Nitric oxide, often shortened to NO, is a naturally produced signalling molecule involved in blood flow, vascular tone, oxygen delivery, skeletal muscle function and exercise physiology [1,2].
One of its best-known roles is vasodilation, meaning it helps blood vessels relax and widen. This supports more efficient circulation and may help deliver oxygen and nutrients to working tissues during physical activity [1,2].
NO3, NO2 and NO: what is the difference?
The dietary nitrate pathway is often written as:
NO3 → NO2 → NO
NO3 is nitrate. It is found naturally in foods such as beetroot, spinach, rocket, lettuce and celery. Dietary nitrate can act as a reservoir for nitric oxide production [1,2].
NO2 is nitrite. After nitrate is consumed, the body can convert some of it into nitrite through microbial and physiological pathways. Nitrite is an important intermediate between nitrate and nitric oxide [1].
NO is nitric oxide. Nitrite can be further converted into nitric oxide, especially in conditions where oxygen availability is lower or acidity is higher, such as in working muscle during exercise [1,3].
This nitrate-nitrite-nitric oxide pathway is separate from the body’s other main route to NO production, which uses the amino acid L-arginine and nitric oxide synthase enzymes [1].
Why might people want to support nitric oxide?
Nitric oxide is important because it helps regulate blood vessel function and circulation. For active individuals, this is particularly relevant because blood flow, oxygen delivery and muscle efficiency are all linked to exercise performance [1,3].
Dietary nitrate, especially from beetroot, has been studied for its potential to improve exercise efficiency. Research suggests beetroot juice supplementation may reduce the oxygen cost of submaximal exercise and support endurance performance in some settings [3].
The response can vary. Dose, timing, training status, diet and individual physiology all matter. Nitrate is not a stimulant like caffeine. It works through conversion into nitrite and nitric oxide, so its effects are more closely linked to vascular and metabolic pathways [1,3].
Food sources of nitrate
The richest natural sources of nitrate are usually vegetables, particularly beetroot and leafy greens. Beetroot is widely used in sports nutrition research because it is naturally nitrate-rich and can be standardised in juice, powder or extract form [3].
Vegetable-derived nitrate should be viewed differently from nitrate or nitrite used in processed meats. Vegetables provide nitrate alongside vitamin C, polyphenols, fibre and other plant compounds, which changes the nutritional context [2,4].
By contrast, nitrite-cured processed meats contain amine-rich proteins and may be cooked at high temperatures. These conditions can favour the formation of N-nitroso compounds, including nitrosamines, some of which are considered genotoxic and carcinogenic [4,5].
This does not mean nitrate-rich vegetables should be avoided. The concern is mainly around nitrite-cured processed meats and the conditions that can promote nitrosamine formation [4,5].
L-arginine and L-citrulline
Nitric oxide can also be produced from L-arginine. This is the classical nitric oxide synthase pathway and is one reason L-arginine is commonly associated with nitric oxide support [1,6].
L-citrulline is also relevant because it can be converted into L-arginine in the body. Research suggests L-citrulline may raise plasma L-arginine effectively, partly because it bypasses some first-pass metabolism [6].
Some studies have also examined L-citrulline and L-arginine together, with evidence that the combination may increase plasma L-arginine and nitric oxide bioavailability more effectively than either amino acid alone in certain settings [7].
Nitric oxide and exercise performance
Interest in nitric oxide is particularly strong in sports nutrition. During exercise, working muscles need oxygen and nutrients, while also clearing metabolic by-products. Nitric oxide is involved in vascular signalling, blood flow and muscle function, all of which are relevant to performance [1,3].
Beetroot juice studies suggest that nitrate may improve efficiency during endurance exercise by helping the body perform a given workload with slightly less oxygen demand [3].
Final thoughts
Nitric oxide is central to blood flow, vascular signalling and exercise physiology. Dietary nitrate provides one route to NO through the nitrate-nitrite-NO pathway, while L-arginine and L-citrulline support the body’s amino acid-dependent route.
For most people, the foundation is a varied diet rich in nitrate-containing vegetables, regular exercise and good overall cardiovascular health. Beetroot and leafy greens remain some of the most relevant dietary sources for those interested in naturally supporting nitric oxide pathways.
[4] Food Standards Agency. “Nitrates and Nitrites: The Science Explained.”
