 mg fish-oil capsule typically holds about 300 mg. EFSA concluded that supplemental EPA and DHA at up to 5 g a day raise no safety concerns for adults, far above any label.²¹ How much omega 3-6-9 do I need daily has the label-reading table; should omega-3 be taken daily explains why every trial dosed daily.

Omega-3, omega-6 and omega-9: what do the numbers mean?

Omega-6 means linoleic acid, the main polyunsaturated fat in sunflower, corn, soya and rapeseed oils, nuts and seeds, and the other essential fatty acid; its bad reputation is unearned: across 30 cohorts and 68,659 people, higher blood linoleic acid went with lower, not higher, cardiovascular disease and death.²² The "ideal omega-6 to omega-3 ratio" has no standing: EFSA sets separate intakes for each fat and no ratio, and every health claim built on a ratio was rejected on the GB register, so what matters is how much EPA and DHA you get, not how little omega-6.^{2, 27} Omega-9 means oleic acid, the monounsaturated fat of olive and rapeseed oil; the body makes it, so it is not essential, and the only register wording for it is that replacing saturated fat with unsaturated fat contributes to the maintenance of normal blood cholesterol. The dangers of omega-6 and the omega-9 explainer take each in turn.

A typical omega 3-6-9 is a flaxseed-oil capsule: a day's serving supplies several hundred milligrams of ALA against the 2 g a day at which the register's ALA cholesterol wording applies, with linoleic acid (omega-6) and oleic acid (omega-9) in flaxseed's own proportions and often vitamin E, which contributes to the protection of cells from oxidative stress; it contains no EPA or DHA, so it is a plant source of ALA alongside, not instead of, oily fish or algal oil. Is it better to take omega-3 or omega 3-6-9 works through that choice.

Where does omega-3 come from?

Figures are approximate EPA plus DHA per portion from the UK food composition tables (CoFID).²³

For ALA: a tablespoon of ground flaxseed has about 1.6 g, flaxseed oil about 7.5 g a tablespoon, 25 g of walnuts about 1.9 g, 25 g of chia about 4.5 g (USDA food tables). Algal oil is the direct route for anyone who will not eat fish: in a two-week comparison, 600 mg of DHA a day from algal-oil capsules raised blood DHA as much as the same amount from cooked salmon.²⁴ The NHS limits on shark, swordfish and marlin (none in pregnancy or under 16, otherwise no more than one portion a week) concern mercury in the fish itself.¹⁹ What foods are high in omega-3, 6 and 9 has the full food tables; algae omega-3 vs fish oil compares the sources and how to get enough omega-3 on a vegan diet the plant route.

Is omega-3 safe?

At label doses, yes, with four caveats. The common complaints are a fishy aftertaste, belching and loose stools; at 4 g a day in STRENGTH, gastrointestinal side effects affected 25% of people against 15% on corn oil.⁸ The atrial-fibrillation signal is dose-related, clear above 1 g a day and small at 1 g or less, so anyone with a heart rhythm condition should ask their cardiologist before exceeding a label dose.⁴ Bleeding is the fear that does not hold up: across 52 studies, including surgical patients, fish oil did not increase bleeding or transfusions and the authors saw no need to stop it before surgery; tell your surgeon anyway, and if you take warfarin or another anticoagulant tell your GP or anticoagulant clinic and keep the daily amount steady.²⁵ Vitamin A belongs to cod liver oil, not to omega-3: fish liver oils are high in retinol, which is why the NHS says to avoid them when pregnant or trying for a baby.¹⁹ Is there any danger when taking omega-3 covers anticoagulants, surgery and who should not take it; the side effects of omega 3-6-9 the everyday ones; the signs you need omega-3 why there is no reliable symptom of low intake.

What we don't know

• Why purified EPA and EPA plus DHA gave opposite results at 4 g a day: EPA-specific biology, the mineral-oil comparator or chance.^{7, 8}
• Whether 250 mg to 1 g a day changes hard outcomes in people who already eat oily fish: the supplement-dose trials were neutral on their primary outcomes.⁶
• How much ALA a given person converts: tracer studies range from almost none to a fifth.⁵

Frequently asked questions

Is omega-3 the same as fish oil?

No: fish oil is one carrier of EPA and DHA; algal oil carries DHA and sometimes EPA; flaxseed oil carries ALA, with no EPA or DHA.

Can you get enough omega-3 from food?

Yes, if you eat oily fish: SACN's 450 mg a day is what one oily and one white portion a week supply, against a population average of about 0.1 g a day.²⁰

Who should not take omega-3?

Anyone with a fish or shellfish allergy should avoid fish-derived oils; people with a heart rhythm condition should ask their cardiologist first; anyone on an anticoagulant should tell their GP or clinic; pregnant women should avoid fish liver oil for its vitamin A.¹⁹

Should I take omega-3 in the morning or at night?

Whichever comes with a meal: EPA and DHA are absorbed better with fat on the plate, and time of day has never been shown to matter; when to take omega-3, 6 and 9 has the absorption data.

Sources

1. Plourde M, Cunnane SC. Applied Physiology, Nutrition, and Metabolism, 2007. Review of ALA conversion in adults; publicly funded. PubMed 17622276.
2. Great Britain nutrition and health claims (NHC) register. Page last updated 19 May 2026. gov.uk.
3. Abdelhamid AS, et al. Omega-3 fatty acids for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews, 2020. 86 randomised trials, 162,796 people, 12 to 88 months; non-commercial funding. PubMed 32114706.
4. Gencer B, et al. Marine omega-3 supplementation and atrial fibrillation. Circulation, 2021. Meta-analysis, 7 trials, 81,210 people, 4.9 years; publicly funded. PubMed 34612056.
5. Burdge GC, Wootton SA. ALA conversion in young women. British Journal of Nutrition, 2002. Tracer study; funding not stated. PubMed 12323090.
6. Manson JE, et al. VITAL. New England Journal of Medicine, 2019. Randomised trial, 25,871 adults, 1 g fish oil a day, median 5.3 years; publicly funded. PubMed 30415637.
7. Bhatt DL, et al. REDUCE-IT. New England Journal of Medicine, 2019. Randomised trial, 8,179 statin-treated patients, 4 g icosapent ethyl a day, median 4.9 years; manufacturer-funded. PubMed 30415628.
8. Nicholls SJ, et al. STRENGTH. JAMA, 2020. Randomised trial, 13,078 statin-treated patients, 4 g a day vs corn oil, stopped early; manufacturer-funded. PubMed 33190147.
9. Zhang X, et al. Omega-3 intake and blood pressure: dose-response meta-analysis. Journal of the American Heart Association, 2022. 71 randomised trials, 4,973 people; funding not stated. PubMed 35647665.
10. Brainard JS, et al. Omega-3, omega-6 and polyunsaturated fat for cognition. Journal of the American Medical Directors Association, 2020. Meta-analysis, 38 randomised trials, 49,757 people; non-commercial funding. PubMed 32305302.
11. DREAM Study Research Group. New England Journal of Medicine, 2018. Randomised trial, 535 patients, 3 g a day, 12 months; publicly funded. PubMed 29652551.
12. AREDS2 Research Group. JAMA, 2013. Randomised trial, 4,203 people aged 50 to 85, median 5 years; publicly funded. PubMed 23644932.
13. Liao Y, et al. Omega-3 PUFAs in depression: meta-analysis. Translational Psychiatry, 2019. 26 randomised trials, 2,160 people; no conflicts declared. PubMed 31383846.
14. Okereke OI, et al. VITAL-DEP. JAMA, 2021. Randomised trial, 18,353 adults aged 50 or over, median 5.3 years; publicly funded. PubMed 34932079.
15. Goldberg RJ, Katz J. Omega-3 supplementation for inflammatory joint pain: meta-analysis. Pain, 2007. 17 randomised trials, 3 to 4 months; funding not stated. PubMed 17335973.
16. Lee YH, et al. Omega-3 and rheumatoid arthritis: meta-analysis. Archives of Medical Research, 2012. 10 randomised trials, 370 patients, 2.7 g or more a day; funding not stated. PubMed 22835600.
17. Middleton P, et al. Omega-3 fatty acid addition during pregnancy. Cochrane Database of Systematic Reviews, 2018. 70 randomised trials, 19,927 women; non-commercial funding. PubMed 30480773.
18. Simmonds LA, et al. Baseline omega-3 status and early preterm birth. BJOG, 2020. Exploratory analysis of the ORIP randomised trial; funding not stated. PubMed 32034969.
19. NHS. Fish and shellfish. Page last reviewed 26 June 2026. nhs.uk.
20. SACN. Advice on fish consumption: benefits and risks. Published 1 December 2004. gov.uk.
21. EFSA. EFSA assesses safety of long-chain omega-3 fatty acids. 27 July 2012. efsa.europa.eu.
22. Marklund M, et al. Biomarkers of dietary omega-6 and cardiovascular disease. Circulation, 2019. Pooled analysis, 30 cohorts, 68,659 people; publicly funded, two authors with food-industry support. PubMed 30971107.
23. Composition of foods integrated dataset (CoFID). Page last updated 19 March 2021. gov.uk.
24. Arterburn LM, et al. Algal-oil capsules and cooked salmon as sources of DHA. Journal of the American Dietetic Association, 2008. Randomised open-label trial, 32 adults, 2 weeks; industry-linked authors. PubMed 18589030.
25. Begtrup KM, et al. Fish oil supplements and bleeding risk: systematic review. Danish Medical Journal, 2017. 52 publications, 20 in surgical patients; funding not stated. PubMed 28552094.
26. Burdge GC, Jones AE, Wootton SA. ALA metabolism in young men. British Journal of Nutrition, 2002. Tracer study, 6 men; funding not stated. PubMed 12323085.
27. EFSA NDA Panel. Dietary reference values for fats. EFSA Journal, 2010 (restated in EFSA's 2017 DRV summary report). doi.org/10.2903/j.efsa.2010.1461.

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This article is general information, not medical advice. If you take an anticoagulant, have a heart rhythm condition, are pregnant or are planning surgery, speak to your GP, pharmacist or clinic before adding an omega-3 supplement.