The benefits of fish oil: what omega-3 research really shows

What is fish oil?

Fish oil is oil taken from oily fish, and its value lies in two long-chain omega-3 fats called EPA and DHA.

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are found mainly in oily fish such as salmon, mackerel, sardines, herring and trout. Plant foods such as walnuts and flaxseed provide a different omega-3 called ALA. Oily fish, or a fish oil supplement, is the usual way to get EPA and DHA.

Our omega-3 ingredient guide covers the basics, and the plant form is in our flaxseed oil guide.

What are the proven benefits of fish oil?

EPA and DHA have authorised health claims for the heart, brain, vision, blood pressure and blood fats, each with a minimum daily intake.

These claims are listed on the Great Britain nutrition and health claims register. They are the only benefits a supplement can lawfully state, and each comes with conditions.

Authorised claim	Nutrient	Daily intake needed for the effect
Contributes to the normal function of the heart	EPA and DHA	250 mg
Contributes to maintenance of normal brain function	DHA	250 mg
Contributes to maintenance of normal vision	DHA	250 mg
Contributes to maintenance of normal blood triglyceride levels	EPA and DHA	2 g
Contributes to maintenance of normal blood pressure	EPA and DHA	3 g

Two points matter here. First, the effect depends on the amount of EPA and DHA, not the total amount of fish oil, so always check the label for those two figures. Second, the higher intakes for triglycerides and blood pressure come with a safety note: your total daily intake of EPA and DHA from supplements should not go above 5 g.

Does fish oil prevent heart disease?

The best current evidence suggests fish oil supplements have little or no effect on heart attacks, strokes or overall deaths.

A 2020 Cochrane review pooled large numbers of trials on omega-3 fats. It found that increasing EPA and DHA had little or no effect on deaths from any cause or on cardiovascular events. It found a possible small reduction in coronary heart disease deaths and events, but with low-certainty evidence, and a reduction in triglycerides.

In line with this, the National Institute for Health and Care Excellence (NICE) tells doctors not to offer omega-3 fatty acid compounds to prevent cardiovascular disease, with one prescription-only exception. Instead, NICE advises people at risk to eat at least two portions of fish a week, including one portion of oily fish.

So fish oil contributes to normal heart function, which is different from preventing heart disease. If you have a heart condition or high cholesterol, follow your doctor's plan and do not use a supplement in place of prescribed treatment.

Is it better to eat oily fish or take fish oil?

Eating fish comes first; a supplement is a backup for people who rarely eat it.

The NHS recommends at least two portions of fish a week, one of which should be oily. A portion is about 140 g. Oily fish also gives you protein, vitamin D and other nutrients that a capsule does not.

There are upper limits for oily fish because of pollutants it can contain:

• Girls and women who are pregnant, breastfeeding or may become pregnant: no more than 2 portions of oily fish a week.
• Other adults: no more than 4 portions a week.

A fish oil supplement can make sense if you do not eat fish, or eat it rarely. Vegetarians and vegans can get ALA from walnuts, flaxseeds, chia seeds, rapeseed oil and soya foods, or look at algae-based omega-3.

How much fish oil should you take?

Look for a supplement that provides at least 250 mg of EPA and DHA combined each day.

That is the intake linked to the heart, brain and vision claims. Higher intakes, such as 2 g or 3 g a day, are the amounts linked to the triglyceride and blood pressure claims. The European Food Safety Authority concluded that supplemental intakes of combined EPA and DHA up to about 5 g a day do not raise safety concerns for adults. That is a safety ceiling, not a target.

Fish oil or fish liver oil?

They are not the same. The British Dietetic Association advises choosing an omega-3 fish oil rather than fish liver oil, such as cod liver oil. Fish liver oil contains vitamin A, and supplements containing vitamin A should be avoided if you are pregnant or planning a pregnancy.

Who should take care with fish oil?

Most adults tolerate fish oil well, but some people should speak to a professional first.

• If you take blood thinners such as warfarin, or antiplatelet medicines, speak to your GP or pharmacist before taking fish oil, especially at higher doses, as omega-3 can affect blood clotting.
• If you are pregnant or planning a pregnancy, avoid fish liver oil and check any supplement with your midwife or GP.
• If you have a fish allergy, avoid fish oil and ask about algae-based options.

Where fish oil fits in your routine

For most people, the simplest approach is oily fish once a week, and a quality omega-3 supplement if that is not realistic.

If you are looking after your heart more broadly, our heart collection brings together our heart-focused formulas. Cholestilite includes flaxseed oil alongside plant sterols and garlic, and our Coenzyme Q10 provides CoQ10, which is central to energy production in heart and muscle cells. If you take any regular medicine, check with your pharmacist before adding something new.