Arginine is a conditionally essential amino acid, depending on the developmental stage and health status of the individual. Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because it is a component of all protein-containing foods and can be synthesized in the body from glutamine via citrulline.
Arginine is the immediate precursor of NO, an important signaling molecule which can act as a second messenger, as well as an intercellular messenger which regulates vasodilation, and also has functions in the immune system's reaction to infection. Arginine is also a precursor for urea, ornithine, and agmatine; is necessary for the synthesis of creatine; and can also be used for the synthesis of polyamines.
* Amino acids which are essential amino acids which cannot be made by the human body and, therefore, must be obtained in the diet.
Tillery, Enger and Ross