Two pathways to nitric oxide
Your body makes NO through two main routes.
The first is the enzymatic pathway: endothelial cells lining blood vessel walls use an enzyme called nitric oxide synthase (eNOS) to convert the amino acid L-arginine directly into NO. This process runs continuously and depends on cofactors including zinc and adequate blood flow — physical activity upregulates it through mechanical shear stress on vessel walls.
The second route, described comprehensively in 2008, is the nitrate-nitrite-NO pathway [1]. Dietary nitrate (NO₃⁻), found abundantly in leafy greens and beetroot, is absorbed in the small intestine and then actively concentrated in saliva at up to ten times blood levels. Bacteria living on the tongue and back of the throat reduce salivary nitrate to nitrite (NO₂⁻), which the body then converts to NO — particularly in low-oxygen environments like exercising muscle and ischemic tissue. This pathway is independent of eNOS and can compensate when the enzymatic route is impaired.
What nitric oxide does in the body
Blood pressure regulation. When endothelial cells release NO into the artery wall, it diffuses into surrounding smooth muscle and triggers relaxation, widening the vessel. Lower resistance means lower blood pressure without extra cardiac effort. A human trial found that a single serving of beetroot juice (~500 mL, 22.5 mmol nitrate) reduced systolic blood pressure by 10.4 mmHg and diastolic by 8.1 mmHg within three hours, with effects lasting 24 hours — a reduction correlated directly with peak plasma nitrite levels [2].
Platelet inhibition. NO prevents platelets from sticking together unnecessarily. The same beetroot juice intervention significantly reduced ex vivo platelet aggregation in response to collagen and ADP [2], suggesting a direct anticoagulant-like effect through dietary means alone.
Exercise efficiency. NO dilates blood vessels in working muscle and regulates mitochondrial respiration, improving the efficiency of ATP production per unit of oxygen consumed. Multiple studies show dietary nitrate reduces whole-body oxygen cost during submaximal exercise by 3–5% — the same effort feels meaningfully easier [4]. This effect appears most pronounced in recreational exercisers rather than elite athletes.
Supporting NO through diet
The richest dietary sources of nitrate:
- Rocket (arugula) — ~490 mg per 100 g
- Beetroot — ~250 mg per 100 g
- Spinach — ~250 mg per 100 g
- Radishes — ~215 mg per 100 g
- Celery — ~200 mg per 100 g
- Lettuce — ~150 mg per 100 g
L-arginine and L-citrulline feed the enzymatic pathway separately. See our L-Arginine page and L-Citrulline page for detail on those pathways. The Beets page covers beetroot's performance applications specifically.
A practical note on mouthwash: antibacterial mouthwash kills the tongue bacteria that convert nitrate to nitrite, blocking the dietary pathway entirely. Studies confirm that rinsing with mouthwash before exercise eliminates the blood-pressure and performance benefits of beetroot juice. This is one reason many researchers now question routine antibacterial mouthwash use.
Who benefits most
Evidence is strongest in healthy adults and those with elevated blood pressure. Results in established type 2 diabetes are mixed — one well-designed trial found no blood pressure improvement despite raised plasma nitrite levels, possibly because impaired eNOS activity downstream limits the response [5]. Older adults and those with compromised endothelial function may have reduced enzymatic NO production but can still benefit from the dietary nitrate route.
Evidence Review
Mechanistic foundation
Lundberg, Weitzberg, and Gladwin's 2008 review in Nature Reviews Drug Discovery established the modern framework for the nitrate-nitrite-NO pathway [1]. They described how nitrate — long dismissed as an inert end product of NO metabolism — is actively recycled into vasoactive NO via salivary microbiota, with biological effects particularly pronounced in hypoxic and ischemic tissue. This reframing of a dietary component as a conditionally essential vascular nutrient drove the subsequent decade of human trial work.
Cardiovascular RCT evidence
Webb et al. (2008) conducted a double-blind crossover trial in 14 healthy adults comparing single-dose beetroot juice (500 mL, ~22.5 mmol NO₃⁻) against nitrate-depleted control juice [2]. Primary outcomes: systolic BP −10.4 mmHg (p<0.01) and diastolic BP −8.1 mmHg (p<0.01) at peak effect (approximately 3 hours), sustained at 24 hours. Platelet aggregation was significantly reduced. The study established that dietary nitrate has rapid, clinically meaningful cardiovascular effects through the salivary pathway.
Bondonno, Croft, and Hodgson (2016) reviewed the broader clinical trial evidence [3], confirming consistent improvements across: resting blood pressure (across multiple RCTs), endothelial function measured by flow-mediated dilation, ischemia-reperfusion injury outcomes, arterial stiffness, and platelet aggregation. The review concluded that dietary nitrate from vegetables likely contributes meaningfully to the cardiovascular protection associated with Mediterranean and DASH diets.
Exercise physiology evidence
Jones et al. (2021) synthesized exercise physiology research on dietary NO₃⁻ [4]. Key findings: the 3–5% reduction in oxygen cost during moderate exercise is robustly replicated across labs; the effect at the muscle level involves improved coupling of oxygen consumption to ATP production within mitochondria; skeletal muscle itself stores nitrate and can serve as a local reservoir for NO generation during hypoxic bursts. Timing matters: the nitrate-to-nitrite conversion by oral bacteria takes several hours, so beetroot juice or nitrate supplements are most effective when consumed 2–3 hours before exercise. Dose thresholds: effects typically emerge at 5–8 mmol nitrate, equivalent to approximately 300–500 mL concentrated beetroot juice. Evidence in elite-level athletes is weaker, possibly due to higher baseline NO capacity from sustained training.
Limitations
Gilchrist et al. (2013) tested 7.5 mmol dietary nitrate daily for two weeks in 27 adults with type 2 diabetes in a double-blind crossover design [5]. Despite significantly raised plasma nitrite, no improvements were seen in blood pressure, flow-mediated dilation, or insulin sensitivity. The result highlights an important caveat: impaired eNOS function and downstream signaling in metabolic disease may limit the response to increased NO substrate. The study was underpowered (n=27) and may not rule out smaller effects, but it tempers expectations for dietary nitrate as a standalone intervention in T2D.
Overall, the evidence for dietary nitrate supporting NO-mediated cardiovascular protection in healthy and pre-hypertensive individuals is mechanistically well-understood and replicated across multiple independent RCTs. Effect sizes are clinically meaningful and comparable to lifestyle interventions. Evidence strength is moderate-to-high for blood pressure and exercise efficiency outcomes in healthy populations.