arginine

Arginine, or L-arginine, is a semi-essential amino acid that is among the 20 standard amino acids used to build proteins. It has the chemical formula C6H14N4O2 and a molecular weight of about 174.2 g/mol. At physiological pH its side chain carries a guanidinium group, giving arginine a basic character.

In humans, arginine is produced mainly through the urea cycle in the liver and is also formed from ornithine. It is hydrolyzed by arginase to yield ornithine and urea, a key step in nitrogen excretion. Arginine is also a precursor for several important metabolites, including nitric oxide via nitric oxide synthase, agmatine, polyamines, and proline. While the body can synthesize arginine, certain conditions such as infancy, severe illness, and injury may make dietary intake more important.

Physiological roles of arginine include involvement in protein synthesis, wound healing, and immune function. Its most notable function is as a precursor to nitric oxide, a signaling molecule that promotes vasodilation and regulates blood flow. Through other pathways, arginine contributes to creatine synthesis and polyamine production, which are important for cell proliferation and tissue maintenance.

Dietary sources of arginine include lean meats, fish, dairy products, eggs, and plant foods such as seeds, nuts, legumes, and whole grains. There is no official Recommended Dietary Allowance for arginine, but adequate protein intake generally supports its availability for the body's needs.

Arginine is available as an oral supplement and is popular for cardiovascular health, erectile function, and athletic performance. Evidence for these uses is mixed. High doses can cause gastrointestinal upset and may interact with medications that lower blood pressure or with nitrates. Some individuals with recurrent herpes infections may be advised to avoid arginine, as it can potentially promote viral replication; consult a clinician before use.