Omega-3 fatty acids
Main omega-3s
Several omega-3s exist, but most research is on three: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA has 18 carbon atoms; EPA, with 20, and DHA, with 22, are called long-chain omega-3s.[1]
ALA is an essential fatty acid: the body cannot make it, so it must come from the diet. The body can turn some ALA into EPA and then DHA, but very little, at reported rates of less than 15%, so eating EPA and DHA directly from foods or supplements is the only practical way to raise their levels.[1]
In the body
Omega-3s are parts of the phospholipids that build cell membranes; DHA is especially high in the retina, brain and sperm. Together with omega-6s, omega-3s also provide energy and are used to make eicosanoids, signalling molecules that work in the heart and blood vessels, lungs, immune system and hormone system.[1]
Food and supplements
ALA occurs in plant oils such as flaxseed oil, soybean and canola oil, and in chia seeds and walnuts. EPA and DHA occur in fish, fish oil and krill oil, but they are first made by microalgae at the base of the marine food chain, not by the fish.[1]
Cold-water fatty fish such as salmon, mackerel, tuna, herring and sardines contain large amounts of long-chain omega-3s; leaner fish such as bass, tilapia and cod, and shellfish, contain less.[1]
Supplements with long-chain omega-3s include fish oil, krill oil, cod liver oil and vegetarian products with algal oil. A typical fish oil supplement gives about 1,000 mg of fish oil with 180 mg of EPA and 120 mg of DHA, but doses vary widely. Omega-3 supplements have not been found to contain the methylmercury that occurs in seafood, because it is removed during processing.[1]
How much
In the United States, adequate intakes have been set only for ALA: 1.6 g a day for men and 1.1 g for women, 1.4 g in pregnancy and 1.3 g while breastfeeding. No intake recommendations were set for EPA, DHA or the other long-chain omega-3s.[1]
Too little
A lack of essential fatty acids, omega-3s or omega-6s, can cause rough, scaly skin and dermatitis.[1]
Safety and medicines
Side effects of omega-3 supplements are usually mild: an unpleasant taste, bad breath, heartburn, nausea, digestive discomfort, diarrhoea, headache and smelly sweat.[1]
High doses of EPA and DHA, 2 to 15 g a day, might lengthen bleeding time; according to the European Food Safety Authority, long-term intake of EPA and DHA together at up to about 5 g a day appears to be safe. Fish oil supplements can interact with warfarin and similar blood thinners, although most research shows that 3 to 6 g of fish oil a day does not significantly change the effect of warfarin.[1]
Products containing it
- Omega 3 Forte fish and krill oil capsules (D 237)
- Salmon oil capsules, Vital Plus (S 04)