Supplements › Fatty acid or lipid

Omega-3 fatty acids

Fats the body needs from food: ALA from plants, EPA and [DHA](/supplements/docosahexaenoic-acid) from fish and algae. Most studied for triglycerides, the heart and pregnancy.

Strongest evidenceHeart healthStrong, 423 studies
Median dose in studies2,000 mg a dayFrom 1,387 study groups
Adequate intake of ALA1.6 g a day for men1.1 g for women. US, adults. No US intake is set for EPA or DHA.
Upper limitNone setEFSA and the US FDA consider up to 5 g of EPA and DHA a day safe for adults.
Ask a doctor or pharmacist first

Ask a doctor or pharmacist first if you:

  • take warfarin or a similar blood thinner: fish oil may prolong clotting times, and labels of prescription omega-3 call for checks of INR, a clotting test[1]
  • have heart disease or a high risk of it: in two large trials, 4 g a day for several years slightly raised atrial fibrillation, an irregular heartbeat[1]
  • want to take cod liver oil: it also contains vitamins A and D, which can be harmful in large amounts[2]
  • are pregnant and eat a vegetarian or vegan diet: advice listed by the NIH is to ask a health care provider whether EPA and DHA supplements are needed[1]
  • have rheumatoid arthritis: do not change prescribed medicines because you take omega-3[2]
  • have depression: talk to a health care provider before you take omega-3 for it[2]

Overview

What are omega-3 fatty acids?

Omega-3 fatty acids are a family of fats that the body uses to build cell membranes. Research focuses on three of them: ALA from plant oils, and EPA and DHA from fish.[1] The body cannot make ALA, and it turns less than 15% of ALA into EPA and DHA.[1]

ALA is in flaxseed, soybean and canola oils, chia seeds and walnuts. EPA and DHA are in fatty fish such as salmon, mackerel, herring and sardines.[1] Fish do not make them: microalgae do, and fish collect them through the food chain.[1] Supplements include fish oil, krill oil, cod liver oil, algae oil and flaxseed oil.[2]

What are omega-3 fatty acids used for?

Most research tested EPA and DHA from fish or supplements, not ALA from plants.[1] The clearest effects in reviews are triglycerides about 15% lower and fewer preterm births when taken in pregnancy.[3][4] Effects on heart disease and blood pressure are small.[3][5] Reviews found little or no effect on dementia or cognitive decline, ADHD symptoms or body weight.[6][7][8] A large trial found no benefit for dry eyes.[9]

Are omega-3 supplements safe?

Side effects are usually mild: an unpleasant taste, bad breath, heartburn, nausea, stomach upset, diarrhea, headache and smelly sweat.[1][2] EFSA and the US FDA consider up to 5 g of EPA and DHA a day safe for adults.[10][1]

Two large trials gave 4 g a day for several years to people with heart disease or at high risk of it. They found slightly more atrial fibrillation, an irregular heartbeat.[1] Fish oil may prolong clotting times in people who take warfarin, and labels of prescription omega-3 advise regular checks of INR, a clotting test, with blood thinners.[1] Cod liver oil also contains vitamins A and D, which can be harmful in large amounts.[2] Omega-3 supplements have not been found to contain mercury, because processing removes it.[1]

How it works

Omega-3 fatty acids are a family of fats. Research focuses on three of them: ALA, EPA and DHA.[1] The body cannot make ALA, so it has to come from food.[1]

  1. Gut absorption

    The gut splits omega-3 fats like other fats and absorbs about 95% of them.[1] Gut cells pack them into chylomicrons, particles that reach the blood through the lymph.[1]

  2. ALA conversion

    The liver turns a small part of ALA into EPA and then into DHA, at reported rates below 15%.[1] Extra ALA raises EPA in the blood but changes DHA very little.[11]

  3. Cell membranes

    EPA and DHA become part of the membranes of cells. DHA is especially high in the retina, the brain and sperm.[1]

  4. Signal molecules

    Cells make signal molecules called eicosanoids from omega-3 and omega-6 fats. Those made from omega-6 fats generally drive inflammation more, and more EPA and DHA moves the balance toward less inflammatory activity.[1]

  5. Omega-3 index

    The share of EPA and DHA in red blood cell membranes reflects intake over about the last 120 days. In Western countries where people eat little fish, it is about 3% to 5%.[1]

Benefits and studies

Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.

StrongModerateWeakNo trials
BenefitMain effects in studiesStudiesPeople

Dose

Large heart trials gave 1 g of omega-3 a day, or 4 g a day of a prescription form.[1] The US has set an adequate intake only for ALA: 1.6 g a day for men and 1.1 g for women.[1] EFSA, the EU food safety authority, gives 250 to 500 mg of EPA and DHA a day as the dietary recommendation for European adults.[10]

Usual dose

VITAL and ASCEND gave 1 g a day, with 460 mg of EPA and 380 mg of DHA. REDUCE-IT and STRENGTH gave 4 g a day of prescription omega-3.[1] For blood pressure, a review of 71 trials found the largest fall at 2 to 3 g of EPA and DHA a day.[5] In 11 trials of algae oil, the median dose was 1.68 g of DHA a day.[12]

Daily need

The US adequate intake covers ALA only: from age 14 it is 1.6 g a day for men and 1.1 g for women, 1.4 g in pregnancy and 1.3 g when breastfeeding.[1] The US has set no intake for EPA or DHA.[1] EFSA advises 100 to 200 mg of DHA a day on top of the adult amount in pregnancy.[1]

Form

ALA comes from flaxseed, soybean and canola oils, chia seeds and walnuts.[1] EPA and DHA come as fish oil, krill oil, cod liver oil and algae oil.[1] Algae oil products usually provide about 100 to 300 mg of DHA, and some also contain EPA.[1]

How long

In a 2-week trial, 600 mg of DHA a day raised DHA by about 80% in plasma and by about 25% in red blood cells.[13] The red blood cell level reflects about 120 days of intake.[1]

Upper limit

Neither the US nor the EU has set an upper limit.[1][10] EFSA found no safety concern for adults at up to 5 g of EPA and DHA a day, and the US FDA also considers 5 g a day safe.[10][1] US supplement labels should not recommend more than 2 g a day.[1] People who take medicines every day should ask a doctor or pharmacist about interactions first.[1]

Doses in studies

Most studies gave 1,000 to 2,500 mg a day, for 1 to 3 months.

The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.

How much a day1,387 groups in 1,018 studies
  1. Up to 100 mg22 groups
  2. 100 to 250 mg52 groups
  3. 250 to 500 mg85 groups
  4. 500 to 1,000 mg268 groups
  5. 1,000 to 2,500 mg494 groups
  6. 2,500 to 5,000 mg408 groups
  7. 5,000 mg or more58 groups
For how long1,327 groups in 969 studies
  1. 1 week or less63 groups
  2. 1 to 4 weeks127 groups
  3. 1 to 3 months691 groups
  4. 3 to 6 months232 groups
  5. 6 to 12 months112 groups
  6. More than a year102 groups
Half of the groups took less than 2,000 mg a day. Half took more.Half of the groups took 1,000 to 3,157 mg a day. A quarter took less, a quarter took more.1228 of 1387 groups took 500 mg a day or more. Do not copy a study dose without a doctor.

Taken together

516 of 1400 study groups took omega-3 fatty acids with something else. This shows what studies gave together, not what works together.

  1. Docosahexaenoic Acid191 studies244
  2. Fish Oil103 studies124
  3. Vitamin E53 studies57
  4. Vitamin D35 studies37
  5. Vitamin C15 studies17
  6. EPA12 studies15
  7. Lutein12 studies13
  8. Phytosterols8 studies12
  9. Selenium8 studies12
  10. Vitamin A10 studies12
Bars and numbers count study groups. A companion is shown only when at least 3 different studies gave it.

Protocols

What studies used when they gave omega-3 fatty acids for one goal, or to a group of people.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Questions

12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.

Basics
What is the difference between ALA, EPA and DHA?

ALA is a shorter omega-3 fat with 18 carbon atoms. It comes from plant oils such as flaxseed, soybean and canola.[1] EPA, with 20 carbon atoms, and DHA, with 22, are long-chain omega-3 fats from fish, fish oil, krill oil and algae.[1] The body needs ALA from food and turns less than 15% of it into EPA and DHA.[1]

Read the full answer ›
Which foods are high in omega-3?

For ALA: flaxseed oil (7.26 g per tablespoon), chia seeds (5.06 g per 28 g), English walnuts (2.57 g per 28 g) and canola oil (1.28 g per tablespoon).[1] For EPA and DHA: fatty fish such as salmon, herring, sardines and mackerel. A cooked 85 g serving of farmed Atlantic salmon has 1.24 g of DHA and 0.59 g of EPA.[1]

Leaner fish such as cod and tilapia, and shellfish, have less.[1] Some brands of eggs, milk, yogurt and soy drinks have added DHA.[1] US dietary guidelines advise adults to eat at least 8 ounces (about 230 g) of a variety of seafood a week.[2]

Open the answer with sources ›
Benefits
Does plant omega-3 (ALA) protect the heart?

Possibly a little. A 2020 Cochrane review of 5 trials with 19,327 people found that more ALA may slightly reduce cardiovascular events and probably slightly reduces arrhythmia. It made little or no difference to deaths.[3] Studies that observe people link more ALA in the diet with about a 10% lower risk of cardiovascular disease.[14]

Read the full answer ›
Does omega-3 lower blood pressure?

A little. A 2022 review pooled 71 trials with 4,973 adults.[5] At 2 to 3 g of EPA and DHA a day, systolic blood pressure fell by about 2.6 mmHg and diastolic by about 1.6 to 1.8 mmHg.[5] The fall was larger in people with high blood pressure or high blood fats, and in older people.[5] The 2020 Cochrane review found little or no effect on blood pressure.[3]

For plant omega-3, one trial gave 30 g of milled flaxseed a day for 6 months to people with peripheral artery disease. Systolic pressure was about 10 mmHg lower than with placebo.[15] The trials in the 2022 review gave a median of 2.8 g of EPA and DHA a day (omega-3 for blood pressure).[5]

Open the answer with sources ›
Does omega-3 help dry eyes?

A large trial found no benefit. In the DREAM trial, 535 people with moderate to severe dry eye took 3000 mg of EPA and DHA a day or an olive oil placebo for 12 months. Symptoms improved about the same in both groups.[9] In an add-on study of the VITAL trial, 1 g a day for a median of 5.3 years did not prevent dry eye in 23,523 adults.[1]

A 2026 review of 27 trials found no consistent benefit across the causes of dry eye.[16] It found benefits in dry eye linked to screen use or contact lenses, but none in dry eye from meibomian gland problems, the oil glands of the eyelids.[16]

Open the answer with sources ›
Does omega-3 help children with ADHD?

Probably not for the main symptoms. A 2023 Cochrane review of 37 trials with more than 2,374 children and teenagers found high-certainty evidence that omega-3 and omega-6 supplements did not change parent-rated ADHD symptoms, inattention or hyperactivity.[7] Supplements were given for 2 weeks to 6 months.[7]

A smaller analysis of 3 trials, with low certainty, found that more children improved with the supplements than with placebo.[7] Side effects did not differ from placebo.[7]

Open the answer with sources ›
Does omega-3 help muscles recover after exercise?

It may reduce muscle soreness after hard exercise. A 2026 review pooled 9 placebo-controlled trials of eccentric exercise, in which muscles work while they lengthen. EPA and DHA reduced delayed muscle soreness, creatine kinase (a marker of muscle damage) and muscle swelling, and strength came back better.[17]

Across all 43 studies in the review, the authors called the effect equivocal, with many problems in study design. They could not say which dose works and called for studies that test doses.[17]

Open the answer with sources ›
Does DHA in pregnancy improve brain development in children?

Trials have not shown it. A 2026 review pooled 19 trials and found no benefit of DHA in pregnancy on children's attention, motor skills, intelligence, language, executive function or short-term memory.[18] Birth weight was about 73 g higher.[18] A 2018 Cochrane review also found very few differences in children's cognition, IQ, vision or behaviour.[4]

In the DOMInO trial, 2,399 women took 800 mg of DHA a day or a vegetable oil from before 21 weeks of pregnancy until birth. Their children's cognitive and language scores at 18 months did not differ.[19] Omega-3 in pregnancy did lower the risk of preterm birth by 11% and of early preterm birth by 42%.[4]

Open the answer with sources ›
Safety
How much omega-3 is too much?

No upper limit has been set in the US or the EU.[1][10] EFSA found no safety concern for adults at up to 5 g of EPA and DHA a day, or 1.8 g of EPA alone. For the general population, about 1 g of DHA alone a day raises no concern.[10] At 2 to 6 g of EPA and DHA a day, LDL cholesterol rose by about 3%.[10]

US experts noted that 2 to 15 g a day might lengthen bleeding time.[1] In two large trials, 4 g a day for several years slightly raised atrial fibrillation in people with heart disease or at high risk of it.[1] US supplement labels should not recommend more than 2 g a day.[1]

Open the answer with sources ›
Forms and timing
Is algae oil as good as fish oil?

For raising blood DHA, studies suggest so. In a 2-week trial in 32 adults, 600 mg of DHA a day from algae oil capsules raised blood DHA as much as the same amount from cooked salmon.[13] A 2012 review of 11 trials found that DHA from algae oil lowered triglycerides.[12] Most algae oils give mainly DHA, about 100 to 300 mg, and only some add EPA.[1]

Read the full answer ›
Can flaxseed oil replace fish oil?

Not as a source of EPA and DHA. Flaxseed oil provides ALA, 7.26 g per tablespoon, not EPA or DHA.[1] The body turns less than 15% of ALA into EPA and DHA.[1] Extra ALA raises EPA but has little effect on blood DHA.[11]

In a 2022 review of 13 trials, high doses of flaxseed oil did not raise the omega-3 index, while algae oil did.[20] ALA has its own small benefits: in a 2020 Cochrane review, more ALA probably slightly reduced arrhythmia.[3] Algae oil is a vegetarian source of DHA, and in one trial it raised blood DHA as much as cooked salmon.[2][13]

Open the answer with sources ›
Which is better, EPA or DHA?

It depends on the effect studied. In a 2011 review, both lowered triglycerides, and DHA lowered them more in direct comparisons. DHA raised LDL cholesterol by about 7 mg/dL compared with placebo, while EPA did not.[21] For depression, a 2019 review found benefit with products that were at least 60% EPA, at up to 1 g of EPA a day.[22] Products that were mainly DHA showed no such benefit.[22]

A 2026 review of 96 trials found that products with more DHA than EPA lowered inflammatory signal molecules the most.[23] DHA builds up in the brain and retina fastest in late pregnancy, and in the brain until age 2.[1] Fish oil contains both: a typical 1000 mg capsule has 180 mg of EPA and 120 mg of DHA.[1]

Open the answer with sources ›

References

  1. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  2. Omega-3 Supplements: What You Need To Know. NIH National Center for Complementary and Integrative Health, 2024. www.nccih.nih.gov
  3. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, et al. Cochrane Database Syst Rev, 2020. PMID 32114706
  4. Omega-3 fatty acid addition during pregnancy. Middleton P, Gomersall JC, Gould JF, Shepherd E, Olsen SF, Makrides M Cochrane Database Syst Rev, 2018. PMID 30480773
  5. Omega-3 Polyunsaturated Fatty Acids Intake and Blood Pressure: A Dose-Response Meta-Analysis of Randomized Controlled Trials. Zhang X, Ritonja JA, Zhou N, Chen BE, Li X J Am Heart Assoc, 2022. PMID 35647665
  6. Omega-3, Omega-6, and Polyunsaturated Fat for Cognition: Systematic Review and Meta-analysis of Randomized Trials. Brainard JS, Jimoh OF, Deane KHO, Biswas P, Donaldson D, Maas K, et al. J Am Med Dir Assoc, 2020. PMID 32305302

Review history

  1. 9 Nov 2026CheckedReviewerChecked every claim against its source.
  2. 9 Nov 2026Page createdResearcherFirst edition, written from PubMed and public health sources.