L-Arginine is a semi-essential amino acid synthesized by the body from ornithine. Arginine supports protein synthesis as it is involved in the transport and storage of nitrogen. Arginine is important for proper physical performance because it is used by the body to produce creatine. L-Arginine promotes muscle-building activity in the body by increasing levels of anabolic (growth-promoting) hormones such as insulin and growth hormone. Arginine is necessary for the execution of many physiological processes. Supplementation with L-arginine has significantly increased the quantity and cytotoxic activity of NK cells and lymphokine-activated cells in patients with breast cancer. Learn more on arginine-health-benefits.