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Understanding Nitric Oxide and Blood Vessel Function
Nitric oxide is one of those molecules that appears frequently in health headlines. It's genuinely important in the body — but it's also the subject of plenty of marketing. This guide separates the well-established science from the less certain claims.
What nitric oxide does
Nitric oxide (NO) is a small signalling molecule. In blood vessels, it is produced by the endothelium — the thin layer of cells lining the inside of arteries. It signals the surrounding smooth muscle to relax, which allows vessels to widen. This is part of how the body adjusts blood flow to meet changing needs, such as during exercise.
The discovery of nitric oxide's role as a signalling molecule in the cardiovascular system was recognised with the Nobel Prize in Physiology or Medicine in 1998.
How the body makes it
There are two main routes. The first uses enzymes called nitric oxide synthases, which make NO from the amino acid L-arginine. The second is the nitrate–nitrite–nitric oxide pathway, in which nitrate from foods — especially leafy greens and beetroot — is converted, partly with the help of bacteria in the mouth, into nitrite and then nitric oxide.
How lifestyle relates to vascular health
Research suggests that regular physical activity supports healthy endothelial function, while factors such as smoking, high blood pressure and physical inactivity are associated with poorer blood vessel health. This is one reason why the everyday habits recommended by the NHS and British Heart Foundation — moving more, eating plenty of vegetables, not smoking — matter so much.
What about supplements?
Many supplements are marketed as 'nitric oxide boosters', often containing ingredients such as beetroot extract, L-citrulline or L-arginine. Some studies have looked at dietary nitrate (for example, beetroot juice) and blood pressure or exercise performance, with mixed results that vary depending on the person and the study design.
It's important to be clear about what is not established: there is no good evidence that most healthy people need to raise their nitric oxide levels, and supplements are not a substitute for prescribed treatment or a healthy lifestyle. Some ingredients may interact with medicines, particularly those for blood pressure, erectile dysfunction or angina (nitrates).
Sources
- Förstermann U, Sessa WC. Nitric oxide synthases: regulation and function. European Heart Journal, 2012.
- Lundberg JO, Weitzberg E, Gladwin MT. The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics. Nature Reviews Drug Discovery, 2008.
- British Heart Foundation — Healthy living
This article is for general information only and is not medical advice. See our health disclaimer.