Dietary Nitrates and Physical Performance: an Umbrella Meta-Analysis

How do nitrates travel from the plate to the muscle?

The journey from dietary nitrates to physiological effect involves several biochemical steps. Nitrates (NO3−) from leafy vegetables — rocket, spinach — or from concentrated beetroot juice are absorbed in the intestine and then partially concentrated in saliva. Oral bacteria reduce NO3− to nitrite (NO2−); the swallowed nitrite enters the bloodstream and in tissues — especially under the low-pH and hypoxic conditions characteristic of working muscle — is further reduced to nitric oxide (NO).

NO is a short-lived signalling gas with two key effects on physical performance:

• Vasodilation: vessel dilation improves delivery of oxygen and substrates to muscles.
• Mitochondrial efficiency: NO reduces the oxygen cost of work by increasing the efficiency of mitochondrial oxidative phosphorylation and accelerating phosphocreatine resynthesis after intense effort.

The result: for the same mechanical output (watts, speed), oxygen consumption decreases. This is what makes nitrates an ergogenic tool — not a central nervous system stimulant.

What did the 2025 umbrella meta-analysis find?

Poon et al. (Sports Medicine, 2025) synthesised 20 systematic reviews with meta-analyses, covering 180 unique primary studies and 2,672 participants. This is an umbrella meta-analysis — the highest level of the evidence hierarchy, synthesising already-completed meta-analyses.

Confirmed significant effects of nitrate loading:

• Muscular endurance: SMD 0.48 (95% CI 0.23–0.74) — the most pronounced of all outcomes.
• Time to exhaustion (TTE): SMD 0.33 (95% CI 0.19–0.47) — a reliable moderate effect.
• Peak power: SMD 0.25 (95% CI 0.10–0.39).
• Total distance covered: SMD 0.42 (95% CI 0.09–0.76).

Absence of significant effects:

• Time trial (fixed distance): SMD -0.03 (p=0.65) — no improvement.
• VO2max: no significant effect (p=0.20).
• Mean power: no significant improvement.

Endurance vs. time-trial performance: what is the difference?

The discrepancy between a significant effect on TTE and no effect on time trials is important to understand. Time to exhaustion (TTE) is a fixed-intensity protocol: the subject works at a given power or speed until complete exhaustion. A time trial involves covering a fixed distance in the shortest possible time.

The difference is physiological: in TTE the key factor is the ability to sustain effort under increasing acidosis; in a time trial the athlete self-selects their pace and can compensate for the metabolic advantage of nitrates through tactical decisions. In addition, time trials have greater result variability, which statistically makes it harder to detect moderate effects.

In practical terms this means: nitrates are more beneficial for training and fixed-intensity loading protocols than for competitive distance events.

Who benefits more from nitrates and why?

The umbrella meta-analysis identifies a pattern: untrained and recreationally active individuals experience a more pronounced effect from nitrate loading than highly trained athletes. The authors attribute this to a ceiling effect: in well-trained athletes the cardiovascular system, mitochondrial network, and buffering systems are already highly optimised, narrowing the scope for additional improvement.

In untrained individuals the baseline level of NO signalling and vascular efficiency is lower — nitrates are in a more advantageous position here. This makes nitrate loading particularly relevant for people of intermediate fitness levels, not only for athletes.

Additional context: some data suggest greater nitrate efficacy under hypoxic conditions (e.g., altitude training) or in a state of fatigue — that is, precisely where mitochondrial efficiency is most impaired.

Dosage and practical nitrate sources

According to the umbrella meta-analysis by Poon et al. (2025), the minimum effective dose is 6 mmol of nitrates per day, corresponding to approximately 372 mg of nitrates. Chronic supplementation lasting more than 3 days produces a more pronounced effect on time to exhaustion than a single pre-exercise dose. For muscular endurance, however, significant effects were observed regardless of protocol duration.

Main dietary sources with high nitrate content:

• Rocket (arugula): approximately 480 mg of nitrates per 100 g — one of the richest sources.
• Beetroot and beetroot juice: 150–250 mg per 100 g; concentrated beetroot juice (70 ml) typically contains about 6.4 mmol of nitrates.
• Spinach: 150–250 mg per 100 g.
• Lettuce, celery, radish: moderate content.

An important caveat: the use of antibacterial mouthwashes suppresses nitrate-reducing salivary bacteria and blocks the NO3− → NO2− conversion, which according to several studies nullifies the ergogenic effect. If you are using nitrates as a supplement, avoid antiseptic mouthwashes during this period.