Fish Oil: Who Might Consider It and What to Check

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Fish oil is a concentrated source of the long-chain omega-3 fats EPA and DHA, which oily fish such as salmon, mackerel, sardines and trout provide naturally. It mainly makes sense for adults who rarely eat oily fish, and before you buy any capsule it is worth checking how much EPA and DHA it actually supplies, how fresh the oil is, whether you have a fish allergy and whether you take any medicines that affect blood clotting.

Below you will find who tends to fall short, how to read a fish oil label, which safety questions matter and what the authorised claims for EPA and DHA really say.

What is fish oil and how is it different from omega-3?

Omega-3 is a family of fats rather than a single substance. Alpha-linolenic acid (ALA) comes from plant foods such as walnuts, flaxseed and rapeseed oil, while eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) come mainly from fish and seafood. The body converts only a small share of ALA into EPA and DHA, which is why oily fish matters so much in dietary advice. Our guide to omega-3 and your diet covers the whole family in more detail.

Fish oil is simply oil extracted from fatty fish and then refined, usually into capsules or a liquid. Mayo Clinic describes it as a dietary source of omega-3 fatty acids and notes that refined fish oil appears to contain almost no mercury, which is one reason some people prefer it to eating large amounts of certain fish.

Who might consider taking fish oil?

UK healthy-eating advice suggests eating at least two portions of fish a week, one of which should be oily. Many households manage the white fish on a Friday but rarely buy mackerel or sardines, and some people simply dislike the taste. If that sounds like your week, you are the person a fish oil supplement is designed for.

Vegetarians and vegans are in a different position, because fish oil does not fit their diet at all; for them, algae oil is the usual alternative, which we explain in our article on vegetarian omega-3.

If you already eat oily fish once or twice a week, a supplement is unlikely to add much. Mayo Clinic says people who eat fish at least twice a week have a lower risk of dying from heart disease, while fish oil supplements appear to offer little to no heart benefit, so the food itself remains the better habit.

How much EPA and DHA do adults need?

EFSA, the European Food Safety Authority, set an adequate intake of 250 mg of EPA and DHA combined per day for healthy adults. In the same 2012 opinion it found that average intakes among European adults are around 400 to 500 mg a day from food, although that average hides many people who eat almost no fish at all.

The table below shows roughly where different eating habits leave you. It is a guide to your situation rather than a precise calculation.

Your typical week	Likely EPA and DHA picture	What to think about
Two fish meals, one of them oily	Usually comfortably above 250 mg a day on average	A supplement is rarely needed.
White fish only, such as cod or haddock	Lower, because white fish contains much less fat	Try adding one oily fish meal, or consider a supplement.
Fish once a month or less	Often well below 250 mg a day	A daily fish oil capsule is a reasonable back-up.
Vegetarian or vegan	Very little EPA and DHA from food	Look at algae oil rather than fish oil.

What should you check on a fish oil label?

The front of a pack often shows a large figure such as 1,000 mg. That number usually refers to the weight of the whole oil in a capsule, not to the omega-3 content. Turn the pack over and look for the nutrition table, where EPA and DHA should be listed separately and for the full daily dose.

It also helps to note how many capsules make up that daily dose. A product that seems strong per capsule may need three or four capsules a day, while another needs just one. Divide the EPA and DHA total by the number of capsules and you can compare products fairly. Our explainer on what NRV means on a supplement label covers the rest of the table.

Freshness is the next point. Fish oil is a polyunsaturated fat, and it oxidises when exposed to heat, light and air. A strong rancid smell when you open the pot can be a sign of an old or poorly stored product, so keep the pot closed and away from heat and sunlight.

Is fish oil safe for everyone?

For most healthy adults, fish oil taken as directed is considered safe. EFSA concluded that supplemental intakes of EPA and DHA combined of up to 5 g a day do not raise safety concerns for adults, which is far above what a normal supplement provides. Mayo Clinic lists mild side effects such as a fishy aftertaste, bad breath, heartburn, nausea and loose stools, and notes that high doses may increase the risk of bleeding.

A few situations call for a conversation with a GP or pharmacist before you start:

• You take an anticoagulant or antiplatelet medicine, or another supplement that affects blood clotting.
• You take medicine for blood pressure, because fish oil may lower blood pressure slightly.
• You have a fish or shellfish allergy, since it is unclear whether fish oil is safe for people with a seafood allergy.
• You are due to have surgery, are pregnant or are breastfeeding.

Pregnant women are often unsure about fish. Mercury limits apply to certain fish in pregnancy, but cod liver oil is a separate concern because it contains vitamin A, which is generally avoided in pregnancy. A midwife or GP can tell you which option suits you.

What can fish oil actually claim to do?

Food supplements sold in the UK and the EU may only use health claims that have been authorised and listed in the official register, and only if the product contains enough of the nutrient. For EPA and DHA the authorised claim reads: EPA and DHA contribute to the normal function of the heart. The beneficial effect is obtained with a daily intake of 250 mg of EPA and DHA.

For DHA alone there are two authorised claims, each needing 250 mg of DHA a day: DHA contributes to maintenance of normal brain function, and DHA contributes to the maintenance of normal vision. Anything beyond these wordings, such as promises about joints, mood or memory, is not an authorised claim. Our article on why supplements can only say certain things explains how the system works.

Which fish oil supplement do we use?

If you have decided that a supplement fits your diet, look for one that states its EPA and DHA content clearly. The LR Super Omega capsules provide 630 mg of EPA and 420 mg of DHA in the daily dose of three capsules, which is 1,050 mg of EPA and DHA combined. With that amount, EPA and DHA contribute to the normal function of the heart, DHA contributes to maintenance of normal brain function, and DHA contributes to the maintenance of normal vision. The capsules are made with fish oil, so they are not suitable for vegetarians or for anyone with a fish allergy, and it is worth reading the full ingredient list before ordering. You can see the other options in our daily supplements category.

Here is the product we mention in this article:

When should you see a doctor?

A supplement is not the place to start if you have symptoms. Speak to your GP if you have chest pain, breathlessness, palpitations or swelling in your ankles, if you have been told your blood fats or blood pressure are high, or if you notice unusual bruising or bleeding after starting fish oil. Call 999 for chest pain that spreads to your arm, jaw or back. Always tell your doctor or pharmacist which supplements you take, because they may matter when new medicines are prescribed.

Frequently asked questions

Is cod liver oil the same as fish oil?

Cod liver oil comes from the liver of the cod and contains vitamins A and D as well as omega-3. Ordinary fish oil comes from the body of oily fish and usually has no added vitamin A. The difference matters in pregnancy and if you already take other supplements with vitamin A.

When is the best time to take fish oil?

Many people take it with a meal, because the fat in food can make the capsules easier on the stomach and may reduce fishy burps. The time of day itself matters less than taking it regularly. Follow the dose printed on the label.

Can I take fish oil alongside other supplements?

Usually yes, but read the labels so that you do not double up on the same nutrients, especially vitamins A and D. If you take any prescribed medicines, ask your pharmacist to check the combination.

Do I still need to eat fish if I take a supplement?

Oily fish brings protein, vitamin D, selenium and iodine as well as omega-3, so a capsule does not replace it. If you can manage one portion a week, it is still worth doing.

Sources

• EFSA: EFSA assesses safety of long-chain omega-3 fatty acids
• Mayo Clinic: Fish oil
• European Commission: EU Register of nutrition and health claims

Food supplements are not medicines and do not replace a varied, balanced diet and a healthy lifestyle. This article is general information and not medical advice; if you have a health condition, take medication or are pregnant, speak to your GP or pharmacist first.