Fish Oil

Fish oil is oil extracted from fish such as cod, herring, mackerel, tuna, salmon, anchovy and sardine. In the United States it is one of the most commonly used dietary supplements other than vitamins and minerals; it serves as a source of the long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Fish do not make these acids themselves: they are made by microalgae at the base of the marine food chain, and fish take them in through the food chain and store them in their tissues.

As a supplement

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. Cod liver oil also gives vitamin A and vitamin D. Fish oil supplements have not been found to contain the methylmercury that occurs in seafood, because it is removed during processing.

In fish oil, omega-3s occur naturally as triglycerides; some supplements contain ethyl esters made from them, which the body takes up somewhat less well, although all forms clearly raise EPA and DHA levels in the blood.

Safety

Side effects are usually mild: an unpleasant taste, bad breath, heartburn, nausea, digestive discomfort, diarrhoea, headache and smelly sweat. Fish oil can interact with warfarin and similar blood thinners. Most research, however, shows that 3 to 6 g of fish oil a day does not significantly change the effect of warfarin.

Products containing it

• Omega 3 Forte fish and krill oil capsules (D 237)
• Salmon oil capsules, Vital Plus (S 04)