Omega-3: How Much You Need, Which to Choose and Who It Really Helps

Omega-3 has become a kind of grown-up vitamin: “for the heart”, “for the brain”, “for joints”, “for skin”. People take capsules for years believing it insures them against a heart attack. As a doctor, I have to say the picture is more complicated than the ads suggest.

Below I cover what large trials in tens of thousands of people actually showed and how to choose a supplement if you really need one.

What omega-3 is: ALA, EPA and DHA

The word “omega-3” covers three main fatty acids. ALA (alpha-linolenic acid) is found in flaxseed oil, chia seeds and walnuts. EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) come mainly from fish and seafood. Most heart and brain research has studied EPA and DHA.

The body can convert ALA into EPA and DHA, but very poorly: only a few percent becomes EPA and even less becomes DHA. So a spoon of flaxseed oil does not replace fish, even though it is healthy in its own right.

DHA is part of the cell membranes in the brain and retina, which is why it matters so much for babies during pregnancy and early life. EPA is more involved in inflammation and blood fat metabolism.

How much omega-3 you need a day

The European Food Safety Authority considers 250 mg of EPA and DHA combined per day adequate for adults. For pregnant and breastfeeding women it advises an extra 100-200 mg of DHA. In practice, that means one or two servings of oily fish a week.

EFSA also assessed the upper limit: supplements of up to 5 g of EPA and DHA a day raise no safety concerns in adults. But “safe” here does not mean “beneficial”, and you will see why below.

Figures are approximate, based on USDA FoodData Central: content varies with season, feed and cooking. During pregnancy, choose small oily fish (mackerel, herring, sardines, salmon) and limit large predatory fish such as swordfish and king mackerel because of mercury.

Omega-3 and the heart: what large trials showed

The idea seemed logical: populations that eat lots of fish have fewer heart attacks, so fish oil capsules should protect the heart. But when this was tested in randomized trials, the results were more modest.

VITAL (2019). More than 25,000 healthy people in the US took 1 g of omega-3 a day or placebo for five years. The combined number of heart attacks, strokes and cardiac deaths did not fall. Heart attacks alone were somewhat fewer, but that was a secondary outcome and cannot be relied on with confidence.

ASCEND (2018). 15,000 people with diabetes took the same 1 g a day for almost 7.5 years. No difference from placebo.

REDUCE-IT (2019). Patients with high triglycerides already on statins received 4 g of purified EPA (the prescription drug icosapent ethyl). Cardiac events fell by 25%. But the placebo was mineral oil, which may itself have worsened outcomes, so some experts believe the effect was overstated.

STRENGTH (2020). Similar patients, 4 g of an EPA and DHA mix, with corn oil as placebo. The trial was stopped early because it found no benefit.

A 2020 Cochrane review of 86 trials with more than 160,000 participants concluded that omega-3 has little or no effect on overall or cardiovascular mortality, but lowers triglycerides by about 15%.

There is also a side effect worth knowing about. A 2021 meta-analysis in Circulation found that omega-3 supplements raise the risk of atrial fibrillation by about 25%, and by almost 50% at doses above 1 g a day. So “more is better” does not apply to omega-3.

Brain, eyes, joints, pregnancy: where the benefits are

Pregnancy. This is where the evidence is strongest. A 2018 Cochrane review found that omega-3 during pregnancy reduces the risk of preterm birth before 37 weeks by about 11%, and very early birth before 34 weeks by about 42%. That is a strong argument for pregnant women who rarely eat fish.

Triglycerides. High doses (2-4 g a day) lower them by 20-30%. But that is treatment chosen by a doctor, not a do-it-yourself course.

Dry eyes. The large DREAM trial in 2018 found no difference between omega-3 and placebo. Unfortunately, many patients are still advised to take capsules for exactly this.

Depression. Results are mixed. Some studies see a small benefit from EPA-dominant products as an add-on to treatment, but omega-3 cannot replace antidepressants or psychotherapy.

Joints. In rheumatoid arthritis, omega-3 may slightly reduce morning stiffness and the need for painkillers. For ordinary osteoarthritis the evidence is weak.

Memory in older age. Large trials have not shown that omega-3 supplements prevent dementia. Observational data suggest fish on the plate does more than capsules.

How to choose omega-3: forms and labels

Rule one: count the EPA and DHA per daily serving. A label saying “fish oil 1000 mg” tells you almost nothing on its own. Ordinary fish oil is only about 30% omega-3, so 300 mg per capsule. Concentrates provide 600-900 mg. In Ukraine, supplements must now state content per recommended daily serving, as we explained in our article on Order No. 203.

Rule two: freshness. Omega-3 oxidizes easily. Quality manufacturers state the peroxide value and TOTOX, and the industry body GOED recommends TOTOX no higher than 26. A sharp rancid fish smell from an open bottle is a bad sign.

Rule three: purity. Fish oil is purified of mercury, dioxins and PCBs. Look for independent testing certificates (such as IFOS) or heavy metal data.

And about label claims. In the EU, it is allowed to say that EPA and DHA contribute to normal heart function (at 250 mg a day) and that DHA supports normal brain function and vision. Claims like “prevents heart attacks” or “treats depression” break the rules for food supplements.

How to take omega-3 properly

Who benefits from a supplement. People who hardly eat fish. Pregnant and breastfeeding women without fish in their diet. Vegans (algal oil). Patients with high triglycerides, on a doctor’s advice. If you eat oily fish twice a week, capsules usually add nothing.

Dose. For general support, 250-500 mg of EPA and DHA a day. During pregnancy, 200-300 mg of DHA on top of the diet. Avoid 1 g or more without a specific reason and a doctor, given the atrial fibrillation risk.

Timing. With a meal that contains fat. Ethyl esters are absorbed several times worse on an empty stomach. Morning or evening does not matter, so take it when you will remember. If you also take vitamin D, it is convenient to take them together, since both are fat-soluble.

Fishy burps. Taking capsules mid-meal, choosing enteric-coated capsules and keeping them in the fridge all help. If the burps smell rancid, the product may be oxidized.

Who should be careful. If you take anticoagulants or antiplatelet drugs (warfarin, apixaban, clopidogrel, aspirin), agree the dose with your doctor. People with a history of atrial fibrillation should avoid high doses. If you are allergic to fish, choose algal oil. Tell your doctor about omega-3 before planned surgery.

Omega-3 is often bought together with magnesium and zinc. There is no conflict between them. But each supplement makes sense only for its own reason, and combining them adds nothing extra.

Frequently asked questions

Conclusions

Adults need about 250 mg of EPA and DHA a day. Two servings of oily fish a week provide that without supplements.

A 1 g omega-3 capsule does not protect people without heart disease from heart attacks, and high doses raise the risk of atrial fibrillation. The best evidence of benefit is in pregnancy (fewer preterm births) and for lowering triglycerides under medical supervision.

If you choose a supplement, count the EPA and DHA per daily serving, check freshness and purity, take it with fatty food and don’t exceed 1 g a day without a doctor.

About the Author

Nikolay Bondarenko is a Ukrainian dermatologist and expert in skin diseases.   A graduate of Ukraine's leading medical university, he specializes in diagnosing and treating dermatological issues.   As the author of numerous expert articles, he actively contributes to the development of dermatology and shares his knowledge with the medical community.