The amino acid arginine gained popularity as a bodybuilding supplement, but research shows it may be best for one muscle in particular: the heart. Cells use arginine to make nitric oxide, which helps keep blood vessels healthy. It's found in plant foods, dairy products, nuts, chocolate, fish and meats.
Uses: Arginine supplements are taken to prevent and treat heart disease, erectile dysfunction and male infertility and to increase lean muscle mass and improve exercise performance. The amino acid is injected to treat human growth hormone deficiency.
Dose: Most people get 3 to 5 grams a day from their diets. Supplemental doses range from 5 grams (for erectile dysfunction) up to 20 grams (for exercise, preventing heart disease and increasing sperm production). Supplements come in pill and powder form.
Precautions: Some doctors caution that arginine supplements could trigger herpes outbreaks in people infected with the virus. Taking more than 30 grams a day can cause cramps and diarrhea. Little is known about the supplement's long-term safety.
Research: In lab and animal studies, arginine shows promise for treating heart disease by preventing blood from clotting; keeping blood vessels from hardening and constricting; and keeping levels of LDL, or "bad" cholesterol, low. The amino acid also boosts immune cell function in lab and animal tests, in some cases reducing the risk of tumor development. In human studies, the amino acid has shown promise in treating people with high blood pressure, high cholesterol and chest pain caused by decreased blood flow to the heart. In other human trials, arginine supplements increased sperm count in infertile men and helped treat erectile dysfunction, but more studies will be needed to confirm its effects. Evidence is inconclusive about its effectiveness at reducing body fat and improving performance.-- Elena Conis