The black currant shrub is native to Europe and parts of Asia and is particularly popular in Eastern Europe and Russia. Traditional herbalists uphold that black currant has diuretic (increases urine flow), diaphoretic (promotes sweating), and antipyretic (fever reducer) properties. In Europe, it has been used topically (applied to the skin) to treat skin disorders, such as atopic dermatitis, and as part of gargles to treat sore throats. Black currant juice has been boiled down into a sugary extract, called Rob, to treat sore throat inflammation, colds, the flu, and febrile (fever) illness. A mixture made from black currant bark has been used to treat calculus (hardened plaque), edema (swelling), and hemorrhoids. With a vitamin C content estimated to be five times that of oranges (2,000 milligrams/kilogram), black currant has potential dietary benefits. Black currant is also rich in rutin and other flavonoids, which are known antioxidants. Because of black currant's high essential fatty acid content, researchers believe that it may be effective in the treatment of inflammatory conditions and pain management, as well as in regulating the circulatory system and increasing immunity. As a medicinal treatment, black currant seed oil is the most commonly used part of the plant and is available in capsule form. The effectiveness of black currant seed oil is mixed and safety concerns seem to be minor in non-allergic people.
Dietary sources of omega-3 fatty acids include fish oil and certain plant/nut oils. Fish oil contains both docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), while some nuts (e.g., English walnuts) and vegetable oils (e.g., canola, soybean, flaxseed/linseed, and olive oil) contain alpha-linolenic acid (ALA). Evidence from several studies has suggested that amounts of DHA and EPA in the form of fish or fish oil supplements lowers triglycerides, slows the buildup of atherosclerotic plaques ("hardening of the arteries"), lowers blood pressure slightly, as well as reduces the risk of death, heart attack, dangerous abnormal heart rhythms, and strokes in people with known heart disease. However, high doses may have harmful effects, such as an increased risk of bleeding. Although similar benefits are proposed for alpha-linolenic acid, scientific evidence is less compelling, and beneficial effects may be less pronounced. Some species of fish carry a higher risk of environmental contamination, such as with methylmercury.