Short answer. Omega-3s are essential fats. EPA and DHA, the long-chain forms, come mostly from fish, fish oil and algae, because the body turns less than 15% of plant ALA into them (NIH ODS). The US sets an Adequate Intake only for ALA, 1.1 to 1.6 g a day for adults, and no upper limit.
Omega-3 sources and supplement forms at a glance
| Source or form | Main omega-3s | What the research says |
|---|---|---|
| Flaxseed oil, chia seeds, walnuts, canola oil | ALA | Rich in ALA (flaxseed oil 7.26 g per tablespoon), but less than 15% becomes EPA and DHA (NIH ODS) |
| Fatty fish, 3 ounces cooked | EPA and DHA | Farmed Atlantic salmon about 1.83 g, herring 1.71 g, sardines 1.19 g; cod and light tuna much less (NIH ODS) |
| Fish oil, natural triglycerides | EPA and DHA | A typical 1,000 mg capsule gives 180 mg EPA and 120 mg DHA (NIH ODS) |
| Re-esterified triglycerides (rTG) | EPA and DHA, concentrated | 124% of the uptake of natural fish oil in a 2-week trial in 72 volunteers (PMID 20638827) |
| Ethyl esters (EE) | EPA and DHA, concentrated | 73% of the uptake of natural fish oil in the same trial; all forms still raised blood levels (PMID 20638827) |
| Krill oil, phospholipids | Lower EPA and DHA per gram | No good evidence yet that it is absorbed better than fish oil (PMID 25156381) |
| Algal oil | Mostly DHA, triglycerides | 600 mg DHA a day matched cooked salmon in a 2-week trial in 32 adults (PMID 18589030) |
Source: NIH Office of Dietary Supplements and the PubMed abstracts listed under Sources.
What are omega-3s, and how do EPA, DHA and ALA differ?
Omega-3s are a family of polyunsaturated fats. Three get most of the research attention: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are called long-chain omega-3s. ALA is an essential fatty acid: it has to come from food (NIH ODS).
Omega-3s are built into the phospholipids of cell membranes, and DHA is especially concentrated in the retina and the brain. They also provide energy and are used to make eicosanoids, signaling molecules involved in the cardiovascular, immune and endocrine systems (NIH ODS).
ALA is the plant omega-3. The body can turn some of it into EPA and then DHA, mainly in the liver, but reported conversion rates are under 15%, so NIH ODS calls eating EPA and DHA directly the only practical way to raise their levels. Fish do not make EPA and DHA themselves: microalgae do, and fish collect them through the food chain (NIH ODS). That is why algal oil can supply DHA without fish. On labels, compare the milligrams of EPA and DHA, not the weight of oil: a typical 1,000 mg fish oil capsule holds about 300 mg of the two combined.
How much omega-3 do kids and adults need?
US Dietary Reference Intakes set an Adequate Intake (AI) for omega-3s, expressed as ALA from age 1 and as total omega-3s for babies. There is no separate RDA for EPA or DHA, and no Tolerable Upper Intake Level for any omega-3 (NIH ODS).
| Age | Male AI | Female AI | Upper limit (UL) |
|---|---|---|---|
| Birth to 6 months | 0.5 g (total omega-3s) | 0.5 g (total omega-3s) | Not established |
| 7–12 months | 0.5 g (total omega-3s) | 0.5 g (total omega-3s) | Not established |
| 1–3 years | 0.7 g | 0.7 g | Not established |
| 4–8 years | 0.9 g | 0.9 g | Not established |
| 9–13 years | 1.2 g | 1.0 g | Not established |
| 14–18 years | 1.6 g | 1.1 g | Not established |
| Adults 19 and older | 1.6 g | 1.1 g | Not established |
| Pregnancy | — | 1.4 g | Not established |
| Breastfeeding | — | 1.3 g | Not established |
Source: NIH Office of Dietary Supplements (Omega-3 Fatty Acids fact sheet) and the Dietary Reference Intake tables on NCBI Bookshelf. Values are grams per day, as ALA from age 1.
Most Americans meet the ALA target: in national survey data, adults averaged 1.59 g (women) and 2.06 g (men) of ALA a day from food. EPA and DHA from food are a different story: about 40 mg a day in children and teens and about 90 mg a day in adults (NIH ODS). One 3-ounce serving of farmed Atlantic salmon carries about 1,830 mg of the two.
How much EPA and DHA a child needs is a question for their pediatrician.
Can you get enough omega-3 from food alone?
For ALA, usually yes. Flaxseed oil (7.26 g per tablespoon), chia seeds (5.06 g per ounce), English walnuts (2.57 g per ounce), canola oil (1.28 g per tablespoon) and soybean oil (0.92 g per tablespoon) are all rich sources (NIH ODS).
For EPA and DHA, it depends on how often you eat fatty fish. Per 3 ounces cooked, Atlantic herring has 0.94 g DHA and 0.77 g EPA, sardines 0.74 g and 0.45 g, and Atlantic mackerel 0.59 g and 0.43 g, while light canned tuna has 0.17 g and 0.02 g and Pacific cod 0.10 g and 0.04 g (NIH ODS).
The fish's feed matters too: in farmed Atlantic salmon from Scotland, EPA and DHA fell between 2006 and 2015 as fish feed changed (NIH ODS).
Which form of omega-3 supplement is best: triglyceride, ethyl ester, krill or algae?
Triglycerides and ethyl esters. Natural triglycerides are the form in fish oil. Ethyl esters are made from them by swapping glycerol for ethanol, and re-esterified triglycerides are ethyl esters turned back into triglycerides (NIH ODS). In a trial in 72 volunteers who took about 3.3 g of EPA plus DHA a day for 2 weeks, uptake from re-esterified triglycerides was 124% of that from natural fish oil, uptake from ethyl esters was 73%, and free fatty acids (91%) did not differ significantly from natural oil (PMID 20638827). NIH ODS agrees that every form significantly raises blood levels.
Krill oil. Krill oil carries omega-3s mainly as phospholipids, with less EPA and DHA per gram than fish oil and a red color from astaxanthin. A review of the krill studies found none had matched EPA and DHA doses properly and saw no evidence at present that krill oil is absorbed better than fish oil (PMID 25156381).
Algal oil. Algal oil supplements usually provide 100 to 300 mg of DHA, in triglyceride form (NIH ODS). In a 2-week randomized trial, 32 healthy adults aged 20 to 65 took 600 mg of DHA a day either from algal-oil capsules or from cooked salmon. DHA rose by about 80% in plasma phospholipids and about 25% in red blood cells in both groups, and the two sources were judged equivalent (PMID 18589030).
Cod liver oil also supplies vitamin A and vitamin D. NIH ODS reports that omega-3 supplements have not been found to contain methyl mercury, because it is removed during processing and purification.
How should you take and store fish oil so it is absorbed?
- Take it with a meal. Omega-3s are absorbed like other dietary fats, at about 95% (NIH ODS). Several labels below ask for the dose with food or a meal.
- Store it as the label says. The DHA+PC+E liquid below, for example, goes in the refrigerator on receipt.
- Check the date and the seal. Use the oil before the date on the label, keep the cap closed, and if a bottle smells or tastes clearly off, ask the seller or your pharmacist before you keep using it.
- Know the usual side effects. NIH ODS lists an unpleasant taste, bad breath, heartburn, nausea, stomach upset, diarrhea and headache, usually mild.
Can you take too much omega-3?
There is no official upper limit, but the safety reviews give clear reference points. The Institute of Medicine noted that 900 mg of EPA plus 600 mg of DHA a day or more for several weeks might reduce immune function, and that 2 to 15 g a day might lengthen bleeding time. The European Food Safety Authority found that combined EPA and DHA up to about 5 g a day long term appears safe, and FDA has concluded that supplements providing no more than 5 g a day of EPA and DHA are safe when used as recommended (NIH ODS).
A newer signal concerns heart rhythm. A meta-analysis of 7 large cardiovascular trials with 81,210 participants (mean age 65, average follow-up 4.9 years) linked marine omega-3 supplements with a higher risk of atrial fibrillation, an irregular heart rhythm (hazard ratio 1.25). The risk was greater in trials using more than 1 g a day (hazard ratio 1.49) than in trials using 1 g a day or less (hazard ratio 1.12) (PMID 34612056). These were heart-outcome trials in mostly older adults; still, the finding is a good reason to agree any intake above 1 g a day with a doctor.
Does fish oil interact with blood thinners or other medicines?
The main interaction NIH ODS describes is with warfarin and similar anticoagulants. At high doses fish oil has antiplatelet effects, weaker than aspirin, and it might raise the INR, though most research shows that 3 to 6 g a day does not significantly change anticoagulation (NIH ODS).
In a small double-blind trial, 16 people on long-term warfarin took placebo, 3 g or 6 g of fish oil a day for 4 weeks; INR did not change significantly and there was no major bleeding (PMID 10767122). A 2014 review concluded that omega-3s affect platelet function but did not increase clinically significant bleeding, alone or alongside other drugs that affect clotting (PMID 24472372). The prescribing information for prescription omega-3 products still advises periodic INR checks for people on anticoagulants (NIH ODS). If you take warfarin, aspirin or another blood thinner, tell the prescriber before you start, and never change those medicines on your own.
Which ASDHelp products contain omega-3s?
Doses are copied from each label. Every label dose below is well under the 5 g a day FDA figure, but two products can pass 1 g a day of EPA plus DHA, so agree that total with the doctor, and add up EPA and DHA if you combine products.
- Omega-3 Mini: 150 mg EPA and 100 mg DHA (250 mg total omega-3s, as ethyl esters) per small lemon-flavored softgel. Label directions: adults, 1 softgel 1 to 6 times daily with food; children as directed by a healthcare professional. Note: 6 softgels give 900 mg EPA plus 600 mg DHA (1,500 mg), the level the Institute of Medicine flagged for possible immune effects over several weeks.
- Spectrum DHA: 580 mg DHA and 130 mg EPA per softgel, from anchovy, mackerel and sardine oil. Label directions: 1 softgel per day; no children's dose is given.
- DHA+PC+E: 1,200 mg DHA per 2.25 mL serving, with 60 mg phosphatidylcholine and 11 mg (17 IU) vitamin E as mixed tocopherols, from anchovy oil. Label directions: 2.25 mL once a day with a meal; refrigerate after receipt; consult a healthcare professional before any use by minors. The vitamin E is far below the upper limit for every age (lowest: 200 mg at ages 1 to 3).
- Spectrum Neurotransmitter Support: 50 mg DHA from algal oil per scoop (about 17.9 g), in a protein powder with NAC and CoQ10, formulated without fish or shellfish. Label directions are for children 4 years or older, 1 level scoop in 4 to 6 oz of a drink; check with the pediatrician first.
Related reading: vitamin E and CoQ10.
Questions to take to your doctor
- Does our diet already supply enough EPA and DHA, or would a supplement or more fish make sense?
- Would an omega-3 index or fatty acid blood test be useful before we decide, and how should the result be read?
- Given any blood thinners or other medicines we take, what daily total of EPA plus DHA is right, and is more than 1 g a day appropriate?
- For a child, which form (fish oil, liquid or algal DHA) and what amount fit their age and diet?
Sources
- NIH Office of Dietary Supplements. Omega-3 Fatty Acids: fact sheet for health professionals (updated August 22, 2025). ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional
- NIH Office of Dietary Supplements. Vitamin E fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminE-HealthProfessional
- National Academies. Dietary Reference Intakes summary tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Dyerberg J et al. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids 2010. PMID 20638827
- Arterburn LM et al. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. J Am Diet Assoc 2008. PMID 18589030
- Salem N Jr, Kuratko CN. A reexamination of krill oil bioavailability studies. Lipids Health Dis 2014. PMID 25156381
- Bender NK et al. Effects of marine fish oils on the anticoagulation status of patients receiving chronic warfarin therapy. J Thromb Thrombolysis 1998. PMID 10767122
- Wachira JK, Larson MK, Harris WS. n-3 Fatty acids affect haemostasis but do not increase the risk of bleeding. Br J Nutr 2014. PMID 24472372
- Gencer B 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. Circulation 2021. PMID 34612056
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.