Not laughing gas, not smog
Three similar names often get mixed up:
| Name | Formula | What it is |
|---|---|---|
| Nitric oxide | NO | The signaling molecule this guide is about. The body makes small amounts and breaks it down within seconds. |
| Nitrous oxide | N₂O | “Laughing gas,” used by dentists and as a whipped-cream propellant. |
| Nitrogen dioxide | NO₂ | A brown air pollutant from traffic and burning fuel. |
A molecule that won a Nobel Prize
In 1980 Robert Furchgott showed that blood vessels relax only when their inner lining, the endothelium, is intact. The lining was releasing an unknown signal. Louis Ignarro and others later identified that signal as nitric oxide, and Ferid Murad had already shown that nitroglycerin works by releasing nitric oxide. The three shared the 1998 Nobel Prize in Physiology or Medicine. The journal Science had named nitric oxide its “Molecule of the Year” in 1992.
There is a twist of history here. Nitroglycerin is the explosive behind Alfred Nobel's dynamite fortune, which funds the Nobel Prizes. Late in life Nobel had heart trouble, and his doctors prescribed nitroglycerin. A century later the prize carrying his name went to the scientists who explained how that medicine works.
What nitric oxide does
Nitric oxide made in the endothelium moves into the muscle layer of the vessel wall and switches on an enzyme called soluble guanylate cyclase. The muscle relaxes and the vessel widens. The signal lasts only seconds, so the body keeps making it. Nerve cells and immune cells also use nitric oxide, each for different jobs.
Researchers often check this system with flow-mediated dilation (FMD): an ultrasound scan of the arm artery after a blood-pressure cuff is released. The more the artery widens, the more strongly the endothelium responded. FMD is a research marker, not a test people use at home.
Two ways the body makes nitric oxide
| Pathway | Raw material | What it needs |
|---|---|---|
| Enzyme (NOS) pathway | L-arginine, which becomes NO and L-citrulline | Nitric oxide synthase enzymes, oxygen and the cofactor BH4 |
| Nitrate–nitrite–NO pathway | Nitrate from food, mainly leafy greens and beetroot | Bacteria on the tongue that turn nitrate into nitrite; no NOS enzyme |
The two routes complement each other. The food route works better where oxygen is low, exactly where the enzyme route slows down. Because mouth bacteria do one of the steps, a 2013 study found that a week of antibacterial mouthwash lowered nitrite in saliva and blood in healthy volunteers. The nitrate-rich foods guide covers the food side.
Why “just take more arginine” is not the whole story
The main enzyme in blood vessels should already have plenty of arginine at normal blood levels. Yet in some studies extra arginine still raised nitric oxide. Researchers call this the L-arginine paradox. A leading explanation is ADMA, a molecule the body makes that blocks the enzyme. What matters is the balance between arginine and ADMA, not arginine alone.
Form matters too. Much oral arginine is broken down in the gut and liver. In one study in healthy volunteers, oral L-citrulline raised blood arginine more effectively than L-arginine itself.
Made versus lost
Nitric oxide can also be lost before it acts. Under oxidative stress, or when BH4 runs short, the enzyme can make superoxide, a free radical, instead of nitric oxide. Superoxide also reacts with nitric oxide extremely fast, forming peroxynitrite. A simple way to picture it: nitric oxide available = nitric oxide made − nitric oxide lost. This is established biochemistry. It does not show that any particular food or supplement changes nitric oxide in people.
How to read nitric oxide marketing
- Look for what a product contains: arginine or citrulline (enzyme route), nitrate (food route), or plant extracts with antioxidant compounds (the “loss” side).
- Ask whether a claim comes from a human study with a control group, an animal study or a test tube. The guide to reading supplement research explains the difference.
- Testimonials and “increase” percentages from saliva strips are not evidence that a product does anything for your health.
- If you take blood pressure medicine, nitrates for chest pain or medicines for erectile dysfunction, talk to your clinician before using any product marketed for nitric oxide.
Sources and further reading
- The Nobel Prize in Physiology or Medicine 1998 (NobelPrize.org)
- Celermajer et al.: Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis (Lancet, 1992)
- Lundberg, Weitzberg & Gladwin: The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics (Nat Rev Drug Discov, 2008)
- Kapil et al.: Physiological role for nitrate-reducing oral bacteria in blood pressure control (Free Radic Biol Med, 2013)
- Bode-Böger, Scalera & Ignarro: The L-arginine paradox: importance of the L-arginine/ADMA ratio (Pharmacol Ther, 2007)
- Schwedhelm et al.: Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine (Br J Clin Pharmacol, 2008)
- Förstermann & Münzel: Endothelial nitric oxide synthase in vascular disease: from marvel to menace (Circulation, 2006)
- Pacher, Beckman & Liaudet: Nitric oxide and peroxynitrite in health and disease (Physiol Rev, 2007)
Sources provide context and limitations; they do not turn a general education page into medical advice.
Quick answers
Is nitric oxide the same as nitrous oxide?
No. Nitric oxide (NO) is a signaling molecule the body makes. Nitrous oxide (N₂O) is laughing gas, used as an anesthetic and as a propellant.
Who discovered nitric oxide as a signal?
Robert Furchgott, Louis Ignarro and Ferid Murad shared the 1998 Nobel Prize in Physiology or Medicine for discoveries about nitric oxide as a signaling molecule in the cardiovascular system.
Which foods are linked to nitric oxide?
Vegetables rich in nitrate, such as arugula, spinach, lettuce, beetroot and celery, feed the nitrate–nitrite–nitric oxide pathway. Protein foods supply L-arginine for the enzyme pathway.
Can a supplement raise my nitric oxide?
Some ingredients act on one of the two pathways, but effects differ between people and products. A product label or a testimonial does not show an effect on your health. Ask your clinician, especially if you take heart or blood pressure medicines.