What are omega-3 fatty acids?
Omega-3s are a family of polyunsaturated fats that your body needs but cannot make in useful amounts, so they have to come from food. There are three main types [1]:
- ALA (alpha-linolenic acid), the most common omega-3 in most diets. It comes mainly from plant oils, nuts and seeds.
- EPA (eicosapentaenoic acid), a long-chain omega-3 found mainly in fish and seafood. The body uses it to make signalling molecules called eicosanoids, which are involved in inflammation [6].
- DHA (docosahexaenoic acid), the other long-chain omega-3 from fish and seafood. It is a structural part of cell membranes and is especially concentrated in the brain and the retina of the eye [1].
Your body can turn some ALA into EPA and DHA, but only in very small amounts [1]. That is why eating fish, or for vegetarians and vegans an algae-based source, is the practical way to get the long-chain forms. The Well Aliments infographic above also names several lesser-known omega-3s, such as stearidonic acid (SDA) and docosapentaenoic acid (DPA), which are present in food in much smaller amounts.
Omega-3 benefits and what the evidence shows
People who eat fish and seafood regularly have a lower risk of several long-term diseases, but researchers cannot always tell whether that comes from the omega-3s or from eating those foods in general [1]. For several conditions the evidence for eating fish is stronger than for taking supplements [2]. Here is where the main claimed benefits stand.
Heart health
This is the best supported benefit. Eating oily fish as part of a healthy diet helps protect against some heart problems, and higher intakes of EPA and DHA lower triglycerides, a type of fat in the blood [1]. A 2020 review of 86 studies found that extra EPA and DHA slightly reduced the risk of coronary events and coronary death [2]. The American Heart Association recommends about 1 g a day of EPA plus DHA for people with heart disease, preferably from oily fish, but does not recommend supplements for people who are not at high risk [1].
Brain development in pregnancy and early life
DHA is needed to build the brain and nervous system from the third trimester of pregnancy into the second year of life [3]. The NHS says long-chain omega-3 can help a baby’s nervous system develop [4]. Taking supplements in pregnancy, however, has not been shown to change a child’s long-term development [2].
Eye health
The evidence is mixed. People who eat more omega-3s may have a lower risk of age-related macular degeneration, but supplements do not slow the disease once it has started, and a year-long trial found fish oil worked no better than a placebo for dry eye [1].
Inflammation and joint pain
Some trials suggest that people with rheumatoid arthritis who take omega-3 supplements alongside their usual treatment may need fewer painkillers, but it is not clear whether pain or stiffness actually improve [1].
Mood and depression
Uncertain. A 2021 review of 35 studies found that any effect of omega-3s on depression may be too small to matter [2].
Cancer
Not supported for supplements. A large clinical trial found that omega-3 supplements did not lower overall cancer risk or the risk of breast, prostate or colorectal cancer [1]. The infographic’s claim that omega-3 reduces the risk of certain cancers goes further than this evidence.
How much omega-3 do you need?
There is no official recommended amount for EPA and DHA. The only official intake figures are for ALA: 1.6 g a day for men and 1.1 g for women, rising to 1.4 g in pregnancy and 1.3 g when breastfeeding, with lower amounts for children [1].
The infographic suggests at least 250 to 500 mg of combined EPA and DHA a day for healthy adults, 200 mg of DHA in pregnancy and 50 to 100 mg for children. These figures are the maker’s, not official recommendations in the US or UK sources we checked [1].
In the UK the NHS gives the advice in fish rather than milligrams: eat at least 2 portions of fish a week, one of them oily, with a portion about 140 g [4]. In pregnancy it advises no more than 2 portions of oily fish a week, because oily fish can contain pollutants such as mercury [5].
The best food sources of omega-3
Oily fish are the richest source of EPA and DHA. The NHS lists herring, pilchards, salmon, sardines, sprats, trout and mackerel [4]. The infographic also lists canned light tuna, but the NHS says fresh and canned tuna do not count as oily fish, so it is a weaker choice [4].
Plant foods supply ALA: flaxseed (linseed) and flaxseed oil, chia seeds, walnuts, and soybean and canola (rapeseed) oils [1]. Because so little ALA is converted, vegetarians and vegans who want EPA and DHA can use algal oil supplements, a vegetarian source made from algae [1].
Omega-3 side effects and interactions
Side effects from omega-3 supplements are usually mild. The NIH lists an unpleasant taste, bad breath, heartburn, nausea, stomach discomfort, diarrhoea, headache and smelly sweat [1]. The infographic adds burping, joint pain and vomiting; joint pain and vomiting are not on the NIH list. The US Food and Drug Administration advises taking no more than 5 g a day of EPA and DHA combined from supplements [1].
The more important risk is with other medicines. High doses of omega-3s may cause bleeding problems when taken with warfarin or other blood thinners [1]. Speak to your GP or pharmacist before taking supplements if you take any regular medication, are pregnant, or have a bleeding disorder.
Omega-3 from food or supplements?
For most people, food is the better route. The strongest benefits in the research come from eating fish, and oily fish is also a good source of vitamin D, while some canned fish with edible bones adds calcium [1][4]. Supplements may help people who do not eat fish, and the American Heart Association says people with heart disease can use them under the guidance of a health professional [1]. If you do take a supplement, check how much EPA and DHA it contains per capsule rather than the total fish oil, as the two figures can be very different.
Questions about omega-3 benefits
What does omega-3 do for the body?
Omega-3s are part of the membranes around every cell, with DHA especially concentrated in the brain and eyes, and they have roles in the heart, blood vessels, lungs, immune system and hormone-producing glands [1]. Eating enough is linked to better heart health and supports a baby’s brain development in pregnancy [1][4].
How much fish oil should I take per day?
There is no official daily target for healthy adults. The American Heart Association suggests about 1 g a day of EPA plus DHA for people with heart disease [1]. In the UK the NHS recommends eating oily fish once a week rather than a set dose [4]. Ask a doctor or pharmacist before taking more than a standard supplement.
What happens if you take omega-3 every day?
For most healthy adults a standard daily supplement is safe, with possible mild side effects such as a fishy taste, heartburn or an upset stomach [1]. High doses can increase the risk of bleeding, especially with blood thinners [1].
What should you not mix omega-3 with?
The NIH warns that high doses of omega-3s may cause bleeding problems when taken with warfarin or other anticoagulant medicines, and advises talking to a health professional about interactions [1].
What is the difference between EPA and DHA?
Both are long-chain omega-3s from fish. DHA is mainly structural, forming part of the brain, retina and sperm cells, while EPA is used to make signalling molecules called eicosanoids, which are involved in inflammation [1].
Sources
- NIH Office of Dietary Supplements, Omega-3 Fatty Acids, Fact Sheet for Consumers.
- NIH National Center for Complementary and Integrative Health, Omega-3 Supplements, What You Need To Know.
- Harvard T.H. Chan School of Public Health, The Nutrition Source, Omega-3 Fatty Acids.
- NHS, Fish and shellfish.
- NHS, Foods to avoid in pregnancy.
- Well Aliments, wellaliments.com, the maker of the infographic (a supplement company).
This page is general information, not medical advice.
Last reviewed 2 November 2026
