What Is Nitric Oxide? A Practical Guide to Its Role in the Body
Nitric oxide is a short-lived signaling molecule made throughout the body. In blood vessels, it plays an important role in normal vascular signaling and smooth-muscle relaxation.
What nitric oxide does
Endothelial cells can produce nitric oxide, which diffuses locally and participates in signaling that influences vascular tone. Nitric oxide also has roles outside the cardiovascular system, including neural and immune signaling.
Two pathways worth knowing
One major route uses L-arginine and nitric oxide synthase. Another involves dietary nitrate, which can be reduced to nitrite and then contribute to nitric-oxide formation under certain physiological conditions. These are related but distinct routes.
Why supplements use the term
Most “nitric oxide supplements” contain precursors or dietary ingredients connected to these pathways rather than nitric oxide itself. Common examples include beetroot, L-citrulline and L-arginine.
What nitric oxide does not mean
The phrase should not be used as shorthand for treating vascular disease. Normal physiology, exercise effects and disease treatment are separate questions with different standards of evidence.
Where to go next
Read how the body makes nitric oxide for the mechanisms, or our supplement guide if you are evaluating products.