Dietary nitrate supplementation and exercise performance

Abstract

Dietary nitrate supplementation, primarily delivered through beetroot juice, has emerged as a well-characterized ergogenic strategy with consistent evidence of improving exercise efficiency and performance. This review by Jones, Vanhatalo, and Bailey (2018) comprehensively examined the mechanisms, evidence base, and practical applications of nitrate supplementation for exercise performance across a range of athletic populations and exercise modalities.

The nitrate-nitrite-nitric oxide pathway represents the primary mechanism: ingested nitrate is reduced by oral bacteria to nitrite, which is subsequently reduced to nitric oxide in hypoxic tissues during exercise, enhancing mitochondrial efficiency, reducing the oxygen cost of exercise, and improving blood flow to contracting muscles [1]. Meta-analytic evidence supports a meaningful improvement in exercise economy of approximately 2-3%, translating to significant performance gains in time-trial and endurance-dominated activities [2].

The review identified important population moderators: the ergogenic effect is most consistent in recreational to moderately trained athletes, while elite athletes may show attenuated responses, possibly due to habitually higher plasma nitrate levels [3]. A loading protocol of 2-3 days and an acute dose equivalent to 6-8 mmol of nitrate (approximately 500mL of beetroot juice) were identified as optimal for maximizing plasma nitrite availability at the time of exercise.

Keywords: dietary nitrate, beetroot juice, nitric oxide, exercise economy, mitochondrial efficiency, ergogenic, endurance performance

Introduction

Nitric oxide (NO) occupies a central position in exercise physiology as a signaling molecule that regulates vascular tone, mitochondrial respiration, muscle contractile function, and glucose uptake. For decades, researchers recognized NO's importance to exercise capacity, but the primary focus was on endogenous NO synthesis via the L-arginine-eNOS pathway [1]. The discovery that inorganic nitrate in dietary sources could serve as an alternative, oxygen-independent source of NO production fundamentally expanded the nutritional strategies available to athletes seeking to enhance NO bioavailability.

The nitrate-nitrite-NO pathway operates through a series of reduction reactions that become increasingly favored in conditions of low oxygen availability — precisely the tissue environment during intense exercise. Dietary nitrate (NO₃⁻) consumed through food or supplements is absorbed in the small intestine and enters the circulation, where approximately 25% is taken up by salivary glands and secreted into saliva [2]. Commensal bacteria on the tongue reduce salivary nitrate to nitrite (NO₂⁻), which is then swallowed and absorbed. In hypoxic tissues with low pH — conditions that characterize intensely exercising skeletal muscle — nitrite is further reduced to nitric oxide by a variety of reductases including deoxyhemoglobin and xanthine oxidoreductase.

This pathway has several appealing pharmacological characteristics relative to L-arginine supplementation. First, because it produces NO through an oxygen-independent mechanism, it is most active precisely when conventional eNOS activity is most limited (during heavy exercise with tissue hypoxia). Second, dietary nitrate from food sources such as beetroot, spinach, arugula, and celery provides a naturally occurring, unprocessed source that avoids the pharmacokinetic problems associated with amino acid supplements [3].

Jones and colleagues at the University of Exeter were among the first to systematically characterize the exercise performance effects of beetroot juice supplementation, demonstrating in a landmark 2009 study that 500mL of beetroot juice for 6 days reduced the oxygen cost of submaximal exercise by approximately 5% and increased time to exhaustion [4]. Subsequent work from their group and others expanded the understanding of optimal dosing, timing, population responsiveness, and the specific exercise modalities that benefit most from nitrate supplementation.

<h2>Evidence Review</h2> <h3>Mechanism: From Nitrate to Nitric Oxide</h3> <p>The ergogenic effects of dietary nitrate are attributed to a cascade of biochemical events:</p> <ol> <li><strong>Nitrate absorption</strong>: Ingested NO₃⁻ is absorbed in the proximal small intestine and enters circulation within 30-60 minutes</li> <li><strong>Salivary concentration and bacterial reduction</strong>: ~25% of plasma nitrate is actively concentrated in saliva; oral bacteria (principally <em>Veillonella</em> and <em>Actinomyces</em> species) reduce nitrate to nitrite within 1-2 hours of ingestion</li> <li><strong>Tissue hypoxia-dependent conversion</strong>: During exercise, nitrite accumulates in hypoxic muscle tissue where it is converted to NO by deoxyhemoglobin and other reductases</li> <li><strong>Physiological effects</strong>: NO produced by this pathway inhibits cytochrome c oxidase (reducing mitochondrial oxygen requirements), activates guanylate cyclase (causing vasodilation), and modulates calcium sensitivity of contractile proteins [1]</li> </ol> <p>The oxygen cost reduction — reduced VO₂ at any given exercise intensity — is the most consistently measured physiological outcome and the primary mechanism by which nitrate improves endurance performance [2].</p> <h3>Endurance Exercise Performance</h3> <p>Meta-analyses of randomized crossover trials found that nitrate supplementation improved time-trial performance by approximately 3% and reduced oxygen cost of submaximal exercise by 2-5% [3]. These effects have been replicated across cycling, running, rowing, and swimming, with cycling studies providing the largest body of evidence due to measurement precision advantages.</p> <p>The performance improvement is most pronounced at moderate exercise intensities (60-80% VO₂max) where mitochondrial efficiency gains translate most directly to time-trial performance. At near-maximal intensities, the oxygen-limiting step shifts from mitochondrial efficiency to cardiovascular oxygen delivery, reducing the marginal benefit of mitochondrial efficiency improvements.</p> <h3>Resistance Exercise Applications</h3> <p>Evidence for nitrate supplementation in resistance exercise has expanded beyond endurance sport. Studies examining high-repetition resistance exercise found: - Improved muscular endurance (more repetitions to failure at given <a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>">% 1RM</a>) - Increased blood flow to exercising muscles - Reduced oxygen cost per unit of force produced</p> <p>Coggan et al. demonstrated improved maximal knee extensor power in older adults following acute nitrate supplementation, attributed to enhanced <a href="/terms/type-ii-muscle-fiber/" class="term-link" data-slug="type-ii-muscle-fiber" title="type II <a href="/terms/muscle-fiber/" class="term-link" data-slug="muscle-fiber" title="muscle fiber">muscle fiber</a>">type II muscle fiber</a> contractile efficiency [4].</p> <h3><a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="Dose-Response">Dose-Response</a> and Timing</h3> <table> <thead> <tr> <th>Protocol</th> <th>Plasma Nitrite Peak</th> <th>Performance Effect</th> </tr> </thead> <tbody> <tr> <td>Single dose, 2h before</td> <td>Moderate</td> <td>Acute benefit</td> </tr> <tr> <td>3-day loading</td> <td>Higher, sustained</td> <td>Enhanced benefit</td> </tr> <tr> <td>7-14 day chronic</td> <td>Highest</td> <td>Maximal benefit</td> </tr> </tbody> </table> <p>The 2-3 hour pre-exercise window allows sufficient time for the oral bacteria to convert nitrate to nitrite, with plasma nitrite (and hence NO availability) peaking at this timepoint [5]. A loading period of 2-3 days further elevates tissue nitrite stores, providing greater NO availability at the onset of intense exercise.</p> <h3>Elite Athlete Response</h3> <p>A consistent finding across studies is the attenuated ergogenic response in highly trained athletes. Several proposed explanations include:</p> <ul> <li>Elite athletes already have superior microvascular density and oxygen delivery systems, reducing the marginal benefit of NO-mediated vasodilation</li> <li>Higher habitual vegetable intake in elite athletes may produce chronically elevated baseline nitrate/nitrite concentrations, leaving less room for supplementation to produce additional elevation [6]</li> <li>Enhanced skeletal muscle mitochondrial efficiency in highly trained athletes leaves less room for the mitochondrial efficiency gains that drive nitrate's benefits in less trained populations</li> </ul>

Discussion

Contextualizing the 2-3% Performance Improvement

A 2-3% improvement in time-trial performance may appear modest in absolute terms, but within the context of competitive athletics, this magnitude of improvement can represent the difference between medal and non-medal outcomes. In Olympic-distance triathlon events lasting 1-2 hours, a 2% improvement in run-bike-swim performance represents minutes of time advantage [1]. Even for recreational athletes, improved exercise economy translates to either faster performance at the same subjective effort, or equivalent performance at lower physiological cost — a meaningful quality-of-life improvement for regular exercisers.

The mechanism of economy improvement — reduced oxygen cost at given exercise intensities — represents a qualitatively different performance enhancement than most ergogenic compounds. Rather than stimulating greater energy production, nitrate makes the same amount of energy production more metabolically efficient. This fundamental mechanism has parallels with altitude acclimatization and heat adaptation, both of which improve exercise economy through related NO-dependent vascular and mitochondrial adaptations [2].

Antifungal Mouthwash: An Unexpected Confounder

An important and somewhat unexpected practical finding in the nitrate literature is that antibacterial mouthwash can completely abolish the ergogenic effects of nitrate supplementation. By eliminating the oral bacteria responsible for nitrate-to-nitrite reduction, chlorhexidine-containing mouthwash prevents the conversion of dietary nitrate to the active nitrite precursor [3].

This finding has two practical implications. First, athletes supplementing with beetroot juice should avoid using antibacterial mouthwash in the hours preceding and following supplementation. Second, the mouthwash interference provides compelling mechanistic evidence that the oral bacteria-dependent reduction step is essential for nitrate's ergogenic effect, ruling out alternative mechanisms that don't require this conversion.

Nitrate Source: Beetroot Juice vs. Sodium Nitrate vs. Vegetables

Most research has used beetroot juice as the nitrate vehicle due to its high nitrate concentration (3-5 mmol per 100mL of concentrated juice), commercial availability, and the ability to create nitrate-depleted beetroot juice as a visually identical placebo. However, equivalent nitrate from sodium nitrate supplements or high-nitrate vegetables (spinach, arugula, lettuce) provides similar performance benefits, confirming that nitrate is the active component rather than beetroot-specific phytochemicals [4].

Practical considerations favor commercially concentrated beetroot shots (typically 70mL providing 5-8 mmol nitrate) for athletic use due to portion control precision and convenience, though athletes who can reliably consume adequate quantities of high-nitrate vegetables achieve similar benefits through dietary means.

Interaction with Training Status and Oxygen Availability

The gradient of nitrate responsiveness across training levels reflects a fundamental characteristic of the nitrate-nitrite-NO pathway: its benefits are greatest when conventional oxygen-dependent NO synthesis is most limited. In conditions of tissue hypoxia and acidosis — the state of intensely working muscles — nitrite reduction to NO is strongly favored, while less trained individuals who experience more pronounced exercise-induced hypoxia show greater pathway activation [5].

This interaction also explains why the benefits are most pronounced at moderate rather than near-maximal exercise intensities: at near-maximal intensities, oxygen delivery (cardiovascular capacity) rather than mitochondrial efficiency becomes the primary limiting factor, shifting performance determinants away from the specific mechanisms nitrate addresses.

<h2>Practical Recommendations</h2> <h3>Dosing and Timing Protocol</h3> <p><strong>Acute (single event):</strong> - Consume 500mL of beetroot juice (providing ~6-8 mmol nitrate) or a commercially concentrated beetroot shot (70mL, ~5-8 mmol nitrate) 2-3 hours before exercise - The 2-3 hour window allows oral bacteria to convert nitrate to nitrite, with plasma nitrite peaking at the time of exercise onset</p> <p><strong>Loading (2-3 day protocol, preferred for competition):</strong> - Consume 500mL beetroot juice or equivalent nitrate daily for 2-3 days leading up to the event - Continue with a dose 2-3 hours before the event itself - Loading elevates tissue nitrate stores and provides more sustained NO availability during competition</p> <table> <thead> <tr> <th>Protocol</th> <th>When to Use</th> <th>Nitrate Dose</th> </tr> </thead> <tbody> <tr> <td>Single dose</td> <td>Training sessions, casual competition</td> <td>6-8 mmol (500mL juice or 70mL shot)</td> </tr> <tr> <td>3-day loading</td> <td>Important competition</td> <td>Same dose daily for 3 days</td> </tr> <tr> <td>Chronic daily</td> <td>Sustained training performance</td> <td>3-6 mmol/day from dietary sources + supplementation</td> </tr> </tbody> </table> <h3>Nitrate Sources by Concentration</h3> <table> <thead> <tr> <th>Source</th> <th>Nitrate Content</th> <th>Notes</th> </tr> </thead> <tbody> <tr> <td>Beetroot concentrated shots</td> <td>~5-8 mmol per 70mL</td> <td>Most practical for athletes</td> </tr> <tr> <td>Fresh beetroot juice</td> <td>~3-5 mmol per 100mL</td> <td>Lower concentration, more volume needed</td> </tr> <tr> <td>Spinach (raw)</td> <td>~3-5 mmol per 100g</td> <td>Practical dietary source</td> </tr> <tr> <td>Arugula (raw)</td> <td>~4-6 mmol per 100g</td> <td>Very high concentration, useful dietary source</td> </tr> <tr> <td>Lettuce (romaine)</td> <td>~1-2 mmol per 100g</td> <td>Moderate concentration</td> </tr> <tr> <td>Celery</td> <td>~1-3 mmol per 100g</td> <td>Moderate concentration</td> </tr> </tbody> </table> <h3>Critical Practical Considerations</h3> <ol> <li><strong>Avoid antibacterial mouthwash</strong>: Do not use chlorhexidine-based mouthwash within 6-12 hours of nitrate supplementation — it destroys the oral bacteria required for nitrate conversion and will eliminate ergogenic benefit</li> <li><strong>Avoid antacids/PPIs</strong>: Agents that reduce gastric acid may impair nitrite conversion; timing supplementation away from antacid use is advisable</li> <li><strong>Expect pink/red urine and stool</strong>: Beetroot consumption routinely causes beeturia (red/pink urine) and red-tinged stool in many individuals — this is harmless but can be alarming <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> unexpected</li> </ol> <h3>Who Benefits Most</h3> <ul> <li><strong>Recreational to moderately trained endurance athletes</strong>: Greatest expected performance improvement</li> <li><strong>Athletes competing in moderate-intensity sustained efforts (60-90 minutes)</strong>: Sweet spot for economy benefits</li> <li><strong>Resistance training athletes using high-repetition protocols</strong>: Meaningful muscular endurance benefit</li> <li><strong>Athletes competing in hot environments</strong>: Vasodilatory effects enhance thermoregulatory capacity</li> </ul> <h3>Who Benefits Less</h3> <ul> <li><strong>Elite endurance athletes</strong> (VO₂max 65mL/kg/min): Attenuated response; still worth individual testing</li> <li><strong>Pure sprint/power events</strong> (30 seconds): Economy improvements irrelevant for very short durations</li> <li><strong>Athletes with already high dietary nitrate intake</strong>: Less room for supplementation to add beyond habitual levels</li> </ul>