Nitrate supplementation has become one of the most researched topics in modern sports science. While in the past nitrates were considered a mere by-product of metabolism, today we know that they play a key role in regulating blood flow, muscle contraction and cellular energetics. The main natural source of these substances in sports nutrition is beetroot juice. Let us take a detailed look at the specific scientific studies that have examined the effect of nitrates on the human body, and at the real results athletes have achieved.
The physiological mechanism: how does the body produce nitric oxide?
Nitrates (NO3−) taken in from food are, after absorption in the small intestine, concentrated in our salivary glands – roughly 25 % of the amount ingested is secreted into saliva. Bacteria in the mouth then reduce these nitrates to nitrites (NO2−). After the saliva is swallowed, the final conversion into nitric oxide (NO) takes place in the acidic environment of the stomach and subsequently in the bloodstream.
This process of conversion into NO is most effective in conditions of low oxygen availability (hypoxia) and low pH. Those are exactly the conditions that naturally arise in intensely working skeletal muscle. The whole chain – including the second, oxygen-dependent pathway via L-citrulline – is summarised in the following diagram:
A simplified diagram of nitrate metabolism and nitric oxide production (adapted from Jeukendrup & Gleeson, 2025).
Scientific experiments have confirmed that if an athlete uses an antibacterial mouthwash which kills off the oral bacteria, the rise in nitrite levels in blood plasma after taking nitrates is drastically blunted.
The results of scientific studies
What makes nitrates absolutely unique is their ability to reduce the oxygen “price tag" of submaximal exercise. This was previously considered more or less unchangeable in human physiology. Here is an overview of the key studies and their results:
| Study | Sample & protocol | Key result |
|---|---|---|
| Larsen et al. 2007 |
9 athletes · 3 days sodium nitrate 0.1 mmol/kg |
−5 % VO₂ · higher muscle efficiency (19.7 → 21.1 %) |
| Bailey et al. 2009 |
8 men · 6 days 5.6 mmol (0.5 l of beetroot) |
+16 % time to exhaustion · −23 % slow component of VO₂ |
| Lansley et al. — running 2011 |
6 days · 6.2 mmol run to exhaustion |
+15 % time to exhaustion |
| Lansley et al. — time trial 2011 |
9 cyclists · acute dose 6.2 mmol, 2.5 h in advance |
4 km: +2.8 % · 16.1 km: +2.7 % |
| Cermak et al. 2012 |
12 cyclists · 6 days 8 mmol |
10 km faster (−0.2 min) · +6 W power |
The same pattern repeats across the studies: lower oxygen consumption for the same work, a longer time to exhaustion and faster time trials.
What happens inside the muscle: three cellular adaptations
Researchers did not stop at measuring times on the track, but examined muscle cells directly under the microscope and using magnetic resonance. They uncovered three revolutionary cellular adaptations:
| Cellular adaptation | Source | Key finding |
|---|---|---|
| Mitochondrial saving lower ANT expression → less proton leak |
Larsen et al. 2011 |
+19 % P/O ratio (more ATP per unit of oxygen) |
| Better handling of calcium ↑ calsequestrin 1 and the DHP receptor |
Hernández et al. 2012 |
↑ Ca²⁺ in type II fibres → faster force |
| Increased blood flow preferentially to fast type II fibres |
Ferguson et al. 2013 |
+38 % blood flow to the muscles |
Team and intermittent sports
The study by Wylie et al. (2013) confirmed that nitrate supplementation demonstrably improves performance in tests that simulate movement in team sports too (repeated sprints at high intensity with short rests). That opens the door to nitrates outside the purely endurance community as well (football, ice hockey, basketball).
How long does the effect last – does supplementation need to be cycled?
Athletes often ask whether the body gets used to beetroot (develops a tolerance) if they drink it for a longer time. The study by Vanhatalo et al. (2010) followed athletes over 15 days of continuous beetroot use. It turned out that the reduction in oxygen consumption during submaximal exercise occurs as early as 2.5 hours after the first dose and remains completely unchanged in strength after 5 and after 15 days. The body therefore does not develop a tolerance and nitrates work even with long-term supplementation.
The relationship of nitrates to VO2max and the redefinition of endurance performance
The traditional model of endurance performance (Coyle, 1995) rests on three pillars: maximum oxygen uptake (VO2max) as the absolute ceiling of the aerobic system, fractional utilisation of VO2max (the sustainable percentage of this ceiling without accumulating lactate) and economy of movement (the amount of oxygen used per unit of work). While classic training methods aim primarily at raising the absolute ceiling, nitrate supplementation brings a shift by selectively optimising precisely the economy of movement – it produces a so-called lower oxygen cost.
Nitrates demonstrably reduce oxygen consumption during submaximal constant-load exercise by roughly 5 %, and that without any compensatory involvement of anaerobic metabolism (both pH and lactate remain stable). This unique phenomenon is mediated by two cellular mechanisms:
Increased mitochondrial efficiency: Larsen et al. (2011) showed that nitrates reduce the expression of the mitochondrial protein ANT (adenine nucleotide translocase) on the inner mitochondrial membrane, which limits proton leak. The result is a 19% increase in the P/O ratio (the amount of ATP synthesised per unit of oxygen consumed), which correlates closely (r = −0.80) with the reduction in total oxygen consumption during exercise.
Reduced energy demands of contraction: Nitrates demonstrably spare muscle phosphocreatine (PCr) stores and dampen the build-up of fatigue metabolites such as ADP and inorganic phosphate (Pi). This reduces the amount of ATP needed to produce muscle force – among other things through lower energy demands of the calcium pump.
A practical supplementation protocol
Effective dose: The ideal ergogenic dose is between 6 and 8 mmol (about 370 to 500 mg) of nitrates. Doses higher than 16 mmol bring no further improvement.
Timing: While the level of nitrates in the blood rises quickly, the key nitrites peak only 2 to 3 hours after ingestion. The juice or concentrate therefore has to be drunk that far in advance.
Acute vs. chronic dosing: In ordinary recreational athletes even a single acute dose before a race works. However, in highly trained and elite endurance athletes (VO2max > 60 ml/kg/min) a single dose often fails. For protein adaptations in the mitochondria to occur in them, a chronic protocol lasting 3 to 15 days is essential.
A standardised concentrate that solves the three biggest weaknesses of classic beetroot juice:
Specific features of nitrate supplementation in elite athletes
Applying dietary nitrates in highly trained and elite endurance athletes (typically VO2max > 60–70 ml/kg/min) presents a specific challenge because of the so-called ceiling effect – these individuals have already maximised their physiological systems. Clinical studies in them often recorded neither a reduction in oxygen consumption nor an improvement in performance after an acute dose; this was confirmed for example by Peacock et al. (2012) in elite cross-country skiers (VO2max ≈ 70 ml/kg/min) or by Bescós et al. (2012) in trained triathletes and cyclists. This blunted ergogenic effect has several training-related causes:
Increased endogenous NO production: Elite athletes show naturally high nitric oxide synthase (NOS) activity and higher baseline levels of nitrites in plasma.
High muscle capillarisation: A dense capillary network ensures excellent muscle perfusion and oxygenation during submaximal exercise. Since the reduction of nitrites (NO2−) to active NO takes place predominantly in conditions of local hypoxia and low pH, the high oxygen availability in trained muscle naturally suppresses this pathway.
Distribution of muscle fibres: Nitrates selectively affect the contractility and blood supply of fast type II fibres – elite endurance athletes, however, have muscle made up predominantly (often more than 80–90 %) of slow type I fibres.
A breakthrough in time trials and the importance of individuality. Despite these limits, the systematic review and meta-analysis by Silva et al. (2023), focused exclusively on elite athletes, showed that acute nitrate supplementation leads to a statistically significant reduction in time in time trials (against-the-clock tests) – most consistently in cyclists and when given in the form of beetroot juice (BRJ). The key to understanding this is the extreme individual variability: Wilkerson et al. (2012) in a 50-mile time trial found no overall group effect, but did discover a very close correlation (r = −0.83) between the individual rise in plasma nitrites after beetroot and the speeding up of the resulting time (the concept of responders vs. non-responders).
To overcome this biological resistance, elite athletes need to reach for chronic loading protocols (3–15 days), higher doses (8 mmol / 500 mg of nitrates) and to target the intense anaerobic phases of an effort – the decisive breaks, surges and finishes.
Safety and health
Scientific authorities warn against using pure nitrate or nitrite salts because of the risk of toxicity and of developing methaemoglobinaemia (Lundberg et al. 2011). By contrast, according to experts, consuming natural beetroot juice is very unlikely to be dangerous (Jones et al. 2011; Lundberg et al. 2011). Vegetables naturally contain a high amount of antioxidants (e.g. vitamin C) and polyphenols, which reliably block the formation of potentially carcinogenic nitrosamines in the stomach (Mirvish et al. 1998).
Discolouration of urine (beeturia). In some people (roughly 10–14 % of the population) beetroot can harmlessly colour urine or stools pink or red. This is so-called beeturia, caused by the natural pigments of beetroot (betalains) – it is not a sign of any health problem and once the pigments are excreted, the colour disappears on its own.
Combining nitrates and L-citrulline: maximum synergy of two pathways
If you are looking for the absolute maximum in performance, the latest studies point to an exceptional benefit of taking nitrates and L-citrulline together. The human body produces nitric oxide (NO) via two independent pathways which complement each other perfectly:
The production of NO from amino acids. L-citrulline is safely converted into arginine in the body and feeds this pathway. It works excellently in aerobic conditions with plenty of oxygen.
It is provided by dietary nitrates from beetroot. This pathway is fully activated precisely when the first pathway fails because of a lack of oxygen and acidification (hypoxia, acidosis).
A study in trained triathletes (Burgos et al., 2022)
In this 9-week randomised, double-blind study in trained triathletes (VO2max ~59 ml/kg/min) the researchers tested the combination of 3 g/day of L-citrulline (CIT) + 2.1 g/day of beetroot extract (BR), 300 mg of nitrates.
Protection of the hormonal profile: While in the groups taking the supplements on their own or the placebo there was a drop in testosterone over the course of a demanding season, the CIT + BR combination reliably prevented this drop.
Reduced stress and better recovery: The combination group showed a significantly lower level of the stress hormone cortisol and an improvement in the testosterone/cortisol ratio (T/C ratio), which indicates an excellent anabolic state and protection of muscle mass from breakdown.
A real increase in performance: The triathletes in the combination group (CIT+BR) achieved the statistically greatest increase in the distance covered in the Cooper test after 9 weeks of supplementation.
Exactly the combination described above – it covers both nitric oxide production pathways in one package:
Conclusion for athletes
Nitrates from beetroot are among the handful of supplements whose ergogenic effect rests on genuinely firm scientific foundations – they are even among the five food supplements with the strongest evidence for performance according to the consensus of the International Olympic Committee. Across dozens of studies the same pattern repeats: a lower oxygen “price" of movement, higher mechanical efficiency of the muscle, a longer time to exhaustion and measurably faster times in time trials. This is not an effect at the level of statistical error – we are talking about improvements of a few per cent, which in the finishing straight is the difference between a personal best and an average race.
For practice it is enough to remember three things. The dose: 6 to 8 mmol of nitrates (roughly 400–500 mg) is the optimum; higher doses add nothing more. The timing: nitrites in the blood peak only 2–3 hours after ingestion, so drink the beetroot that far in advance, not on the start line. And the oral bacteria: on race day skip the antibacterial mouthwash, otherwise you will block the whole effect yourself.
A recreational athlete will benefit even from a single acute dose before a race. An elite endurance athlete with a VO2max above 60 ml/kg/min should reach for a chronic protocol (3–15 days), so that the slower cellular adaptations in the mitochondria have time to get going too. And if you want to go to the absolute maximum, combining it with L-citrulline covers both nitric oxide production pathways at once – the aerobic one and the one that kicks in when the body is running out of oxygen.
Beetroot is not a miracle that turns an average runner into an elite one. It is, however, one of the few legal, safe and scientifically supported ways of getting a few per cent more out of your own body – and in endurance or performance sport it is precisely those percentages that decide.
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