Nitric oxide (NO) is a tiny gaseous signaling molecule with which the inner lining of the vessels, the endothelium, tells the smooth muscle of the wall to relax. The result is dilation of the vessel and increased blood flow.
The discovery of NO's role as a signaling molecule of the cardiovascular system was awarded the Nobel Prize in 1998. NO lives for seconds, but it largely determines vascular tone and blood-pressure level.
How NO is produced
The endothelium produces NO from the amino acid L-arginine with the help of the enzyme endothelial NO synthase (eNOS), oxygen and NADPH. One stimulus, in particular, is "shear stress" — the friction of flowing blood against the wall — which is why regular physical activity boosts NO production.
Once released, NO penetrates the smooth-muscle cells and triggers their relaxation — vasodilation.
NO, the endothelium and aging
With age, and with smoking, hypertension, diabetes and high cholesterol, NO production falls while oxidative stress destroys it. This state — endothelial dysfunction — is the earliest stage of atherosclerosis, before any plaques appear.
A decline in NO raises blood pressure and reduces vascular elasticity — the vessels "age" faster than one's calendar age.
How it is measured and maintained
NO is hard to measure directly because of its short life, so its action is assessed indirectly — by flow-mediated dilation (FMD): on ultrasound one sees how much an artery widens after a brief occlusion. Good endothelial function is supported by exercise, a Mediterranean diet, nitrate-rich vegetables (beetroot, greens), quitting smoking and control of blood pressure and cholesterol.
Calculate using this marker
Calculators where Nitric oxide (NO) is used directly:
Frequently asked questions
How can I naturally raise nitric oxide?
Regular aerobic exercise works best: blood flow stimulates NO production by the endothelium. Nitrate-rich vegetables (beetroot, spinach, arugula), quitting smoking and blood-pressure control help. L-arginine supplements give a limited and inconsistent effect.
Is nitric oxide linked to blood pressure?
Directly. NO dilates vessels and lowers blood pressure; when its production falls (endothelial dysfunction), vessels are narrowed and stiff and pressure rises. That is why NO deficiency is an early mechanism of hypertension and atherosclerosis.