By Nikola · Precision Nutrition L1 · Updated 5 November 2026
Fish oil is a supplement made from the fat of oily fish that provides the long-chain omega-3 fats EPA and DHA; a typical 1,000 mg capsule contains about 180 mg EPA and 120 mg DHA, close to the 250 mg a day that EFSA sets as the adequate intake for adults. The clearest evidence is for lowering blood triglycerides, at about 2 g of EPA and DHA a day or more. For preventing heart attacks and strokes in people without heart disease, large trials such as VITAL found no clear benefit from 1 g a day. High doses slightly raise the risk of atrial fibrillation and can affect bleeding, and cod liver oil adds a lot of vitamin A. For omega-3 in food, see omega-3 fatty acids.
What the research says
- Triglycerides (strong evidence). A 2020 Cochrane review of 86 trials with 162,796 people found that long-chain omega-3s lower triglycerides by about 15%. The EU allows “DHA and EPA contribute to the maintenance of normal blood triglyceride levels” for foods providing 2 g of EPA and DHA a day, and “DHA and EPA contribute to the maintenance of normal blood pressure” at 3 g a day.
- Heart attacks and strokes in the general population (weak evidence for benefit). In VITAL, 25,871 US adults took 1 g a day or placebo for about 5.3 years: no significant drop in major cardiovascular events, stroke or cardiovascular death, although total heart attacks were 28% lower. ASCEND, in 15,480 people with diabetes, also found no effect. Cochrane found slight reductions in cardiovascular deaths and coronary events, and no effect on overall mortality or stroke.
- High-dose purified EPA in high-risk people (moderate evidence, prescription only). In REDUCE-IT, 8,179 people took 4 g a day of icosapent ethyl, a prescription form of EPA, and had 25% fewer cardiovascular events than with a mineral oil placebo; the NIH notes that mineral oil is not a neutral placebo, so the benefit may be overstated. STRENGTH, with 4 g of a different EPA and DHA product against corn oil, was stopped early with no benefit.
- Pregnancy (moderate evidence). A 2018 Cochrane review, as summarised by the NIH, found 11% fewer preterm births and 42% fewer early preterm births with long-chain omega-3s. EFSA advises an extra 100-200 mg of DHA a day in pregnancy and breastfeeding.
- Joints and dry eye (weak or mixed). In rheumatoid arthritis, people needed fewer painkillers, with no consistent effect on pain or stiffness (NIH). For dry eye, the NIH-funded DREAM study found fish oil no better than placebo (NCCIH).
- Memory, depression, macular degeneration (no clear benefit). No effect on cognition in healthy older adults or Alzheimer’s disease, uncertain evidence for depression, and no extra benefit when added to the AREDS2 eye formula.
Dose and forms
| Reference point | EPA + DHA per day | Source |
|---|---|---|
| Adequate intake, adults | 250 mg | EFSA |
| EU heart function claim | 250 mg | Regulation (EU) 432/2012 |
| For people with coronary heart disease | about 1 g, preferably from food | American Heart Association, via NIH |
| EU triglyceride claim / blood pressure claim | 2 g / 3 g | Regulation (EU) 432/2012 |
| Supplemental intake considered safe | up to about 5 g | EFSA; the EU requires supplements with the 2 g and 3 g claims to warn not to exceed 5 g |
Forms. Natural or re-esterified triglycerides, ethyl esters, free fatty acids or phospholipids. Triglyceride and free fatty acid forms are somewhat better absorbed than ethyl esters, but all raise EPA and DHA in the blood (NIH). Krill oil is mostly phospholipids, with mixed evidence on absorption. Algae oil, the vegetarian option, usually gives 100-300 mg DHA per serving, sometimes with EPA. Cod liver oil also contains vitamins A and D (see below). Fish oil supplements have not been found to contain methylmercury, which is removed in processing (NIH).
Food sources
| Product | EPA + DHA, 100 g | Portion | EPA + DHA per portion |
|---|---|---|---|
| Atlantic mackerel, raw | 2.30 g | 85 g | 1.95 g |
| Atlantic salmon, farmed, raw | 1.96 g | 85 g | 1.67 g |
| Sardines, canned in oil | 0.98 g | 1 tin, 92 g | 0.90 g |
| Cod liver oil | 17.9 g | 1 tsp, 4.5 g | 0.81 g (plus 1,350 µg vitamin A and 11 µg vitamin D) |
| Typical fish oil capsule (NIH) | – | 1 capsule, 1,000 mg | 0.30 g |
Source: USDA FoodData Central, SR Legacy, checked 5 November 2026: mackerel FDC 175119, salmon FDC 175167, sardines FDC 175139, cod liver oil FDC 173577; EPA + DHA is the sum of the two values. Capsule: NIH ODS. Values per portion are calculated and rounded; products vary.
One 85 g portion of mackerel or salmon gives more EPA and DHA than five typical capsules, and a tin of sardines about as much as three. Anchovies, canned tuna and the plant ALA sources flaxseed, walnuts and chia are covered in the omega-3 entry.
Side effects and interactions
- Common, mild effects. Unpleasant taste, bad breath, heartburn, nausea, stomach discomfort, diarrhoea, headache and smelly sweat (NIH, NCCIH).
- Atrial fibrillation. A 2021 meta-analysis of 7 trials with 81,210 people found a 25% higher risk of atrial fibrillation with marine omega-3 supplements: 49% higher in trials using more than 1 g a day, 12% at 1 g or less.
- Bleeding. High doses have an antiplatelet effect, weaker than aspirin, and 2-15 g a day may lengthen bleeding time. Most studies find 3-6 g a day does not significantly change warfarin anticoagulation, but prescription omega-3 labels advise regular INR checks (NIH).
- Vitamin A in cod liver oil. A teaspoon in the USDA record has 1,350 µg of vitamin A. The NHS advises no more than 1.5 mg (1,500 µg) a day from supplements, including fish liver oil, and none if you eat liver every week; in pregnancy it advises avoiding liver. See vitamin A and vitamin D.
- Oxidation. Fish oil can go rancid. Studies of shop-bought products disagree: a 2015 New Zealand study reported that many exceeded oxidation limits, while a 2017 analysis of 47 products by the industry body GOED found 77% within its total oxidation limit (TOTOX under 26).
Who should avoid it
- People on blood thinners or with a bleeding disorder, unless a doctor agrees and monitors.
- People with atrial fibrillation or other rhythm problems: discuss any dose above 1 g a day with a cardiologist. Before surgery, tell the surgeon you take it.
- Anyone who eats liver weekly should skip cod liver oil (NHS advice on vitamin A supplements); in pregnancy, ask your midwife or doctor before any fish liver oil.
- People with a fish allergy: ask a doctor first; algae oil is fish-free.
- Anyone without a medical reason: the American Heart Association does not recommend omega-3 supplements for people not at high cardiovascular risk (NIH), and one or two portions of oily fish a week cover the EFSA intake.
How to choose a good product
- Read EPA and DHA per capsule, not “fish oil 1,000 mg”.
- Cod liver oil? Add its vitamin A to any multivitamin.
- Oxidation data: a published TOTOX under 26 meets the voluntary GOED limit.
- Look for independent testing. Seals from U.S. Pharmacopeia, NSF International or ConsumerLab.com show a product contains what the label says and no harmful levels of contaminants; the NIH notes they do not prove safety or effect.
- Vegetarian or vegan? Choose algae oil and check its DHA and EPA. We do not recommend brands or link to shops.
FAQ
What is fish oil good for?
The best evidence is for lowering high triglycerides, usually with 2 g or more of EPA and DHA a day. For preventing heart attacks in healthy people, large trials such as VITAL found no clear benefit; evidence for joints, dry eye, memory and mood is weak or mixed.
How much fish oil should I take a day?
Count EPA and DHA, not fish oil: EFSA’s adequate intake for adults is 250 mg a day, about one typical 1,000 mg capsule. Higher doses for triglycerides should be agreed with a doctor, and EFSA considers supplemental intakes up to about 5 g a day safe.
Is fish oil the same as omega-3?
Not quite. Omega-3 is the family of fats, including plant ALA; fish oil is one source of two of them, EPA and DHA. Algae oil also provides DHA and sometimes EPA without fish.
Related entries and articles
- Omega-3 fatty acids – foods and EFSA intake
- Salmon, mackerel, sardines and anchovies
- Vitamin A and vitamin D
- All about high-quality fats
- Which foods reduce inflammation naturally?
- Recipe: Mediterranean mackerel stew with tomatoes and olives
- Recipe: baked salmon with root vegetables
Sources
- NIH Office of Dietary Supplements: Omega-3 Fatty Acids, Fact Sheet for Health Professionals. ods.od.nih.gov
- NCCIH: Omega-3 Supplements: What You Need To Know. nccih.nih.gov
- Gencer B, et al. (2021). Effect of long-term marine omega-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes. Circulation 144(25):1981-1990. boris.unibe.ch
- EFSA (2017). Dietary Reference Values for nutrients, Summary report (EPA + DHA adequate intake). efsa.europa.eu
- Commission Regulation (EU) No 432/2012 – permitted health claims. legislation.gov.uk
- NHS: Vitamins and minerals – Vitamin A. nhs.uk
- FoodNavigator (2017): Most NZ fish oil supplements meet label claims, oxidation levels – GOED analysis. foodnavigator.com
- NIH Office of Dietary Supplements: Dietary Supplements – What You Need to Know. ods.od.nih.gov
- USDA FoodData Central, SR Legacy: mackerel (FDC 175119), salmon (FDC 175167), sardines (FDC 175139), cod liver oil (FDC 173577). fdc.nal.usda.gov
This page is for information only and is not medical or dietary advice.
