Oral ingestion of L-citrulline from watermelon increases plasma L-arginine concentrations by bypassing hepatic metabolism and enabling renal conversion to L-arginine, which enhances nitric oxide synthesis and improves vascular function in adults with cardiovascular risk factors.

When L-citrulline from watermelon is eaten, it skips the liver and goes straight to the kidneys, where it is turned into L-arginine. This L-arginine enters the bloodstream and reaches blood vessel walls, where it is used to make nitric oxide. Nitric oxide tells the muscle around blood vessels to relax, making the vessels wider and lowering blood pressure. At the same time, compounds in watermelon reduce harmful molecules that would otherwise destroy nitric oxide or stop it from working properly.