Docosahexaenoic acid (DHA) is an omega-3 oil found primarily in cold-water fish such as salmon, mackerel, sardines, herring, cod, tuna, and anchovies. The oil belongs to a class of nutrients known as essential fatty acids, which are fats that are required for normal biological functions but cannot be manufactured in the body, and therefore must be included in the diet. While purified DHA is available as an individual supplement, the oil is most commonly found in the form of fish oil capsules, which contain high concentrations of DHA and another omega-3 essential fatty acid, EPA (eicosapentaenoic acid). Cod liver is also a rich source of DHA and EPA, along with the fat-soluble vitamins A and D.
Dosage recommendations for DHA vary widely with intended application and form used. A common recommendation for fish oil (typically 2 parts DHA to 3 parts EPA) is 3 grams per day, in divided doses. For high triglycerides, studies indicate that isolated DHA may be effective at an intake of 1.25 grams per day. DHA has very low toxicity and appears to be well tolerated at this dosage range. High intakes of fish oil may cause an unpleasant "fishy burp" in some cases.