Omega-3 fatty acids—eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA)—are essential polyunsaturated fats vital for cardiovascular health, brain function, and inflammatory regulation. Because the body cannot synthesise these efficiently, they must be obtained through diet or supplementation. The NHS recommends at least two portions of fish weekly, including one portion of oily fish such as salmon or mackerel. The European Food Safety Authority (EFSA) suggests 250 mg of combined EPA and DHA daily for cardiovascular maintenance in adults. Individual requirements vary based on age, health status, and dietary patterns, with therapeutic doses differing for specific conditions. Always consult a healthcare professional before starting supplementation.

What Is the Recommended Daily Dose of Omega-3?

Omega-3 fatty acids are essential polyunsaturated fats that play crucial roles in cardiovascular health, brain function, and inflammatory regulation. The three main types are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA). Because the body cannot synthesise these fatty acids efficiently, they must be obtained through diet or supplementation.

General population recommendations vary between organisations, but the NHS advises consuming at least two portions of fish per week, including one portion of oily fish (such as salmon, mackerel, or sardines). A typical portion of oily fish can provide between 1.5-3.5g of EPA and DHA combined, though this varies by species. The European Food Safety Authority (EFSA) suggests a daily intake of 250 mg of EPA plus DHA for cardiovascular health maintenance in adults. For ALA, found in plant sources like flaxseeds and walnuts, EFSA recommends an adequate intake of approximately 0.5% of total energy intake (about 1.1-1.4g daily for most adults).

Pregnancy and lactation require consideration of omega-3 intake to support foetal brain and eye development. The EFSA recommends an additional 100–200 mg of DHA daily during pregnancy and breastfeeding. However, pregnant women should avoid high-mercury fish (shark, swordfish, and marlin), limit tuna to no more than two tuna steaks or four medium-sized cans per week, and consume no more than two portions of oily fish weekly. Pregnant women should also avoid cod liver oil supplements due to their high vitamin A content, which may harm the developing baby.

For individuals who do not consume fish regularly, supplementation may be considered, though dietary sources are generally preferred. Standard maintenance doses typically range from 250–500 mg of combined EPA and DHA daily. It is important to note that these are general guidelines, and individual requirements may vary based on age, health status, and dietary patterns. Always consult with a healthcare professional before starting supplementation, particularly if you have existing medical conditions or take medications.

Omega-3 Dosage for Different Health Conditions

Therapeutic doses of omega-3 fatty acids may differ substantially from general maintenance recommendations, depending on the specific health condition being addressed. It's important to distinguish between food supplements and prescription omega-3 medicines, which have different regulatory standards and approved uses.

Cardiovascular disease prevention and management guidance has evolved based on recent evidence. Current NICE guidance (NG238) advises not to offer omega-3 fatty acid compounds for primary or secondary prevention of cardiovascular disease. However, NICE Technology Appraisal 805 recommends icosapent ethyl (a purified EPA prescription medicine) at a dose of 2g twice daily with statins for a specific group of high-risk adults with raised triglycerides despite statin therapy. For hypertriglyceridaemia, prescription omega-3 preparations containing 2–4g of EPA and DHA daily may be recommended by specialists, as these doses have demonstrated significant triglyceride-lowering effects. It should be noted that mixed EPA/DHA products (omega-3-acid ethyl esters) may increase LDL cholesterol in some patients, while high-dose EPA (icosapent ethyl) has been associated with increased risk of atrial fibrillation in clinical trials.

Rheumatoid arthritis and inflammatory conditions have been studied with omega-3 supplementation. Research has used doses ranging from 2.6–6g of EPA plus DHA daily, with some patients experiencing reduced joint pain and stiffness. However, evidence is inconsistent, and omega-3 supplementation should complement, not replace, conventional disease-modifying treatments prescribed by rheumatologists. NICE does not routinely recommend omega-3 supplements for these conditions.

Mental health conditions, including depression and cognitive decline, have been investigated with varying results. Some studies have explored doses of 1–2g of EPA daily for depression, with modest benefits reported in some cases as adjunctive therapy. However, evidence remains inconsistent, and NICE does not currently recommend omega-3 supplements as a treatment for depression or cognitive decline.

Dry eye syndrome has been studied with omega-3 supplementation at doses of 1–3g daily of EPA plus DHA, though evidence is mixed and not conclusive enough for routine recommendation.

It is essential to emphasise that therapeutic doses should only be initiated following consultation with a GP or specialist, as higher doses may interact with medications and require monitoring. Prescription omega-3 medicines should be used according to their licensed indications and dosing as specified in their Summary of Product Characteristics.

How to Choose the Right Omega-3 Supplement

Selecting an appropriate omega-3 supplement requires consideration of several factors, including formulation type, purity, concentration, and third-party verification. The UK supplement market offers numerous products with varying quality and composition.

Formulation types include fish oil, krill oil, cod liver oil, and algal oil (suitable for vegetarians and vegans). Fish oil supplements are the most common and typically provide EPA and DHA in triglyceride or ethyl ester forms. Some evidence suggests triglyceride forms may be better absorbed than ethyl esters, though these differences tend to diminish when supplements are taken with meals. Krill oil contains omega-3s in phospholipid form, while algal oil provides a sustainable, plant-based source of DHA and some EPA, making it suitable for those following vegetarian or vegan diets. Pregnant women should avoid cod liver oil supplements due to their high vitamin A content, which may harm the developing baby.

Concentration and dosage should be clearly stated on the label. Many supplements list total fish oil content (e.g., 1000 mg) but contain only 300–500 mg of actual EPA and DHA combined. Always check the specific amounts of EPA and DHA per capsule to ensure you are meeting your target dose without taking excessive numbers of capsules.

Purity and quality standards are paramount, as fish oils can contain environmental contaminants such as mercury, polychlorinated biphenyls (PCBs), and dioxins. Look for products that have undergone molecular distillation or other purification processes. Third-party certifications from organisations such as the International Fish Oil Standards (IFOS) programme provide independent verification of purity and potency, though these are optional and do not replace regulatory oversight. In the UK, most omega-3 products are classified as food supplements rather than medicines.

Freshness indicators include checking the expiration date and looking for products with added antioxidants (such as vitamin E) to prevent oxidation. A strong fishy odour or taste may indicate rancidity, which reduces efficacy and may cause gastrointestinal discomfort.

Sustainability considerations are increasingly important. Look for products certified by the Marine Stewardship Council (MSC) or similar organisations, ensuring fish sources are sustainably harvested. When purchasing supplements, consider reputable brands available through pharmacies or registered online retailers to ensure product authenticity and quality assurance.

Safety and Side Effects of Omega-3 Supplements

Omega-3 supplements are generally well tolerated at recommended doses, but potential adverse effects and drug interactions warrant careful consideration, particularly at higher therapeutic doses.

Common side effects are typically mild and gastrointestinal in nature. These include fishy aftertaste, belching, nausea, loose stools, and indigestion. Taking supplements with meals or choosing enteric-coated formulations can minimise these effects. Some individuals may experience mild headaches or a fishy body odour at higher doses. Freezing capsules before consumption or selecting high-quality, purified products may reduce gastrointestinal symptoms.

Bleeding risk is a consideration, particularly at doses exceeding 3g daily of EPA plus DHA, though clinically significant bleeding is uncommon at standard doses. Omega-3 fatty acids possess antiplatelet properties, potentially prolonging bleeding time. The European Food Safety Authority considers intakes up to 5g/day of EPA plus DHA generally safe for adults, but caution is still warranted in certain groups. Individuals taking anticoagulants (such as warfarin, apixaban, or rivaroxaban) or antiplatelet medications (including aspirin, clopidogrel, or prasugrel) should consult their GP or anticoagulation clinic before starting omega-3 supplementation. Similarly, those scheduled for surgery should inform their surgical team, as some practitioners recommend discontinuing supplements 1–2 weeks pre-operatively.

Allergic reactions can occur in individuals with fish or shellfish allergies, though reactions to highly purified fish oil are uncommon. Those with known allergies should consider algal oil alternatives or discuss options with an allergist. Cod liver oil supplements warrant particular caution due to high vitamin A and D content, which can lead to toxicity if taken in excess, particularly during pregnancy.

Drug interactions extend beyond anticoagulants. Omega-3 supplements may modestly lower blood pressure, potentially enhancing effects of antihypertensive medications. Individuals with diabetes should monitor blood glucose levels, as high doses may slightly affect glycaemic control, though evidence is inconsistent. High-dose EPA (icosapent ethyl) has been associated with an increased risk of atrial fibrillation in clinical trials.

When to seek medical advice: Contact your GP if you experience persistent gastrointestinal symptoms, unusual bruising or bleeding, allergic reactions (rash, swelling, difficulty breathing), or if you are taking multiple medications. If you suspect an adverse reaction to an omega-3 supplement, report it through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk). Pregnant women, breastfeeding mothers, children, and individuals with chronic health conditions should always consult a healthcare professional before starting omega-3 supplementation to ensure safety and appropriate dosing.

Frequently Asked Questions