Omega-3 fatty acids are essential fats that your body needs for the structure of every cell membrane. The three main ones are ALA from plants and EPA and DHA from seafood and algae. DHA is especially concentrated in the brain and the retina of the eye. Large trials of omega-3 supplements have produced mixed results, so the amount you get, its source and the form matter more than broad promises on a label.
Key Takeaways
- ALA is the only omega-3 with an official U.S. intake value: an Adequate Intake of 1.6 g a day for men and 1.1 g a day for women.
- The body converts less than 15% of ALA into EPA and DHA, so seafood, fish oil, krill oil or algal oil are the practical ways to raise EPA and DHA levels.
- DHA is a building block of cell membranes in the brain and retina, and it builds up fastest in a baby's brain during the third trimester and the first two years after birth.
- Large randomized trials of omega-3 supplements have had mixed results, and results at about 1 g a day differ from those at 4 g a day of prescription products.
- Judge any product by the EPA and DHA on the Supplement Facts panel, not the total fish oil.
- Talk to your doctor before taking omega-3 supplements if you take warfarin or another blood-thinning medicine; trials of higher doses also found more irregular heart rhythm.
Evidence grade: Strong. NIH has set Adequate Intakes for ALA and documents the structural roles of EPA and DHA, and omega-3 supplements have been tested in several large randomized trials and Cochrane-level reviews, although results for specific health outcomes are mixed.
ALA, EPA and DHA: The Three Main Omega-3s
Omega-3s are polyunsaturated fats. Their name comes from the position of the first double bond, three carbons from the end of the fatty acid chain. The NIH Office of Dietary Supplements (ODS) explains that most research focuses on three of them:
- ALA (alpha-linolenic acid) has 18 carbons. It is found in plant oils such as flaxseed, soybean and canola oil, and in chia seeds and walnuts. Your body cannot make ALA, so it is an essential fatty acid that must come from food.
- EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are long-chain omega-3s. They are found in fish, fish oil and krill oil. Fish do not make them; microalgae at the base of the marine food chain do, and fish accumulate them as they eat.
How much ALA becomes EPA and DHA?
Not much. ALA can be converted into EPA and then into DHA, mainly in the liver, but ODS reports that conversion rates are very limited, below 15%. Because of that, ODS says eating EPA and DHA directly, from foods or supplements, is the only practical way to raise their levels in the body. For people who eat no fish or seafood, algal oil is the vegetarian supplement source of DHA. For more on plant-based diets, see our guide to essential nutrients that can be missing in vegan diets.
What Omega-3s Do in the Body
According to ODS, omega-3s are components of the phospholipids that form cell membranes. DHA is especially high in the retina, the brain and sperm cells. Besides their structural role, omega-3s supply energy, and they are used to make eicosanoids, signaling molecules involved in the cardiovascular, pulmonary, immune and endocrine systems.
Brain and eyes
DHA's concentration in the brain and retina is the main reason omega-3s are linked with brain and eye development. ODS notes that DHA accumulates most rapidly during the third trimester of pregnancy. Its build-up in the retina is complete by birth, while build-up in the brain continues for the first two years of life. Human milk contains ALA, EPA and DHA, and since 2002 most infant formulas in the U.S. have added DHA and arachidonic acid, the two most common long-chain polyunsaturated fats in the brain.
A true omega-3 deficiency is very rare in the United States, according to ODS. Most people get enough ALA from food, along with small amounts of EPA and DHA. For how omega-3s fit with other fats in an overall eating pattern, see our overview of dietary fats.
How Much Omega-3 Do You Need?
The Institute of Medicine (now the National Academy of Medicine) set Adequate Intakes (AIs) for omega-3s. For infants the AI covers total omega-3s. From age 1 on, it applies only to ALA, because ALA is the only omega-3 that is essential. No official U.S. intake value has been set for EPA or DHA.
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| Birth to 12 months (total omega-3s) | 0.5 g | 0.5 g | ||
| 1-3 years (ALA) | 0.7 g | 0.7 g | ||
| 4-8 years (ALA) | 0.9 g | 0.9 g | ||
| 9-13 years (ALA) | 1.2 g | 1.0 g | ||
| 14-18 years (ALA) | 1.6 g | 1.1 g | 1.4 g | 1.3 g |
| 19 years and older (ALA) | 1.6 g | 1.1 g | 1.4 g | 1.3 g |
For EPA and DHA, U.S. guidance is food-based. The Dietary Guidelines for Americans recommend that adults eat 8 ounces or more of a variety of seafood a week, including some choices higher in EPA and DHA. How many milligrams a typical capsule supplies, and how much is too much, is covered in detail in our guide Is 1000 mg of fish oil too much?
Food Sources of Omega-3s
The omega-3 content of fish varies widely. ODS lists cold-water fatty fish such as salmon, mackerel, herring, sardines and tuna as high in EPA and DHA, while leaner fish such as tilapia and cod, and most shellfish, contain less. Farmed fish often have more EPA and DHA than wild fish, but it depends on their feed. The table below uses ODS figures (grams per serving) and the mercury categories from the FDA and EPA's Advice about Eating Fish.
| Food | ALA (g) | DHA (g) | EPA (g) | FDA/EPA mercury category |
|---|---|---|---|---|
| Salmon, Atlantic, farmed, cooked, 3 oz | 1.24 | 0.59 | Best choice | |
| Salmon, Atlantic, wild, cooked, 3 oz | 1.22 | 0.35 | Best choice | |
| Herring, Atlantic, cooked, 3 oz | 0.94 | 0.77 | Best choice | |
| Sardines, canned in tomato sauce, 3 oz | 0.74 | 0.45 | Best choice | |
| Mackerel, Atlantic, cooked, 3 oz | 0.59 | 0.43 | Best choice | |
| Trout, rainbow, wild, cooked, 3 oz | 0.44 | 0.40 | Best choice (freshwater trout) | |
| Tuna, light, canned in water, 3 oz | 0.17 | 0.02 | Best choice | |
| Shrimp, cooked, 3 oz | 0.12 | 0.12 | Best choice | |
| Flaxseed oil, 1 tbsp | 7.26 | Not applicable | ||
| Chia seeds, 1 oz | 5.06 | Not applicable | ||
| English walnuts, 1 oz | 2.57 | Not applicable | ||
| Flaxseed, whole, 1 tbsp | 2.35 | Not applicable | ||
| Canola oil, 1 tbsp | 1.28 | Not applicable |
Choosing fish that are lower in mercury
Seafood contains varying levels of methylmercury, which can harm the developing brain and nervous system in large amounts. The FDA and EPA advice is written for people who are or might become pregnant, those who are breastfeeding, and parents feeding children ages 1 to 11. It recommends 8 to 12 ounces of a variety of fish a week during pregnancy and breastfeeding, which is 2 to 3 servings a week from the "Best Choices" list. Salmon, sardines, herring, Atlantic mackerel, anchovies, trout, cod, shrimp and canned light tuna are all on that list. The fish to avoid, because they have the highest mercury levels, are king mackerel, marlin, orange roughy, shark, swordfish, tilefish from the Gulf of Mexico and bigeye tuna. ODS notes that omega-3 supplements have not been found to contain methylmercury, because it is removed during processing.
Omega-3 Supplement Forms
ODS describes several types of omega-3 supplements: fish oil, krill oil, cod liver oil and algal oil. The form of the omega-3 inside also varies.
| Form | What it is | What ODS says about absorption |
|---|---|---|
| Fish oil, natural triglyceride | The form that occurs naturally in fish oil | Somewhat higher bioavailability than ethyl esters |
| Fish oil, ethyl ester | Made from natural triglycerides by replacing glycerol with ethanol; often used in concentrates | Somewhat lower than other forms, but still significantly raises blood EPA and DHA |
| Re-esterified triglyceride | Ethyl esters converted back into triglycerides | Somewhat higher than ethyl esters |
| Krill oil | Omega-3s mainly as phospholipids | Some studies suggest higher bioavailability than fish oil; others do not |
| Algal oil | Vegetarian source; usually 100-300 mg DHA, sometimes with EPA, typically as triglycerides | A small study found DHA bioavailability equivalent to cooked salmon |
| Cod liver oil | Fish liver oil with EPA and DHA | Also supplies vitamins A and D, which count toward your totals |
All of these forms significantly raise blood EPA and DHA, so the amount on the label usually matters more than the form.
How to Read EPA and DHA on a Label
A fish oil label often shows a large number, such as 1,000 mg, which is the weight of the oil. ODS says a typical 1,000 mg fish oil supplement provides about 180 mg EPA and 120 mg DHA, but amounts vary widely. To compare products:
- Find the separate EPA and DHA lines on the Supplement Facts panel and add them together.
- Check the serving size. If one serving is two capsules or two gummies, the amounts are for both.
- Count every product you take that contains omega-3s, including multivitamins and cod liver oil.
- Note that the FDA says supplement labels should not recommend more than 2 g of EPA and DHA a day.
Our own OPA Omega 3 Gummies are a good example of why this matters. A two-gummy serving lists 100 mg of fish oil powder providing 13.2 mg DHA and 2.8 mg EPA, or 16 mg of EPA plus DHA. That is far below the amounts used in the trials described below, such as 840 mg a day in VITAL and 4 g a day in REDUCE-IT and STRENGTH. The gummies are a chewable orange-flavored format for adults who want a small daily omega-3 amount. They contain tuna fish and 2.8 g of added sugar per serving.
The Omega-3 Index
ODS notes that most clinicians do not test omega-3 status, but it can be measured. Plasma and serum levels vary with your most recent meal, so they do not reflect long-term intake, while red blood cell fatty acids reflect intake over roughly the previous 120 days. The omega-3 index, proposed by researchers William Harris and Clemens von Schacky, is the EPA plus DHA in red blood cell membranes as a percentage of total red blood cell fatty acids. ODS describes it as a surrogate for tissue levels of EPA and DHA. In Western populations with low fish intake, EPA and DHA typically make up about 3% to 5% of red blood cell fatty acids. In Japan, where people eat much more fish, levels are about twice as high. ODS also notes that experts have not established normal ranges for plasma omega-3 levels.
What the Large Trials Found
Observational studies link eating more fish with better health outcomes, but they cannot show cause and effect. The randomized trials below are reported as research, not recommendations.
VITAL (2019): 1 g a day in the general population
VITAL enrolled 25,871 U.S. men aged 50 and older and women aged 55 and older. Participants took 1 g a day of marine omega-3s (460 mg EPA and 380 mg DHA) or a placebo for a median of 5.3 years. The supplement did not significantly change the main combined outcome of major cardiovascular events (hazard ratio 0.92, not statistically significant). Among secondary outcomes, the omega-3 group had fewer total heart attacks (hazard ratio 0.72), with no significant difference in strokes or in deaths from cardiovascular causes.
REDUCE-IT (2019): 4 g a day of a prescription EPA product
REDUCE-IT tested a high-dose prescription form of purified EPA (icosapent ethyl, an ethyl ester), not an over-the-counter supplement. Its 8,179 participants already had cardiovascular disease, or had diabetes plus other risk factors, and had elevated triglycerides despite their usual medical care. Over a median of 4.9 years, the main combined outcome occurred in 17.2% of the EPA group and 22.0% of the placebo group. Hospitalization for atrial fibrillation or flutter was more common with EPA (3.1% vs 2.1%). The placebo was mineral oil, and ODS notes it is not a neutral placebo, which may have made the difference between groups look larger.
STRENGTH (2020): 4 g a day of a prescription EPA plus DHA product
STRENGTH gave 13,078 adults at high cardiovascular risk 4 g a day of a prescription EPA and DHA product (in carboxylic acid form) or corn oil. The trial was stopped early because benefit looked unlikely. The main outcome occurred in 12.0% of the omega-3 group and 12.2% of the corn oil group. Gastrointestinal side effects were more common with omega-3 (24.7% vs 14.7%), and ODS notes the omega-3 group had more atrial fibrillation. ODS says the reasons the two 4 g trials differed are unclear and may include formulation, populations and placebo oils. The National Center for Complementary and Integrative Health (NCCIH) adds that prescription products may not have the same effects as dietary supplements.
Cognitive function trials
ODS reports that some, but not all, observational studies link diets high in EPA and DHA with less cognitive decline. Trials of supplements have been less encouraging. In the OPAL trial, 867 cognitively healthy adults aged 70 to 79 in England and Wales took 200 mg EPA plus 500 mg DHA or olive oil daily for 24 months. Among the 748 who finished, scores did not differ between groups; neither group declined, which the authors said may have limited the trial's ability to detect an effect. Summing up the systematic reviews, ODS concludes that omega-3 supplements do not appear to affect cognitive function in healthy older adults. NCCIH notes that a 2022 review of 33 studies suggested omega-3s from food and supplements may have a protective effect against cognitive decline in healthy people, so the question is still open. For other nutrients studied for brain function, see nutrition and brain health.
Mood and attention research
Omega-3s have also been studied for mood and attention. NCCIH summarizes this research as uncertain. A 2021 review of 35 studies (1,964 participants) concluded that if omega-3 supplements have an effect on depressive symptoms, it may be too small to be meaningful, and the quality of the evidence was low or very low. Research on ADHD has had conflicting results. If you have concerns about your mood or attention, talk with a healthcare provider; a supplement is not a substitute for professional care.
Pregnancy, DHA and infant development
Fish intake during pregnancy is recommended by the FDA and EPA, which state that moderate scientific evidence shows it can help a baby's cognitive development. ODS describes a systematic review of 29 cohort studies in 102,944 mother-child pairs, in which maternal seafood intake of 4 ounces a week was associated with better neurocognitive development in children.
Supplement trials are less clear. In the DOMInO trial, 2,399 Australian women took DHA-rich fish oil (800 mg DHA a day) or vegetable oil capsules from mid-pregnancy to birth. At 18 months, children's cognitive and language scores did not differ between groups. ODS says randomized trials have not shown consistent benefits of prenatal EPA or DHA supplements on infant cognition or visual development. A 2018 Cochrane review of 70 trials in 19,927 women found that omega-3s during pregnancy were associated with fewer births before 37 weeks and before 34 weeks and fewer low-birthweight babies, with a probable increase in pregnancies lasting beyond 42 weeks. If you are pregnant, ask your obstetrician or midwife whether a supplement makes sense for you. Our guide to key nutrients for fetal development covers the wider picture.
Safety and Interactions
Common side effects
ODS and NCCIH describe the side effects of omega-3 supplements as usually mild: unpleasant taste, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache and bad-smelling sweat.
How much is considered safe
No Tolerable Upper Intake Level has been set for omega-3s. In 2019 the FDA concluded that dietary supplements providing no more than 5 g a day of EPA and DHA are safe when used as labeled, and that there is not enough evidence to draw a conclusion above 5 g a day, mainly about bleeding. ODS reports that the European Food Safety Authority reached a similar view for long-term intakes up to about 5 g a day. For the full dose breakdown, see our fish oil dose and safety guide.
Atrial fibrillation at higher doses
Atrial fibrillation is a type of irregular heart rhythm. A 2021 meta-analysis of seven large randomized trials (81,210 participants, average age 65) found that omega-3 supplements were associated with a 25% higher risk of atrial fibrillation overall. The increase was larger in trials testing more than 1 g a day (hazard ratio 1.49) than in trials testing 1 g a day or less (hazard ratio 1.12). ODS notes that two large trials of 4 g a day for several years found a slightly higher risk in people with, or at high risk of, cardiovascular disease. If you have a heart rhythm condition, talk to your doctor before taking omega-3 supplements.
Bleeding and medicines
Fish oil can have antiplatelet effects at high doses, although ODS says it appears less potent than aspirin. The Institute of Medicine noted that 2 to 15 g a day of EPA and/or DHA might increase bleeding time. Fish oil might raise the INR (a measure of clotting time) when taken with warfarin, although most research shows 3 to 6 g a day of fish oil does not significantly change clotting status in people taking warfarin. Talk to your doctor or pharmacist before taking omega-3 supplements if you take warfarin (Coumadin) or another anticoagulant or antiplatelet medicine.
Other cautions
Cod liver oil also provides vitamins A and D, which can be harmful in excess, so count them toward your totals. Many omega-3 supplements are made from fish or krill, so check the source on the label if you avoid fish. If you are pregnant, breastfeeding or take regular medication, ask your healthcare provider before starting an omega-3 supplement.
Frequently Asked Questions
What is the difference between ALA, EPA and DHA?
ALA is an 18-carbon omega-3 found in plant foods such as flaxseed, chia seeds, walnuts and canola oil, and it is the only omega-3 your body cannot make. EPA and DHA are longer-chain omega-3s found in fish, seafood and algae. The body converts less than 15% of ALA into EPA and DHA.
What are the best food sources of omega-3 fatty acids?
Fatty fish such as salmon, herring, sardines, Atlantic mackerel and trout are rich in EPA and DHA and are on the FDA and EPA list of lower-mercury best choices. Flaxseed oil, chia seeds, walnuts and canola oil are good sources of ALA.
How much omega-3 should I get each day?
The only official U.S. values are Adequate Intakes for ALA: 1.6 g a day for men and 1.1 g a day for women, 1.4 g in pregnancy and 1.3 g during breastfeeding. There is no official U.S. amount for EPA and DHA; the Dietary Guidelines recommend 8 ounces or more of a variety of seafood a week for adults. Ask your healthcare provider about your own needs.
Do omega-3 supplements help memory or brain function?
DHA is a structural part of brain cell membranes, and observational studies link fish-rich diets with better cognitive aging. However, randomized trials in cognitively healthy older adults, such as the two-year OPAL trial, found no difference in cognitive test scores with EPA and DHA supplements. The research is ongoing.
Are omega-3 supplements safe during pregnancy?
Prenatal DHA supplements have been widely studied, and fish intake during pregnancy is recommended by the FDA and EPA from lower-mercury choices. Trials have not shown consistent effects on infant cognition, and needs differ from person to person, so talk with your obstetrician or midwife before taking any supplement during pregnancy.
Sources
- NIH Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Consumers.
- National Center for Complementary and Integrative Health. Omega-3 Supplements: What You Need To Know. 2024.
- U.S. Food and Drug Administration and U.S. Environmental Protection Agency. Advice about Eating Fish. Revised 2021.
- U.S. Food and Drug Administration. Letter of enforcement discretion: petition for a health claim for EPA and DHA (Docket No. FDA-2014-Q-1146). 2019.
- Manson JE, Cook NR, Lee IM, et al. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer. N Engl J Med. 2019.
- Bhatt DL, Steg PG, Miller M, et al. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia. N Engl J Med. 2019.
- Nicholls SJ, Lincoff AM, Garcia M, et al. Effect of high-dose omega-3 fatty acids vs corn oil on major adverse cardiovascular events in patients at high cardiovascular risk: the STRENGTH randomized clinical trial. JAMA. 2020.
- Gencer B, Djousse L, Al-Ramady OT, et al. Effect of long-term marine omega-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021.
- Dangour AD, Allen E, Elbourne D, et al. Effect of 2-y n-3 long-chain polyunsaturated fatty acid supplementation on cognitive function in older people: a randomized, double-blind, controlled trial. Am J Clin Nutr. 2010.
- Makrides M, Gibson RA, McPhee AJ, et al. Effect of DHA supplementation during pregnancy on maternal depression and neurodevelopment of young children: a randomized controlled trial. JAMA. 2010.
- Middleton P, Gomersall JC, Gould JF, et al. Omega-3 fatty acid addition during pregnancy. Cochrane Database Syst Rev. 2018.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
