If you eat oily fish once or twice a week, you probably don’t need an omega-3 capsule. Supplements make sense in specific situations: when you hardly ever eat fish, during pregnancy if your diet falls short, or when a doctor prescribes them to lower triglycerides. In healthy people, the large clinical trials have not shown that taking them prevents heart problems.
What omega-3 is and why there is so much talk about it
These are fatty acids the body needs but cannot make in sufficient amounts. There are three main types:
- ALA (alpha-linolenic acid): comes from plant sources such as flaxseed, chia, walnuts and some oils (flaxseed, soya, rapeseed).
- EPA (eicosapentaenoic acid): found in fish and seafood.
- DHA (docosahexaenoic acid): also in fish and seafood; it is an important component of the brain and the retina.
The body can convert some ALA into EPA and DHA, but that conversion is limited. That is why recommendations and supplements usually talk about EPA and DHA, the two that come from fish (and from some algae).
How much you need
The authorities don’t set the same figure for every type:
| Body | What it recommends |
|---|---|
| European Food Safety Authority (EFSA) | 250 mg a day of EPA and DHA combined as an adequate intake to maintain heart health in healthy adults |
| US National Institutes of Health (NIH) | Adequate intake of ALA: 1.6 g a day for men and 1.1 g for adult women (1.4 g in pregnancy) |
| EFSA and FDA (safety limit) | Up to 5 g a day of EPA and DHA combined in supplements raises no safety concerns in adults |
To give you an idea: 85 g (about 3 ounces) of farmed salmon provides around 1.2 g of DHA and 0.6 g of EPA, according to NIH data. A single portion of oily fish comfortably exceeds the 250 mg a day when spread across the week.
Where to get it without capsules
- Oily fish: salmon, mackerel, sardines, herring, tuna.
- Seeds and nuts: flaxseed, chia and walnuts (provide ALA).
- Fortified foods: some eggs, yoghurts or milks have added omega-3.
- Algal oil: a source of DHA suitable for vegans.
What the studies say
Heart. Eating one or two portions of fish a week is associated with a lower cardiovascular risk. With capsules the picture is less clear: the VITAL trial, with more than 25,000 healthy adults, found no significant reduction in major cardiovascular events overall.
Triglycerides. This is the best-established effect. At high doses, omega-3s lower triglycerides. For very high levels there are prescription medicines (American Heart Association guidance mentions 4 g a day). That is not the same as a capsule from a health shop: the dose and medical monitoring are different.
Eyes. A diet rich in omega-3 is linked to a lower risk of age-related macular degeneration, but supplements have not been shown to slow its progress.
Brain and mood. The results are mixed and more studies are needed. There is no solid basis for taking omega-3 in the hope of improving memory.
Pregnancy. DHA plays a role in the baby’s development. The NIH mentions that eating 230 to 340 g of fish a week may benefit fetal development. It is worth discussing with your midwife or doctor, especially regarding which fish you can eat.
When supplementing may make sense
- You don’t eat fish because you don’t like it, can’t tolerate it or follow a vegan diet (in that case, look at algal oil capsules).
- Your doctor has prescribed omega-3 for high triglycerides or for another reason.
- You are pregnant or breastfeeding and your diet doesn’t include fish, always after checking with a professional.
How to choose a supplement
- Look at the EPA and DHA content, not the total “fish oil”. A 1,000 mg fish oil capsule usually provides only about 180 mg of EPA and 120 mg of DHA.
- Compare the amount per daily dose, not per capsule.
- Choose brands with quality control and a clear expiry date; the oil oxidises over time.
- Don’t overdo the dose. More is not better: in trials in people with cardiovascular disease or high risk, 4 g a day of omega-3 slightly increased the risk of atrial fibrillation.
Side effects and interactions
They are usually mild: an unpleasant taste, bad breath, heartburn, nausea, digestive discomfort, diarrhoea, headache and body odour. Taking the capsule with a meal helps you tolerate them.
High doses can increase the risk of bleeding when combined with warfarin or other anticoagulants. If you take any, ask before starting. And if you are allergic to fish or shellfish, check the source of the supplement carefully.
When to see a doctor
- You take anticoagulants or antiplatelet drugs and want to start omega-3.
- You have heart disease, palpitations or arrhythmias.
- You have been found to have high triglycerides or cholesterol and are thinking of treating yourself.
- You notice unusual bleeding (gums, nose, bruises) after starting the supplement.
- You have an allergic reaction: hives, swollen lips or difficulty breathing (emergency).
- You are pregnant, breastfeeding or plan to give it to a child.
This article is for information only and does not replace advice from a healthcare professional. Sources: NIH, Office of Dietary Supplements: Omega-3 (consumers), NIH, Omega-3 (health professionals) and EFSA: safety of long-chain omega-3 fatty acids.