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 about 5 to 10% 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

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 essential in the strict sense, because the body can lengthen ALA into EPA and DHA but cannot make ALA at all. The lengthening is the catch: most adults convert roughly 5 to 10% of ALA to EPA and under 1% to DHA; young women did better in one tracer study, about a fifth to EPA and 9% to DHA.^{1, 5} EPA and DHA, though often called essential, are not. 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, where DHA is the main omega-3 of the brain and retina; they are the raw material for signalling molecules, the eicosanoids made from EPA being less inflammatory than those from the omega-6 arachidonic acid; 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; improving memory, mood or joints belongs to the trials below. Is omega-3 good for your brain takes the 250 mg DHA figure further; the benefit of omega 3-6-9 applies the yardstick to a triple-omega capsule.

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, 840 mg a day for five years did not reduce major cardiovascular events overall.^{3, 6} 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, and nobody has settled why.^{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": supplement-dose heart trials were neutral, high-dose trials carry an atrial-fibrillation cost, and the UK never recommended fish oil capsules for everyone.
• 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 without depression, 1 g of fish oil a day did not lower the number of new cases.^{13, 14} Low mood is a reason to see a GP.
• Joints. In rheumatoid arthritis, 2.7 g or more a day for at least three months modestly reduced pain, morning stiffness and painkiller use; 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. No controlled trial has tested omega-3 alone for hair growth or skin hydration; does omega 3-6-9 help with hair growth and does omega-3 make you bigger cover what has been studied.

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, and that is the UK population guideline: a food figure, with no supplement recommendation for the general population.²⁰ Without oily fish the rest of the diet supplies only tens of milligrams of EPA and DHA a day, so the gap to 250 to 450 mg is real, which is the frame for deciding whether a supplement earns its place. Read milligrams of EPA and DHA on the back, not milligrams of oil on the front: a standard 1,000 mg fish-oil capsule is typically about 18% EPA and 12% DHA, so about 300 mg. The ceiling is high: 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 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.

The useful question about a 3-6-9 capsule is what it supplies in milligrams. A typical omega 3-6-9 is a flaxseed-oil capsule: a day's serving supplies several hundred milligrams of ALA, the essential omega-3, 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 sits in the UK intake picture as a plant source of ALA alongside, not instead of, the oily fish or algal oil that supply EPA and DHA. Is it better to take omega-3 or omega 3-6-9 works through that choice.

Where does omega-3 come from?

Oily fish first. Figures are EPA plus DHA per 140 g portion, from the per-100 g values SACN used.²⁰

For ALA: a tablespoon of ground flaxseed has about 1.6 g, flaxseed oil about 7 g a tablespoon, 25 g of walnuts about 2.3 g, 25 g of chia about 4.5 g. Algal oil is the direct route to EPA and DHA 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.²³ Algal DHA also comes in gummy form, at far lower doses per serving than an algal-oil capsule, so compare the label figure with the 250 mg of DHA at which the register's brain and vision wording applies; for a household that will not take fish, that is preformed DHA in a chewable form. Mercury binds to fish protein, not oil, so the NHS advice to avoid shark, swordfish and marlin is about eating those fish.¹⁹ What foods are high in omega-3, 6 and 9 has the full food tables. Algae omega-3 vs fish oil, cod liver oil and krill compares the sources, and how to get enough omega-3 on a vegan diet covers the plant route in full.

Is omega-3 safe?

At label doses, yes, with four things worth knowing. 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.²⁴ And 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; fish body oil, algal oil and flaxseed oil contain none.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. What are the signs you need omega-3 explains 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, about 30% of a standard capsule by weight; 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; without oily fish, EPA and DHA come only in tens of milligrams.²⁰

What happens if you take omega-3 every day?

Blood EPA and DHA rise over four to twelve weeks and plateau, triglycerides fall a little with dose, nothing happens that you would feel, and the trials dosed daily for years.³

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.

Is omega-3 or omega-6 anti-inflammatory?

Neither label fits: EPA and DHA give rise to the resolvins that switch inflammation off, while linoleic acid tracks lower, not higher, cardiovascular risk, so the answer is enough omega-3 rather than less omega-6.²²

Do vegans need omega-3?

Everyone needs ALA, which a vegan diet supplies easily; EPA and DHA are the question, and since algal DHA raises blood DHA as effectively as fish DHA, the vegan answer is ALA from food plus an algal source, read in milligrams.^{1, 23}

Sources

1. Plourde M, Cunnane SC. Extremely limited synthesis of long chain polyunsaturates in adults. 2007. PubMed 17622276.
2. Great Britain nutrition and health claims (NHC) register. gov.uk.
3. Abdelhamid AS. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane, 2020. PubMed 32114706.
4. Gencer B. Marine omega-3 supplementation and the risk of atrial fibrillation: meta-analysis of cardiovascular outcome trials. 2021. PubMed 34612056.
5. Burdge GC, Wootton SA. Conversion of alpha-linolenic acid to EPA, DPA and DHA in young women. 2002. PubMed 12323090.
6. Manson JE. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer (VITAL). 2019. PubMed 30415637.
7. Bhatt DL. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia (REDUCE-IT). 2019. PubMed 30415628.
8. Nicholls SJ. High-dose omega-3 fatty acids vs corn oil and major adverse cardiovascular events (STRENGTH). 2020. PubMed 33190147.
9. Zhang X. Omega-3 polyunsaturated fatty acids intake and blood pressure: a dose-response meta-analysis. 2022. PubMed 35647665.
10. Brainard JS. Omega-3, omega-6 and polyunsaturated fat for cognition: meta-analysis of randomised trials. 2020. PubMed 32305302.
11. DREAM Study Research Group. n-3 fatty acid supplementation for the treatment of dry eye disease. 2018. PubMed 29652551.
12. AREDS2 Research Group. Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration. 2013. PubMed 23644932.
13. Liao Y. Efficacy of omega-3 PUFAs in depression: a meta-analysis. 2019. PubMed 31383846.
14. Okereke OI. Marine omega-3 fatty acids vs placebo and risk of depression (VITAL-DEP). 2021. PubMed 34932079.
15. Goldberg RJ, Katz J. A meta-analysis of the analgesic effects of omega-3 supplementation for inflammatory joint pain. 2007. PubMed 17335973.
16. Lee YH. Omega-3 polyunsaturated fatty acids and the treatment of rheumatoid arthritis: a meta-analysis. 2012. PubMed 22835600.
17. Middleton P. Omega-3 fatty acid addition during pregnancy. Cochrane, 2018. PubMed 30480773.
18. Simmonds LA. Omega-3 fatty acid supplementation in pregnancy: baseline omega-3 status and early preterm birth. 2020. PubMed 32034969.
19. NHS. Fish and shellfish. nhs.uk.
20. SACN. Advice on fish consumption: benefits and risks, 2004 (Table 4.2). gov.uk.
21. EFSA. EFSA assesses safety of long-chain omega-3 fatty acids, 2012. efsa.europa.eu.
22. Marklund M. Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality: pooled analysis of 30 cohorts. 2019. PubMed 30971107.
23. Arterburn LM. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. 2008. PubMed 18589030.
24. Begtrup KM, Krag AE, Hvas AM. No impact of fish oil supplements on bleeding risk: a systematic review. 2017. PubMed 28552094.

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.