In the autumn of 2007, a group of physiologists at the Karolinska Institute in Stockholm published a result they described, in the paper itself, as "highly surprising". Nine well-trained young men had cycled on an ergometer after three days of taking sodium nitrate, an ordinary salt of the kind found in celery, spinach and beetroot, and their bodies had used less oxygen to do the same work. Not more power for more fuel; the same power for less. Gross efficiency rose from 19.7 to 21.1 per cent, with no rise in lactate and no change in heart rate [1].

This was not supposed to happen. The oxygen cost of a given workload had been treated as a fixed property of human muscle for the best part of a century. Nitrate, meanwhile, was regarded as inert at best and faintly suspect at worst, the thing regulators measured in drinking water. That the two should be connected, and that the connection should lead to a root vegetable, took a few years to sink in. When it did, the vegetable in question began turning up in the fridges of professional cycling teams, and a Baltic garden staple, the red beet that has been boiled for soup and grated into salads here for centuries, found itself at the centre of one of the most carefully studied questions in sports science.

The molecule that won a Nobel Prize

To understand why a beet can change how much oxygen you burn, you have to start with a gas. Nitric oxide, two atoms and a lifespan of a few seconds, is the signal the lining of your blood vessels uses to tell the muscle around them to relax. When it is released, arteries widen, blood flow increases, platelets become less sticky, and the mitochondria inside working muscle adjust how they use oxygen. Robert Furchgott, Louis Ignarro and Ferid Murad received the 1998 Nobel Prize in Physiology or Medicine for working out that this fleeting gas was the body's master vasodilator [2]. We have written about that discovery and the berries that feed into it in The Nobel Prize Hiding in Your Bloodstream; this article is about the plant that does it most directly.

The textbook route to nitric oxide runs from the amino acid L-arginine, through a family of enzymes, and it needs oxygen to work. That is a design flaw, or at least a limitation: the moment you most want more blood flow to a muscle is precisely the moment that muscle is running short of oxygen. Nature, it turns out, installed a second route, and the second route is the one beetroot uses.

The second pathway runs through your tongue

The alternative pathway was mapped in detail in a 2008 review in Nature Reviews Drug Discovery by Jon Lundberg, Eddie Weitzberg and Mark Gladwin, and it is one of the more elegant loops in human physiology [3]. It goes like this. You eat a nitrate-rich plant. The nitrate is absorbed in the upper gut and enters the blood, where it does very little. Then something odd happens: your salivary glands actively pull roughly a quarter of it back out of the bloodstream and concentrate it in saliva, at levels many times higher than in plasma. On the back of your tongue live anaerobic bacteria that use that nitrate for their own respiration, and in doing so reduce it to nitrite. You swallow the nitrite. In the acid of the stomach some of it becomes nitric oxide on the spot, and the rest is absorbed into the blood as nitrite, a stable reservoir that tissues can convert to nitric oxide exactly where oxygen is scarce and acidity is high, which is to say inside a hard-working muscle.

This is not a hypothesis; it has been tested in the most direct way imaginable. In 2008, Andrew Webb and colleagues at Barts and The London gave healthy volunteers 500 ml of beetroot juice and watched blood pressure fall by a peak of 10.4/8 mmHg about three hours later, tracking the rise in plasma nitrite [4]. Then they repeated the experiment while asking the volunteers to spit rather than swallow their saliva. The nitrite never rose, and the blood pressure never fell. The same year, a Swedish group showed that an antibacterial mouthwash, used after a nitrate load, markedly attenuated the increase in plasma nitrite, because it killed the bacteria that do the conversion [5]. Whatever a beet is going to do for you, it does through the microbes on your tongue.

Why beetroot, of all things

Nitrate is how a plant carries nitrogen from the soil into its tissues, and some plants carry a great deal of it. In the standard classification published in the American Journal of Clinical Nutrition, vegetables are sorted into bands by nitrate content, and the highest band, above 250 mg per 100 g, contains rocket, spinach, lettuce, celery and red beetroot [6]. Beetroot has one advantage over the leaves on that list: it juices. A 500 ml glass delivers a nitrate dose that would take a mixing bowl of rocket to match, and it delivers it in a form you can drink two hours before a run.

How much is enough has been worked out with some precision. In a 2013 dose-response study at the University of Exeter, Lee Wylie and colleagues gave volunteers concentrated beetroot juice containing 4.2, 8.4 or 16.8 mmol of nitrate, then measured oxygen uptake and how long they could hold a hard effort. The 8.4 mmol dose reduced the oxygen cost of steady exercise and extended time to exhaustion by 14 per cent; doubling it to 16.8 mmol added nothing further, extending it by 12 per cent [7]. The two landmark performance trials, described below, used 500 ml of ordinary beetroot juice containing roughly 5.5 to 6.2 mmol of nitrate [8][9]. That is the working range: somewhere between a large glass and half a litre.

The Exeter experiments

The study that moved beetroot from a curiosity into the training diet was published in the Journal of Applied Physiology in 2009 by Stephen Bailey and Andrew Jones's group at Exeter [8]. Eight men drank 500 ml of beetroot juice a day for six days, or 500 ml of blackcurrant cordial as a placebo, in a double-blind crossover. On beetroot, plasma nitrite roughly doubled, systolic blood pressure came down from 132 to 124 mmHg, and the rise in oxygen uptake at the start of moderate exercise was 19 per cent smaller. Then they rode to exhaustion at a severe intensity. On placebo they lasted 583 seconds on average; on beetroot, 675. An extra minute and a half of hard riding, from a vegetable.

Two years later the same group asked the question that matters to anyone with a race number: does it make you faster? Nine club-level cyclists drank 500 ml of beetroot juice, or the same juice with the nitrate removed, two and a half hours before a 4 km and a 16.1 km time trial [9]. Oxygen uptake during the trials was identical between conditions, but power output was not: 292 watts against 279 over 4 km, 247 against 233 over 16.1 km. The 4 km trial was 2.8 per cent faster, the 16.1 km trial 2.7 per cent faster. The same lungs, the same heart, more work.

The literature has grown enormously since. A 2020 meta-analysis in Medicine & Science in Sports & Exercise pooled 80 studies and found that nitrate supplementation improved exercise performance compared with placebo, with the clearest benefit in recreational and moderately trained people and a smaller effect in elite endurance athletes whose aerobic fitness was already exceptional [10]. That is worth reading the right way round. If you are not a professional, you are the population in which this works best. The International Olympic Committee's 2018 consensus statement on supplements lists dietary nitrate among the small handful, alongside caffeine, creatine, beta-alanine and bicarbonate, for which the evidence of a performance benefit is considered good [11].

Blood pressure: the effect that outlasts the race

Most people who buy beetroot juice are not racing anyone. For them the more important trial was published in Hypertension in 2015 by Vikas Kapil and Amrita Ahluwalia's group in London [12]. Sixty-eight patients with high blood pressure, half of them untreated and half already on medication, drank 250 ml of beetroot juice every day for four weeks, or 250 ml of the same juice with its nitrate stripped out. Blood pressure was measured three ways, and it fell by all three: 7.7/2.4 mmHg in the clinic, 7.7/5.2 mmHg on 24-hour ambulatory monitoring, and 8.1/3.8 mmHg at home. The effect did not fade over the four weeks. Endothelial function improved by about 20 per cent and arterial stiffness fell measurably, and the placebo group saw none of it. The dose was one small glass a day.

The vessels in the brain respond too. A 2011 study at Wake Forest gave older adults, average age 75, a day of high-nitrate eating that included beetroot juice, then imaged their brains, and found increased blood flow to the frontal lobe white matter, the territory that handles planning and attention [13]. It was a small, short study, and it belongs in this article for what it shows about mechanism: the same pathway that helps a cyclist over the last kilometre is opening vessels wherever oxygen is being asked for.

The colour is not decoration

Nitrate is invisible. What you see when you cut a beet is betanin, the chief of a family of pigments called betalains that almost no other food plant makes. Beetroot carries around 300 to 600 mg of betanin per kilogram, and unlike many plant pigments, betalains are absorbed into the bloodstream intact, where they behave as antioxidants and dampen inflammatory signalling [14]. We told the wider story of that pigment in The Color Code. For present purposes the point is that a glass of beetroot juice is two separate arguments in one: a nitrate argument about blood flow and oxygen, and a betalain argument about the chemistry of a plant that spent its life defending itself from light and oxidation in a cold northern field.

One consequence of the pigment deserves a sentence, because it alarms people who have not been warned. In roughly one person in ten, betanin passes through unchanged and turns the urine pink or red for a day. The phenomenon has a name, beeturia, and it is entirely harmless [15].

What to do this week

The research gives unusually clear instructions, so here they are.

If you train. Drink 250 to 500 ml of beetroot juice two to three hours before the session, which is where plasma nitrite peaks [4][9]. For an event, take the same amount daily for the three to six days beforehand, as the Exeter protocol did [8]. Pure pressed beetroot is the most direct route; ours is Red Rabbit, 100% organic beetroot and nothing else, which is deliberately plain because it is meant to be measured out rather than sipped for pleasure.

If you don't. The blood pressure trial used 250 ml a day for four weeks [12]. That is a small glass, and it is easier to keep up when the juice tastes like something you want. Root Rush softens beet with apple and carrot; Ruby Root pairs 30% beetroot with 70% aronia, which brings the anthocyanin side of the blood-flow story into the same glass. If you want the roots, the berry and a ginger shot in one box, the Active Day set was built for exactly this month.

Protect the pathway. Do not use antibacterial mouthwash within a few hours of your beetroot; it kills the bacteria that do the work [5]. Swallow your saliva. Chew your beetroot salad slowly. The loop through the tongue is the whole mechanism, and it is easy to break by accident.

Eat the leaves too. Beet greens are the same species as chard, and leafy vegetables are the other great nitrate source in the diet [6], so a bunch of young beets with the tops on is two vegetables for the price of one.

One line of caution: beetroot is rich in oxalate, so go gently if you have had oxalate kidney stones, and if you take blood-pressure medication the effect adds to it, which is worth a word with your doctor.

Beetroot juice, in short

Beetroot is one of the richest sources of nitrate. Bacteria on the tongue convert that nitrate to nitrite, which the body turns into nitric oxide where oxygen is scarce. Trials show lower oxygen cost, longer endurance, faster time trials and lower blood pressure from 250 to 500 ml a day.

Back to Stockholm

The summary of the Karolinska paper that started all this ends with a line that reads, in hindsight, like an understatement: the mechanism, the authors wrote, "needs to be clarified". It has been. The plant stores nitrogen in its root; the root goes into the press; the juice goes into you; your tongue hands it to a colony of bacteria that turn it into the precursor of the body's own vasodilator; and somewhere in a working muscle, at the moment oxygen runs short, a gas that lives for a few seconds opens a vessel that would otherwise have stayed closed.

None of this was designed for cyclists. It is simply what happens when a vegetable that has grown in northern soil since before there were written recipes for it meets a body that evolved eating it. The athletes just noticed first.

Frequently asked questions

How long before exercise should I drink beetroot juice?

Two to three hours. Plasma nitrite, the form your body uses, peaks around two and a half to three hours after a dose [4][9]. For an important event, a daily glass for three to six days beforehand builds a higher baseline [8].

How much beetroot juice do I need for an effect?

The performance trials used 500 ml of ordinary beetroot juice, about 5.5 to 6.2 mmol of nitrate [8][9]. The dose-response work found the benefit levels off above roughly 8 mmol [7]. The blood pressure trial used 250 ml a day [12]. Between a large glass and half a litre is the evidence-based range.

Does mouthwash really cancel out beetroot juice?

Antibacterial mouthwash does. The conversion of nitrate to nitrite happens on the tongue, and a 2008 study showed that a chlorhexidine-type rinse markedly attenuated the rise in plasma nitrite after a nitrate load [5]. Brush normally; just skip the antiseptic rinse around the time you drink it.

Why is my urine pink after beetroot?

That is beeturia: the red pigment betanin passing through unchanged. It happens to roughly one person in ten, it varies from person to person and from meal to meal, and it is harmless [15].

References

1. 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.
2. The Nobel Assembly at Karolinska Institutet. The Nobel Prize in Physiology or Medicine 1998: press release. Stockholm, 12 October 1998. nobelprize.org.
3. 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.
4. 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.
5. Govoni M, Jansson EÅ, 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.
6. 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.
7. Wylie LJ, Kelly J, Bailey SJ, et al. Beetroot juice and exercise: pharmacodynamic and dose-response relationships. J Appl Physiol. 2013;115(3):325–336.
8. 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.
9. Lansley KE, Winyard PG, Bailey SJ, et al. Acute dietary nitrate supplementation improves cycling time trial performance. Med Sci Sports Exerc. 2011;43(6):1125–1131.
10. Senefeld JW, Wiggins CC, Regimbal RJ, Dominelli PB, Baker SE, Joyner MJ. Ergogenic effect of nitrate supplementation: a systematic review and meta-analysis. Med Sci Sports Exerc. 2020;52(10):2250–2261.
11. 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.
12. Kapil V, Khambata RS, Robertson A, Caulfield MJ, Ahluwalia A. Dietary nitrate provides sustained blood pressure lowering in hypertensive patients: a randomized, phase 2, double-blind, placebo-controlled study. Hypertension. 2015;65(2):320–327.
13. Presley TD, Morgan AR, Bechtold E, et al. Acute effect of a high nitrate diet on brain perfusion in older adults. Nitric Oxide. 2011;24(1):34–42.
14. Clifford T, Howatson G, West DJ, Stevenson EJ. The potential benefits of red beetroot supplementation in health and disease. Nutrients. 2015;7(4):2801–2822.
15. Mitchell SC. Food idiosyncrasies: beetroot and asparagus. Drug Metab Dispos. 2001;29(4 Pt 2):539–543.