Short answer up front
Omega-3 is a family of essential fats your body can’t make. The three that matter are ALA (from plants), EPA and DHA (from oily fish and algae). Most UK adults get too little EPA and DHA.
If you eat oily fish twice a week, food usually covers you. If you don’t, an EPA/DHA supplement from fish or algal oil is the cleanest fix. Flaxseed and plant oils help in a smaller way because the body only converts a tiny fraction of ALA into EPA and DHA.
This guide explains what omega-3 actually does, how much you need, where to get it in the UK, and who should supplement.
What omega-3 actually is
Omega-3s are long-chain polyunsaturated fatty acids. They’re “essential” because your body can’t build them from scratch. You have to eat them.
There are three forms worth knowing:
- ALA (alpha-linolenic acid): the plant form. Found in flaxseed, chia, walnuts, hemp and rapeseed oil.
- EPA (eicosapentaenoic acid): the marine form. Found in oily fish and algae.
- DHA (docosahexaenoic acid): the other marine form. Also from oily fish and algae.
Your body can convert a little ALA into EPA and DHA, but the rate is low. Harvard’s nutrition department estimates under 10% for EPA and under 1% for DHA in most adults. That’s why nutrition guidance leans heavily on oily fish and algae rather than plant sources when the goal is EPA and DHA specifically.
What omega-3 does in the body (the authorised claims)
Under GB health claim rules (the retained EU Nutrition and Health Claims Register), a short list of specific omega-3 statements is authorised. These are the ones with enough evidence to be allowed on labels and in marketing:
- EPA and DHA contribute to the normal function of the heart, at 250 mg combined per day.
- DHA contributes to the maintenance of normal brain function, at 250 mg per day.
- DHA contributes to the maintenance of normal vision, at 250 mg per day.
- Maternal intake of DHA contributes to the normal development of the brain and eye of the foetus and breastfed infants, at 200 mg DHA per day on top of the usual adult omega-3 intake.
- ALA contributes to the maintenance of normal blood cholesterol levels, at 2 g per day.
Beyond the authorised claims, a wider body of research links omega-3 intake with mood, inflammatory markers, joint comfort, sleep quality, and aspects of skin health. DHA is a structural component of skin cell membranes, and EPA plays a role in how the skin responds to UV and inflammatory triggers. The specific effects on outcomes like acne or skin ageing are still mixed in the research and aren’t covered by authorised health claims. Anything you read saying omega-3 “treats” or “cures” a condition is overstating the evidence.
How much omega-3 you need
There’s no single number every authority agrees on, but the UK-relevant guidance is consistent:
- NHS: at least one portion of oily fish per week (around 140 g cooked).
- EFSA: 250 mg combined EPA and DHA per day for general adult health.
- Pregnancy and breastfeeding: an extra 100–200 mg DHA per day on top of usual intake.
The EFSA considers intakes of up to 5 g combined EPA and DHA per day tolerable for adults. The US FDA’s equivalent guideline is 3 g per day from supplements. Both are well above what most UK adults actually eat.
For ALA, the UK Scientific Advisory Committee on Nutrition suggests 0.2% of daily energy intake, which works out at roughly 1.5–2 g per day for most adults.
The best UK food sources
Food first is the sensible starting point for most people. Oily fish is the highest-density dietary source of EPA and DHA.
| Food | Approx EPA + DHA per 100 g | Notes |
|---|---|---|
| Mackerel (Atlantic) | ~2,500 mg | One of the richest UK-available sources |
| Salmon (farmed) | ~2,000 mg | Levels depend on feed; wild and farmed differ |
| Sardines (tinned) | ~1,500 mg | Cheap, long shelf life, low mercury |
| Herring | ~1,700 mg | Similar profile to mackerel |
| Anchovies (tinned) | ~1,300 mg | Small, low mercury |
| Tuna (fresh) | ~1,000 mg | Higher mercury; NHS limits fresh tuna to 4 portions a week for most adults |
| Algal oil (supplement) | Varies, check label | Vegan direct source of EPA/DHA |
| Flaxseed / chia / walnuts | High in ALA only | Useful, but low ALA to EPA/DHA conversion |
| Fortified foods (omega-3 eggs, some milks and yoghurts) | ~50–100 mg per serving | Useful top-up; check the label, as amounts vary widely |
One 140 g portion of mackerel or salmon a week is enough to hit the 250 mg EPA/DHA target as a weekly average. Sardines on toast twice a week lands you comfortably in range. Tinned mackerel and sardines are also the cheapest reliable UK sources, often under £1 a tin in major supermarkets.
UK supermarkets now stock omega-3-enriched eggs and some fortified milks and yoghurts. The per-serving amount is small compared to oily fish, but these add up usefully if you eat them regularly.
Vegan and vegetarian options
If you don’t eat fish, the practical route is algal oil. Algae is where fish get their EPA and DHA from in the first place, so algal oil gives you the same active fats without the fish intermediary.
Plant sources like flaxseed, chia, walnuts and hemp give you ALA. They’re useful for overall intake and for meeting the ALA cholesterol-maintenance claim at 2 g per day, but they’re not a substitute for EPA and DHA. If you’re vegan and want to hit the 250 mg EPA/DHA mark, algal oil is the reliable way.
A quick note on plant oils and cooking: flaxseed and chia oils are heat-sensitive and oxidise quickly when heated, which damages the ALA and produces off-flavours. Use them cold on salads, in smoothies, or stirred into cooked food after heating. For actual cooking, stick to olive oil or rapeseed oil, both of which have a moderate ALA content and are stable at normal cooking temperatures.
Who actually needs an omega-3 supplement
Most UK adults eating oily fish once or twice a week don’t need one. Supplementation makes sense if any of the following apply:
- You don’t eat fish, or eat it less than once a week
- You’re vegan or vegetarian
- You’re pregnant or breastfeeding and want to reliably hit the DHA recommendation
- Your GP or a registered dietitian has specifically recommended it
If you eat oily fish most weeks, the honest answer is that a capsule adds little. Food covers you.
What to look for on a supplement label
Omega-3 supplements are a crowded and inconsistent category. The label tells you most of what you need to know if you read it properly.
- EPA and DHA in mg per serving. Not “total omega-3”. ALA can pad the headline number without doing much.
- Source. Algal oil is the cleanest vegan option. Fish oil should name the species and carry sustainability credentials (MSC, Friend of the Sea, or equivalent).
- Freshness. Oxidised fish oil can cause digestive side effects and loses activity. A TOTOX value below 26 and a recent manufacturing date are good signs.
- Third-party testing. IFOS, Informed Sport or similar independent testing for purity and heavy metals.
- No gelatine if you’re vegan. Many “fish oil” capsules use bovine or porcine gelatine shells.
Supplement form affects how well the fats are absorbed. Natural triglyceride and re-esterified triglyceride fish oils absorb better than the cheaper ethyl ester form, by roughly 30–70% in comparison studies. Liquid fish and algal oils and standard softgel capsules both work well when freshness is good. Gummies are usually a weak choice because the EPA/DHA dose per gummy tends to be much lower than labels imply. Whichever form you choose, the label should name the form and specify EPA and DHA in milligrams per serving.
Side effects and interactions
Omega-3 is well tolerated at normal doses. At higher doses you might notice:
- Fishy aftertaste or burps (less common with enteric-coated and fresh products)
- Mild digestive upset
- Increased bleeding time at very high intakes
Speak to your GP or pharmacist before starting a supplement if you take any of the following:
- Anticoagulants or antiplatelet medication (warfarin, apixaban, clopidogrel, aspirin)
- Blood pressure medication
- Diabetes medication
- Cholesterol-lowering medication
Most clinicians advise stopping omega-3 supplements 1 to 2 weeks before planned surgery because of the mild effect on bleeding time.
Mercury and fish safety in the UK
Mercury gets brought up a lot in omega-3 discussions. The NHS and Food Standards Agency guidance is clear: for most adults, the benefits of eating oily fish outweigh the mercury risk, and smaller species carry less mercury than large predatory ones.
Practical rules for the UK context:
- Pregnant and breastfeeding women: no more than two portions of oily fish a week, and avoid shark, marlin and swordfish.
- Most other adults: up to four portions of oily fish a week is within guidance.
- Small oily fish (sardines, anchovies, mackerel, herring) are consistently lower in mercury than large ones.
A decent fish oil supplement is molecularly distilled, which removes heavy metals below detectable limits. A reputable algal oil has none to begin with.
Omega-3 in pregnancy
DHA contributes to the normal brain and eye development of the foetus and breastfed infants when the mother’s daily intake is at least 200 mg DHA on top of her regular omega-3 intake. That is an authorised claim under GB health claim rules.
In practice, that means pregnant and breastfeeding women are often advised to either eat two portions of oily fish a week (within the NHS safety limits above) or take a DHA-containing supplement. Fish oil, algal oil, and some prenatal multivitamins contain DHA in that range.
Discuss any new supplement with your midwife or GP before starting.
Omega-3 vs omega 3-6-9 supplements
Combined 3-6-9 supplements are a popular but largely redundant category. Most UK diets already contain plenty of omega-6. Adding more from a capsule is the opposite of what most people need.
If you were going to choose between a pure omega-3 supplement and a 3-6-9 blend, the straightforward omega-3 is usually the better choice. We’ve written a full breakdown of the category in our guide on omega 3 6 9 supplements and whether you actually need all three.
The omega-3 to omega-6 ratio
Total omega-3 intake is only half the story. The ratio of omega-6 to omega-3 in the UK diet sits around 15:1 on average, much higher than the 1:1 to 4:1 range most nutrition researchers recommend. The imbalance is associated with higher markers of background inflammation in the blood.
Closing the gap is more about reducing refined seed oils and processed foods than about loading up on fish oil. For a deeper look at how the ratio works and which UK food swaps move it most, see our guide on the omega 3 to omega 6 ratio.
Complementary nutrients worth knowing about
Omega-3 sits alongside a small group of nutrients that UK adults are commonly low on. None of these replace omega-3, but they’re worth looking at if your underlying goal is long-term cardiovascular and immune health.
Vitamin D3 with K2 is the common first add. Most UK adults are low on vitamin D between October and March because UK sunlight is too weak for the skin to produce enough. D3 contributes to the normal function of the immune system and the maintenance of normal bones and teeth, and K2 supports the way calcium is directed to bone rather than soft tissue.
NAC (N-acetyl cysteine) is a precursor to glutathione, the body’s main internal antioxidant. Glutathione supports the pathways that manage oxidative stress. Our guide on boosting glutathione naturally covers this in more detail.
Neither is a substitute for adequate omega-3 intake. They work on different pathways.
Our verdict
Omega-3 is genuinely essential and most UK adults are genuinely short on EPA and DHA. The cleanest fix is also the most obvious one: eat oily fish once or twice a week.
If fish isn’t in your diet, a well-made fish oil or algal oil supplement at 250–500 mg combined EPA and DHA a day is a sensible default. Pregnant and breastfeeding women should prioritise DHA specifically, within NHS safety limits.
Skip the 3-6-9 combos. Skip the supplements that only list “total omega-3”. And don’t believe the articles that claim omega-3 treats or cures specific conditions. It’s a foundational nutrient, not a cure.
Frequently asked questions
Is omega-3 a vitamin?
No. Omega-3 is a family of essential fatty acids, not a vitamin. Your body can’t produce them, so they have to come from food or a supplement, which is why they’re called “essential”.
How much omega-3 per day is safe?
EFSA considers combined EPA and DHA intakes up to 5 g per day tolerable for adults. The US FDA’s equivalent guideline is 3 g per day from supplements. Both are well above the 250 mg per day most authorities recommend for general adult health.
How long does omega-3 take to work?
Red blood cell omega-3 levels change over roughly 3 to 4 months of consistent daily intake. That’s how long it typically takes to see meaningful change in blood markers.
Is algal oil as good as fish oil?
Yes, for most purposes. Algae is where fish get EPA and DHA from in the first place. Algal oil supplements typically provide both fatty acids in comparable concentrations and are the sensible vegan choice.
Can I take omega-3 every day?
Yes, daily intake within recommended ranges is the intended way to take it. Check interactions with any prescription medication first.
Does flaxseed oil cover your omega-3 needs?
Only partly. Flaxseed oil is high in ALA, and ALA contributes to normal blood cholesterol at 2 g per day. But the body converts very little ALA into EPA and DHA, so flaxseed on its own is a weak choice for hitting the heart, brain and vision targets.
Is farmed salmon a good omega-3 source?
Yes, although the amount varies with feed. UK farmed salmon typically provides around 2,000 mg EPA and DHA per 100 g portion, which is enough to cover a weekly EPA/DHA target in a single meal.
References
- GB Nutrition and Health Claims Register (retained EU Regulation 1924/2006). Authorised health claims for EPA, DHA and ALA.
- NHS. Fish and shellfish nutrition.
- Harvard T.H. Chan School of Public Health. Omega-3 Fats: An Essential Contribution.
- Simopoulos, A.P. (2002). The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomedicine & Pharmacotherapy.
- Calder, P.C. (2012). Mechanisms of action of (n-3) fatty acids. British Journal of Nutrition.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Tolerable upper intake level of EPA, DHA and DPA.
This article is for general education and isn’t medical advice. If you take prescription medication, have a chronic condition, or are pregnant or breastfeeding, speak to your GP, midwife or a registered pharmacist before starting any new supplement.
