Dietary nitrate / beetroot and endurance performance
Jones 2014 review + McMahon 2016 meta-analysis
Key Findings (evidence summary)
Pathway (Jones 2014): inorganic nitrate from green leafy vegetables and beetroot → nitrite (stored and circulated in blood) → in low-oxygen conditions, nitric oxide, which regulates vascular and metabolic control
Physiology (Jones 2014): nitrate supplementation raises plasma nitrite, lowers resting blood pressure, reduces the oxygen cost of submaximal exercise, and "in some circumstances" enhances exercise tolerance and performance
Meta-analysis (McMahon 2016): 47 studies / 76 trials of placebo vs nitrate-only supplementation with a performance measure ≥30 s
Pooled effect: trivial and non-significant in favour of nitrate (ES −0.10, 95% CI −0.27 to 0.06 in the paper's direction convention; p > 0.05)
Time to exhaustion (22 trials): small-to-moderate significant benefit (ES 0.33, 95% CI 0.15-0.50, p < 0.01)
Graded exercise test (8 trials): small, non-significant (ES 0.25, 95% CI −0.06 to 0.56)
Time trial (28 trials): the modality least likely to benefit (authors' conclusion)
No significant heterogeneity; no significant moderators (exercise type, dose duration, nitrate type, study quality, fitness level, % nitrite change)
Dose, timing and food sources: Jones 2014 states that practical guidelines for safe and efficacious supplementation are provided, but the abstract gives no numbers; none are stated here
Practical Application
Superseded on the headline claim: nitrate does NOT improve time-trial performance. The 2025 umbrella review over 20 meta-analyses found no time-trial or VO2max effect (REF-3493); what survives is time to exhaustion, muscular endurance and peak power — consistent with McMahon 2016, where time to exhaustion improved (ES 0.33) and time trials did not.
In 47 studies (76 trials), nitrate supplementation improved time-to-exhaustion tests (ES 0.33) but had a trivial, non-significant pooled effect and was least likely to help time-trial performance — and Jones 2014's core physiological finding is a lower oxygen cost of submaximal exercise. For an athlete that means nitrate may make a fixed submaximal pace cheaper and extend the time it can be held, but it is not a proven race-time improver.
Not from this paper; the base's own practice: dosing by beetroot concentrate a few hours before exercise, with several days of loading, follows the manufacturers' and the wider literature's protocols — this entry's abstracts give no dose, timing or food-source numbers. Test in training first.
Not from this paper; the base's own practice: avoid antibacterial mouthwash around nitrate use — the oral bacteria that reduce nitrate to nitrite are the first step of the pathway Jones describes.
Hypoxia: Jones 2014 notes nitrite → NO conversion is favoured at low oxygen availability; a larger effect at altitude is a plausible inference, not a tested result in these abstracts.
Limitations
Partly superseded (2026-09-02). These are 2014 and 2016 sources. REF-3493 (Poon 2025, umbrella review) finds no effect on time trial or VO2max while confirming time to exhaustion, muscular endurance and peak power. Use THIS entry for mechanism and the McMahon breakdown by test type; use REF-3493 for what nitrate moves.
Fitness level did not moderate the effect in McMahon's meta-regression; the entry's earlier "elite respond less" claim is not supported by these abstracts
Individual response variable (gut/oral microbiome-dependent — see REF-358/SYNTH-08)
Very high chronic doses may interact with medications (nitrates for angina contraindication) — clinical caution, not a finding of these papers
Gut distress possible at high doses; beet colour in urine/stool is cosmetic only
Audit note (2026-07-06)
DOI: 10.1007/s40279-014-0149-y | PMID: 24791915 [DOI CORRECTED 2026-07-09]
Level A/B unchanged (justified by the McMahon meta-analysis).
How this entry was checked and changed
Why this level
(McMahon meta-analysis: 47 studies, 76 trials); the Jones review alone would be B+
Content correction 2026-09-27
"Recreational ES ~0.30, ~2-3% TT improvement; well-trained ES ~0.10-0.20; elite smallest" -> McMahon's abstract: pooled ES −0.10 (n.s.), TTE 0.33, GXT 0.25, TT least likely to benefit, and fitness level was NOT a significant moderator; the tiered-by-training-status claim removed.
"5-9 mmol (300-600 mg) per dose", "O2 cost −3-7%", "2-3 h pre", "3-6 days at 6-8 mmol/day", "~6-8 mmol per 70 mL", "500-600 mg", "5-40 min TTs", "mouthwash 24 h" -> none in either abstract; removed or relabelled as the base's own practice without numbers.
Level "A (recreational) / B (elite)" -> A (meta-analysis), the split by training status having no support. Tier "4-5 Elite" -> mixed. Sport "running" -> general.
2026-09-28: added Journal line from the Europe PMC record (DOI 10.1007/s40279-014-0149-y, PMID 24791915).