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Omega 3 Supplements: Benefits, Dosage and What to Look For

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The OneVit Team

The OneVit Team

Updated on

15th May 2026

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9 min

Omega 3 Supplements: Benefits, Dosage and What to Look For

Omega 3 supplements are among the most widely taken in the UK, and for good reason. The fatty acids they contain, EPA and DHA, play a structural role in nearly every cell in the body. But with dozens of products on shelves and a lot of conflicting information online, it can be hard to know what to look for. This guide covers what EPA and DHA actually do, how much to take, the difference between fish oil and plant-based options, and what to check before you buy.

What are omega 3 supplements?

Omega 3 fatty acids are a family of polyunsaturated fats that the body cannot make in adequate amounts on its own. There are three main types relevant to human health:

Alpha-linolenic acid (ALA) is found in plant foods such as flaxseeds, chia seeds, walnuts, and rapeseed oil. It's the only omega 3 classified as essential, meaning it must come from food or supplements. The body can convert some ALA into EPA and DHA, but this conversion is slow and inefficient - typically less than 10% for EPA, and often less than 1% for DHA.1

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the long-chain omega 3 fatty acids responsible for most of the health benefits associated with omega 3 intake. They are found in oily fish, seafood, and microalgae. Because the body produces only small amounts from ALA, EPA and DHA also need to come from diet or supplementation if intake is to be meaningful.2

Omega 3 supplements in the UK most commonly provide EPA and DHA in the form of fish oil capsules, but plant-based algae oil products are available and growing in popularity.

What do EPA and DHA do in the body?

EPA and DHA are structural components of cell membranes throughout the body, particularly in the brain, retina, and cardiovascular system. They help maintain membrane fluidity and support cell signalling, and they serve as precursors to lipid compounds that help regulate inflammatory processes.

At a daily intake of 250mg, EPA and DHA together contribute to the normal function of the heart. DHA specifically contributes to normal brain function and normal vision at the same daily intake.3

Research has explored omega 3's potential role in a wider range of areas. Some observational studies suggest associations between higher intake and joint comfort, skin health, and mood, though intervention trials in these areas have produced mixed results. It's worth noting that NICE guidance (NG238) does not recommend omega 3 supplements for primary or secondary prevention of cardiovascular disease in the general population. They relate to normal physiological function, not the treatment or prevention of heart disease.4

Who may benefit from omega 3 supplements?

The NHS recommends eating at least two portions of fish per week, one of which should be oily fish such as salmon, mackerel, sardines, or herring.5 A typical portion of oily fish provides around 1 to 2g of EPA and DHA. For people who regularly hit this target, diet alone may be enough.

Those most likely to benefit from supplementation include:

People who eat little or no fish. This includes many vegans and vegetarians, those allergic to fish, as well as people who simply dislike it. Without oily fish in the diet, EPA and DHA intake from food sources alone is typically very low.

People following plant-based diets. Plant foods provide ALA but not EPA or DHA directly. Because conversion from ALA is limited, dedicated EPA and DHA supplementation, ideally from algae oil, is a good idea.

Pregnant and breastfeeding women. DHA plays a role in foetal brain and eye development, and in infants too. The NHS recommends pregnant women eat two portions of fish weekly but advises avoiding certain species high in mercury (shark, swordfish, marlin) and limiting tuna. Women should not take fish liver oil supplements during pregnancy due to the risk of excessive vitamin A. Standard fish oil or algae oil is the most appropriate form.5

Older adults. Dietary surveys suggest that EPA and DHA intake tends to decline with age, and this group may benefit from maintaining consistent intake through supplementation.

If you are taking prescription medication, particularly anticoagulants such as warfarin, speak to your GP before starting omega 3 supplements, as higher doses may affect blood clotting.6

How much omega 3 should you take per day?

There is no formal Reference Nutrient Intake (RNI) for EPA and DHA in the UK. However, guidance from several authoritative bodies provides a general baseline:

  • The European Food Safety Authority (EFSA) recommends a combined EPA and DHA intake of 250mg per day for general cardiovascular health maintenance in adults.7
  • The British Heart Foundation suggests aiming for approximately 450mg per day of EPA and DHA combined, equivalent to eating the NHS-recommended two portions of fish weekly.8
  • EFSA considers supplemental intakes of up to 5g per day of combined EPA and DHA safe for adults, but doses above 3g should only be considered under medical supervision due to potential effects on blood pressure and clotting.7

A practical note on labels: a product described as "1,000 mg fish oil" typically does not contain 1,000 mg of EPA and DHA. The fish oil total includes other fats. The actual EPA and DHA content is usually far lower - often around 300 mg combined in a standard capsule. Always look for the EPA and DHA figures specifically on the label, not the total fish oil amount.

For most adults taking a supplement to support general health and bridge a dietary gap, a product providing 250 to 500 mg of combined EPA and DHA daily is appropriate.

Fish oil, krill oil and algae: what's the difference?

Most omega 3 supplements on the UK market fall into three categories:

Fish oil

The most common source. Derived from oily fish such as anchovies, sardines, or mackerel. Provides a good balance of EPA and DHA, is widely studied, and tends to be the most cost-effective option. Look for products that specify EPA and DHA content per serving and carry a sustainability certification - from the MSC (Marine Stewardship Council) as an example.

Krill oil

Derived from small crustaceans. EPA and DHA in krill oil are bound to phospholipids rather than triglycerides, which some research suggests may improve absorption, though evidence is not conclusive. Krill oil also contains a natural antioxidant called astaxanthin. It's generally more expensive per milligram of EPA and DHA than fish oil.

Algae oil

Microalgae is the original source of EPA and DHA in the marine food chain. Fish accumulate these fatty acids by eating algae. Algae-derived supplements provide EPA and DHA directly, without any animal products, making them the suitable choice for vegans and vegetarians. Quality varies between brands, so check the EPA and DHA content per serving carefully, as some algae products provide primarily DHA with limited EPA.

OneVit Omega 3 provides a daily dose of combined EPA and DHA from high-quality fish oil, with clear label transparency on the exact EPA and DHA content per capsule.

For those who want to support skin structure alongside omega 3 intake, OneVit Marine Collagen Complex pairs well. Collagen and omega 3 work on different aspects of skin health, with omega 3 supporting the fatty acid composition of skin cell membranes and collagen providing structural protein support.

What to look for when buying omega 3 supplements

With a crowded market, these are the practical things to check before you buy:

EPA and DHA content per serving. This is the most important figure on the label. Ignore the total fish oil or total omega 3 figure. You want to see the exact EPA and DHA milligrams listed separately and clearly.

Sustainability certification. Look for the MSC blue tick (for fish-derived products) or a responsible sourcing statement. Sustainable sourcing matters for the environment and often is closely related with production quality.

Third-party testing. Fish oil can accumulate environmental contaminants such as heavy metals and PCBs (polychlorinated biphenyls). Reputable manufacturers test for these independently and publish results. Look for products that mention molecular distillation or independent purity testing.

Form and format. Softgel capsules are the most common and convenient option. Liquid fish oils provide higher doses per serving but require refrigeration and can oxidise quickly once opened. If fish oil causes a fishy aftertaste, try taking capsules with food or choosing an enteric-coated product.

Expiry and oxidation. Omega 3 oils oxidise over time and can become rancid. Cut a capsule open occasionally. If it smells strongly fishy or unpleasant rather than mildly "oceanic", it may be oxidised. Store supplements away from heat and direct light.

Are omega 3 supplements safe? Side effects to know about

For most people, omega 3 supplements at standard doses (250 to 500 mg EPA and DHA daily) are well tolerated. The most commonly reported side effect is a fishy aftertaste or mild digestive discomfort, which can usually be reduced by taking capsules with meals.

At higher doses (above 3g daily), there is evidence of an increased risk of atrial fibrillation in people with existing cardiovascular conditions.4 High-dose supplementation should only be undertaken under medical supervision.

People taking anticoagulant medication such as warfarin should have their INR monitored when starting omega 3, as the fatty acids can have a mild effect on blood clotting at higher doses.6

Pregnant women should avoid cod liver oil supplements specifically, as these contain high amounts of vitamin A (retinol), which can be harmful to foetal development at elevated levels. Standard fish oil supplement, which are not derived from the liver, don't carry the same risk.5

Frequently Asked Questions

What is the difference between omega 3, 6 and 9? Omega 3, 6, and 9 refer to different families of polyunsaturated and monounsaturated fatty acids, named after the position of their first double bond. Omega 6 is found mainly in vegetable oils and is already consumed in high amounts in most Western diets. The concern isn't that people get too little omega 6 - it's that the ratio of omega 6 to omega 3 tends to be too high. Omega 9 (found in olive oil) is not essential as the body can make it. Supplements labelled "omega 3-6-9" are not necessarily superior. In most cases, omega 3 supplementation alone is what is relevant for people with low EPA and DHA intake.

Can you take omega 3 supplements every day? Yes. Daily supplementation is the standard approach and consistent intake is important for maintaining adequate EPA and DHA levels. There is no evidence of harm from taking omega 3 daily at doses within standard supplementation ranges (up to 3g per day of combined EPA and DHA for adults).

When is the best time to take omega 3 supplements? With a meal containing some fat is generally recommended, as omega 3 fatty acids are fat-soluble and absorption is improved in the presence of dietary fat. This also reduces the likelihood of a fishy aftertaste.

Do vegan omega 3 supplements work as well as fish oil? Algae oil supplements provide EPA and DHA directly and are biochemically equivalent to those from fish oil: fish accumulate EPA and DHA from algae in the first place. They're a suitable alternative for anyone avoiding fish products. Some algae supplements provide primarily DHA rather than a balanced EPA and DHA dose, so check the label to confirm both are included.

Is fish oil the same as omega 3? Fish oil is one source of omega 3 fatty acids, specifically EPA and DHA. Not all omega 3 products are fish oil (algae oil is a plant-based alternative), and not all fish oil products contain the same amount of EPA and DHA. The omega 3 content that matters is the EPA and DHA figure, not the total fish oil milligrams.

How long does it take for omega 3 supplements to work? Blood levels of EPA and DHA typically rise within a few weeks of consistent supplementation. For any noticeable effects on markers such as triglyceride levels, studies typically use supplementation periods of 8 to 12 weeks or longer. Omega 3 is best thought of as a long-term nutritional support rather than a short-term supplement.

Can you get too much omega 3? EFSA considers up to 5g per day of combined EPA and DHA safe for most adults. Doses above 3g are not recommended without medical supervision. Excess omega 3 from food sources alone is not a major concern for most people in the UK.

References

  1. Burdge GC, Calder PC. Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reproduction, Nutrition, Development. 2005;45(5):581–597. https://doi.org/10.1051/rnd:2005047
  2. British Dietetic Association. Omega-3. BDA Food Fact Sheet. April 2021. https://www.bda.uk.com/resource/omega-3.html
  3. Great Britain Nutrition and Health Claims (NHC) Register. Department of Health and Social Care. Updated February 2025. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
  4. National Institute for Health and Care Excellence. Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238). 2023. https://www.nice.org.uk/guidance/ng238
  5. NHS. Fish and shellfish. https://www.nhs.uk/live-well/eat-well/food-types/fish-and-shellfish-nutrition/
  6. European Food Safety Authority. Scientific opinion on the tolerable upper intake level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Journal. 2012;10(7):2815. https://doi.org/10.2903/j.efsa.2012.2815
  7. European Food Safety Authority. Dietary reference values for fats. EFSA Journal. 2010;8(3):1461. https://doi.org/10.2903/j.efsa.2010.1461
  8. British Heart Foundation. Omega-3s and your heart. Heart Matters. October 2025. https://www.bhf.org.uk/informationsupport/heart-matters-magazine/nutrition/omega-3s-and-your-heart

This article is for informational purposes only and does not constitute medical advice. If you are concerned about your omega 3 intake or have an underlying health condition, consult a GP or qualified healthcare professional.

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