Over the past fifteen years, beetroot juice has gone from a garden vegetable to one of the best-studied sports supplements. The reason is nitrates, which the body converts into nitric oxide. The editorial team explains what dietary nitrates are, how they work, and why even the bacteria on your tongue matter for their action.
What dietary nitrates are
Nitrate (NO₃⁻) is a simple inorganic anion that plants absorb from the soil as a source of nitrogen. It is accumulated most by leafy and root vegetables: arugula, spinach, lettuce, celery, chard and, of course, red beetroot. Beetroot became the 'face' of this category of supplements because it is easy to make a concentrated juice from it with a predictable nitrate content.
For a long time nitrates were viewed solely as an undesirable contaminant of food and drinking water. Regulatory bodies set limits for them, and in the public sphere they were associated with 'chemicals' in the fields. The situation changed in the 2000s, when Swedish researchers Lundberg and Weitzberg showed that dietary nitrate is an important reserve source of nitric oxide (NO) in the body (Lundberg et al., 2008).
It is important to distinguish inorganic nitrates from food and organic nitrates - medications such as nitroglycerin or isosorbide dinitrate. These are different classes of compounds with different pharmacology. When we speak of 'beetroot nitrates,' we mean precisely the inorganic nitrate found in vegetables.
| Nitrate content category | Examples of vegetables |
|---|---|
| Very high | Arugula, spinach, lettuce, celery (stalks), chervil, watercress, red beetroot |
| High | Celeriac, Chinese cabbage, endive, fennel, kohlrabi, leek, parsley |
| Medium and low | Cabbage, carrots, cucumbers, pumpkin, tomatoes, onions, potatoes |
The classification is given according to the review by Hord and colleagues (2009). The actual content in a particular vegetable can vary several-fold depending on the variety, soil, fertilizers, lighting, and time of harvest, which is why standardized juices are used for research.
The nitrate - nitrite - nitric oxide pathway
Nitric oxide is a signaling molecule that relaxes the smooth muscle of blood vessels, regulates blood flow, affects muscle contraction and mitochondrial function. The classic pathway of its synthesis is from the amino acid L-arginine with the participation of NO synthase enzymes, which require oxygen. The nitrate pathway is an alternative one and works most efficiently precisely when oxygen is scarce.
After consuming beetroot, nitrate is quickly absorbed into the blood. A significant part of it is taken up by the salivary glands and concentrated in saliva. On the surface of the tongue live bacteria that reduce nitrate to nitrite (NO₂⁻). Swallowed nitrite is partly converted into NO already in the acidic environment of the stomach, and partly absorbed and circulated in the blood.
In tissues where oxygen tension is reduced and the environment is acidic - for example, in muscles during intense exercise - nitrite is reduced to NO with the participation of deoxyhemoglobin, myoglobin, and other proteins. In this way the system 'turns on' precisely where and when nitric oxide is most needed.
Oral bacteria are a critical link in the chain. The study by Govoni and colleagues (2008) showed that rinsing the mouth with an antibacterial mouthwash sharply reduces the rise of nitrite in plasma after nitrate intake. In other words, without the 'right' oral microflora, beetroot juice loses a significant part of its action.
How nitrates affect muscles and blood vessels
The most interesting discovery for sports science was made by Larsen and colleagues (2007): after several days of taking sodium nitrate, the oxygen 'cost' of submaximal work on a cycle ergometer decreased. A person performed the same work while expending less oxygen. For physiology this was unexpected, because the efficiency of muscular work was considered a practically unchangeable quantity.
The group of Andrew Jones from the University of Exeter reproduced this effect with beetroot juice (Bailey et al., 2009) and showed an extension of time to exhaustion during high-intensity work. The proposed mechanisms include a reduction in the energy cost of the ion pumps' work in muscle fibers and an improvement in mitochondrial efficiency.
- Blood vessels:dilation, improved blood flow, a moderate reduction in blood pressure (Webb et al., 2008).
- Muscles:reduced oxygen cost of work, possible enhancement of the contractile function of fast type II fibers.
- Metabolism:less phosphocreatine expenditure per unit of work in some studies.
Interestingly, the effects on fast muscle fibers may explain why nitrates sometimes help in interval and team sports, not just in endurance. However, this area is less studied, and the results there are inconsistent (Jones et al., 2018).
Who benefits most from nitrates
The effect of nitrates is not the same in different people. The most consistent results have been obtained in amateurs and moderately trained people. In highly qualified endurance athletes the effect is often smaller or absent (Porcelli et al., 2015). One explanation is that they already have high NO synthase activity, a developed capillary network, and a different proportion of muscle fibers.
The duration and type of exercise also play an important role. Nitrates performed best in work lasting from a few to about 30-40 minutes, as well as in repeated high-intensity sprints. For very long distances and for maximal strength the evidence is weaker.
Possible benefit under hypoxic conditions - for example, at altitude - is theoretically logical, since the nitrite pathway is most active precisely when oxygen is lacking. However, data from studies at altitude are contradictory, so beetroot nitrates cannot be called a 'magic remedy for the mountains.'
In its consensus on dietary supplements (Maughan et al., 2018), the International Olympic Committee placed nitrates in the small group of supplements with a sufficient evidence base for improving performance - alongside caffeine, creatine, beta-alanine, and sodium bicarbonate. Nitrates are not on the WADA Prohibited List.
Safety: what to know in advance
For most healthy people, consuming beetroot juice in the doses used in studies is safe. The most common 'side effect' is pink or red coloring of the urine and stool (beeturia), which is not dangerous but can be alarming if you are not aware of it.
At the same time, nitrates lower blood pressure, so people with hypotension and those taking antihypertensive drugs or PDE-5 inhibitors need to consult a doctor. Beetroot also contains oxalates, which is important for people prone to kidney stones.
Separately, we emphasize: concentrated nitrate salts, and especially sodium nitrite, are not dietary supplements for home use. Nitrite in high doses causes methemoglobinemia, and fatal poisonings from this substance are known. The source of nitrate for an athlete should be vegetables or standardized juices.
We cover side effects and contraindications in more detail in separate articles.
Editorial conclusions
Beetroot nitrates are inorganic nitrates from vegetables which, through the 'nitrate - nitrite - nitric oxide' chain, can dilate blood vessels and make muscular work more economical. A critical role in this process is played by the bacteria of the oral cavity.
The effect is most noticeable in amateurs and in exercise of moderate duration, whereas in elite-level athletes it is less predictable. Nitrates have one of the best evidence bases among sports supplements and are permitted by WADA.
Our materials 'The benefits of beetroot nitrates for athletes: the evidence base,' 'How to take beetroot nitrates,' and 'Side effects of beetroot nitrates' will help continue the topic.
References
- Lundberg JO, Weitzberg E, Gladwin MT. The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics. Nat Rev Drug Discov. 2008;7(2):156–167.
- Hord NG, Tang Y, Bryan NS. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. Am J Clin Nutr. 2009;90(1):1–10.
- Larsen FJ, Weitzberg E, Lundberg JO, Ekblom B. Effects of dietary nitrate on oxygen cost during exercise. Acta Physiol (Oxf). 2007;191(1):59–66.
- Bailey SJ, Winyard P, Vanhatalo A, et al. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol. 2009;107(4):1144–1155.
- Govoni M, Jansson EA, Weitzberg E, Lundberg JO. The increase in plasma nitrite after a dietary nitrate load is markedly attenuated by an antibacterial mouthwash. Nitric Oxide. 2008;19(4):333–337.
- Webb AJ, Patel N, Loukogeorgakis S, et al. Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertension. 2008;51(3):784–790.
- Porcelli S, Ramaglia M, Bellistri G, et al. Aerobic fitness affects the exercise performance responses to nitrate supplementation. Med Sci Sports Exerc. 2015;47(8):1643–1651.
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
