Beetroot Juice

Does it work?

Introduction

It is said there are three laws of sports supplements:

  • If it works, it’s probably illegal (in sport)
  • If it is legal, it probably doesn’t work
  • There may be exceptions

Professor Ron Maughan1

Well, research emerging since 20072 suggests we may have a new candidate for the latter category. That candidate? Dietary nitrates (NO3-).

Some Biochemistry

Nitric oxide (NO), discovered in the late ‘80s3, is an important regulator of several physiological processes. Classically, nitric oxide production was thought to only occur via a family of enzymes known as ’Nitric Oxide Synthases’ (NOS)6. The complex reactions of these enzymes involve L-arginine (an amino acid) and are dependent on a number of chemical components, including oxygen9. Crucially, this pathway is compromised under the physiological conditions generally seen during exercise5,11. It was only relatively recently (mid-90s) that an alternative pathway was identified7,8, and this pathway is actually potentiated under exercise conditions9. Fundamentally, this pathway involves the conversion of nitrAte (NO3-), into nitrIte (NO2-), and subsequently nitric oxide (NO). The mechanism by which this occurs is intriguing:

  • Nitrates are ingested as part of the diet (mostly from vegetables).
  • Those nitrates reach the stomach where they are absorbed into the circulation.
  • ~60% of those circulating nitrates are excreted in urine, while ~25% are concentrated in the saliva.
  • Bacteria on the surface of the tongue convert salivary nitrates into nitrites, which are then swallowed.
  • Some of the nitrites pass through the stomach and are absorbed into the circulation from the intestine
  • Circulating nitrites can then be converted into nitric oxide at body tissues where there is a lack of oxygen or an increase in acidity (i.e. exercise).

^Adapted from references 9 & 10.

sources and uses of nitric oxide in the human Bailey et al.9

Nitrates and Performance

In short, supplementation with dietary nitrates has been shown to improve submaximal exercise efficiency, and enhance exercise tolerance at higher-intensities—both of which have the potential to improve performance. It is a fundamental tenet of exercise physiology that oxygen consumption for a given workload, for any given individual, is fairly consistent11, regardless of training status12. Therefore, that nitrate consumption can affect this seemingly immutable characteristic is quite remarkable. The mechanisms underlying these performance-enhancing effects remain unclear4, however, those mechanisms underlying improved efficiency and those underlying high-intensity performance may well be independent4. Some of the postulated mechanisms include:

  • Improved efficiency of muscular contraction9,11 (less energy used for given level of force production.)
  • Improved mitochondrial efficiency12 (mitochondria are often described as the ‘powerhouses’ of cells13, and are the centres of aerobic energy production.)
  • Enhanced blood flow to fast-twitch muscle fibres4.
  • More effective distribution of blood to working muscles11.

Sources of Nitrates

Some readers will be familiar with ‘nitrates’ as a harmful substance (e.g. a carcinogen). However, recent evidence is challenging this view18, and when nitrates are consumed from vegetables (rather than nitrate salts, e.g. sodium nitrate) negative effects are actually reversed15. Early studies2 of dietary nitrates used pharmacological sodium nitrate (NaNO3) as the source, which is perhaps not ideal as:

  • This can cause blood nitrite levels to rise more abruptly (compared to vegetable sources), and potentially reach toxic levels4.
  • Individuals can develop a tolerance16.
  • There are various negative health effects associated with NaNO315.

Consequently, in 2009 researchers begun looking at supplementing dietary nitrates by way of beetroot juice11. The vegetables with the highest nitrate concentration, according to examine.com are: beetroot, celery, cress, chervil, lettuce, spinach, swiss chard, radishes, and rocket17. Green leafy vegetables generally have the highest nitrate content, however, beetroot is often the preferred source due to its palatability17.

Research Overview

Research into the ergogenic effects of dietary nitrates is still in its infancy, but early results are promising14. For example:

NB: TTE = ‘Time to Exhaustion’, subjects exercise at a constant high-intensity work rate and are timed to see how long they can sustain it for.

  • 500 mL of beetroot juice, taken for 6 days, improved cycling efficiency (5%) and TTE (16%) in recreationally active males11.
  • 500mL of beetroot juice per day, for 15 days, immediately (i.e. 2.5 hrs after the first supplementation) improved submaximal cycling efficiency by 5% and this was maintained for the duration of the study period—i.e. subjects did not become tolerant/insensitive.23.
  • 500 mL of beetroot juice, taken for 4–6 days, improved walking efficiency (12%) and submaximal running efficiency (7%) in recreationally active males. TTE was increased by (15%)19.
  • Competitive male cyclists consumed 500 mL of beetroot juice 2.5 hrs before a 4 km & 10 mile laboratory TT. The 4 km TT improved by 2.8%, and the 10 mile improved by 2.7%, following beetroot juice. Cyclists were able to produce a greater power output for the same level of oxygen consumption20.
  • Consumption of a single Beet It shot, consumed 2.5 hrs before testing, allowed trained free-divers to hold their breath 11% longer22.
  • Trained male cyclists consumed a single Beet It shot 3 hrs before completing performance tests at a simulated altitude of 2500 m (i.e. TDF mountain stages). Beetroot juice improved submaximal cycling efficiency (6.8%) and 10 mile TT performance (2.9%)10.
  • Competitive male cyclists consumed 500 mL of beetroot juice 2.5 hrs before a 50 mile laboratory TT (sounds like fun!). 3/8 of the participants were classed as non-responders**, but those who did respond saw a performance improvement of 2%21.

**A ‘responder’ has been defined as an individual who shows an increase in blood nitrite concentration greater than 30% following nitrate supplementation21. ‘Non-responders’ may require a larger dose of nitrates to elicit performance enhancement, but the explanation for the existence of responders and non-responders is currently unknown4.

Studies using active, but not trained, participants have generally reported an improvement in TTE of 16-25%6, which would be expected to improve performance (i.e. TT time) by 1-2%24. A recent literature review found that performance improvements within trained athletes were in the order of 0.9%, though findings within this population group are far less consistent14. It is also interesting to note that beetroot juice has been shown to have particularly positive effects during the final stages of time-trial performances15,21—evidence that it might improve your finishing ‘kick’?

Beetroot Juice and Elite Athletes

As mentioned above, the ergogenic effects of beetroot juice seem to be far less consistent in trained athletes14. Why?

  • Highly-trained endurance athletes generally have a higher baseline nitrate/nitrite pool10,12, reducing the effects of dietary supplementation.
  • The capacity of the NOS pathway is thought to be higher in trained endurance athletes12, and the conditions known to inhibit it are likely attenuated as a result of training6.
  • Highly-trained endurance athletes are expected to have a greater density (+ more efficient) mitochondria and better muscle oxygenation4,6,14. As such, there is less potential for improvement through the suggested mechanisms of nitrates.
  • Competitive athletes generally have less scope for performance improvements, making it difficult to discern a positive effect as a result of nitrate supplementation6. For example, a performance improvement of less than 1%, while meaningful athletes25, is difficult to distinguish from measurement error and day-to-day variability.

Implications and Recommendations

  • Those looking to increase their intake of nitrates should do so via vegetable sources (rather than pharmacological supplements), as this reduces the risk of illicit substance contamination, and will also confer complementary health benefits14,18 (e.g. reduced blood pressure).
    • Note that the nitrate content of vegetables can vary substantially as a result of growing conditions17,27. As such, the use of Beet It juice/shots is advised as it can provide a fairly reliable dose.
    • 62 mg = 1 mmol (inorganic nitrate)17
  • Performance enhancement following beetroot juice consumption seems to be dependent on the increase in blood nitrite21. In most people, blood nitrites peak 2–3 hrs post-ingestion4, after which they gradually return to baseline over 24 hrs4.
  • While blood nitrites increase in a dose-dependent manner (i.e. the more you take, the more the levels rise in your blood), an acute nitrate dose of ~8 mmol (equivalent to 2x Beet It shots)** seems to be the ceiling for performance improvement**4.
    • The above figure was obtained from a sample of recreationally active subjects. Elite athletes may require larger dose of nitrates (e.g. 3–4 Beet It shots!4). But note that blood nitrites will take longer (nearer 4 hrs) to peak following a larger dose4.
    • Consuming food (e.g. breakfast) with a beetroot supplement shouldn’t interfere with the effects30.
  • Recall that dietary nitrates are concentrated in the saliva, and subsequently converted into nitrites by bacteria in the mouth. As a result, the rise in blood nitrites can be blunted by spitting28, and by the use of anti-bacterial mouthwash or chewing gum29.
  • The majority of studies on nitrates have examined performance in events lasting less than 30 min6,20. Performance in longer-duration, lesser intensity events is less likely to be as positively affected21,30. Greater metabolic perturbation leads to an increased reliance on the nitrate pathway. The lesser intensity of longer duration events leads to less metabolic disturbance, and as a result the effect of nitrate supplementation seems to be reduced21.
  • A ‘loading’ protocol with nitrates is probably more effective than a single dose14. However, sustained beetroot supplementation could potentially blunt training adaptations, due its antioxidant properties26. Therefore, nitrate use is probably best reserved for races and key training sessions. An acute dose (2–3 hrs prior) of 2x Beet It shots/750 mL of juice is likely sufficient to enhance high-quality training sessions. However, a loading period (>6 days), of similar daily doses, is advisable prior to races.

References

  1. Burke, L., Desbrow, B. and Spriet, L. Caffeine for Sports Performance. Human Kinetics. 2013.
  2. Larsen, F., Weitzberg, E., Lundberg, J. and Ekblom, B. Effects of dietary nitrate on oxygen cost during exercise. Acta physiologica 191(1): 59–66, 2007.
  3. Ignarro, L.J., Buga, G.M., Wood, K.S., Byrns, R.E. and Chaudhuri, G. Endothelium-derived relaxing factor produced and released from artery and vein is nitric oxide. Proceedings of the National Academy of Sciences of the United States of America 84(24): 9265–9269, 1987.
  4. Wylie, L.J., Kelly, J., Bailey, S.J., Blackwell, J.R., Skiba, P.F., Winyard, P.G., Jeukendrup, A.E., Vanhatalo, A. and Jones, A.M. Beetroot juice and exercise: pharmacodynamic and dose-response relationships. J Appl Physiol 115(3): 325–336, 2013.
  5. Dejam, A., Hunter, C.J., Schechter, A.N. and Gladwin, M.T. Emerging role of nitrite in human biology. Blood Cells, Molecules, and Diseases 32(3): 423–429, 2004.
  6. Jones, A.M. Dietary Nitrate: The New Magic Bullet? Gatorade Sports Science Exchange 26(110): 1–5, 2013.
  7. Lundberg, J.O., Weitzberg, E., Lundberg, J.M. and Alving, K. Intragastric nitric oxide production in humans: measurements in expelled air. Gut 35(11): 1543–1546, 1994.
  8. Benjamin, N., O’Driscoll, F., Dougall, H., Duncan, C., Smith, L., Golden, M. and Mckenzie, H. Stomach NO synthesis. Nature 368(6471): 502, 1994.
  9. Bailey, S.J., Vanhatalo, A., Winyard, P.G. and Jones, A.M. The nitrate-nitrite-nitric oxide pathway: Its role in human exercise physiology. European Journal of Sport Science 12(4): 309–320, 2012.
  10. Muggeridge, D.J., Howe, C.C., Spendiff, O., Pedlar, C., James, P.E. and Easton, C. A single dose of beetroot juice enhances cycling performance in simulated altitude. Med Sci Sports Exerc. 46(1): 143–150, 2014.
  11. Bailey, S.J., Winyard, P., Vanhatalo, A., Blackwell, J.R., Dimenna, F.J., Wilkerson, D.P., Tarr, J., Benjamin, N. and Jones, A.M. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol. 107(4): 1144–1155, 2009.
  12. Larsen, F.J., Schiffer, T.A., Borniquel, S., Sahlin, K., Ekblom, B., Lundberg, J.O. and Weitzberg, E. Dietary inorganic nitrate improves mitochondrial efficiency in humans. Cell Metabolism 13(2): 149–159, 2011.
  13. Lane, N. Power, sex, suicide: mitochondria and the meaning of life. Oxford University Press. 2005.
  14. Hoon, M.W., Johnson, N.A., Chapman, P.G. and Burke, L.M. The effect of nitrate supplementation on exercise performance in healthy individuals: a systematic review and meta-analysis. International Journal of Sport Nutrition & Exercise Metabolism 23(5):522–32, 2013.
  15. Murphy, M., Eliot, K., Heuertz, R.M. and Weiss, E. Whole beetroot consumption acutely improves running performance. Journal of the Academy of Nutrition and Dietetics 112(4): 548–552, 2012.
  16. Vanhatalo, A., Bailey, S.J., Blackwell, J.R., Dimenna, F.J., Pavey, T.G., Wilkerson, D.P., Benjamin, N., Winyard, P.G. and Jones, A.M. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology 299(4): R1121–31, 2010.
  17. examine.com, Nitrate. Available: http://www.examine.com/supplements/Nitrate/.
  18. Gilchrist, M., Winyard, P.G. and Benjamin, N. Dietary nitrate—Good or bad? Nitric Oxide 22(2): 104–109, 2010.
  19. Lansley, K.E., Winyard, P.G., Fulford, J., Vanhatalo, A., Bailey, S.J., Blackwell, J.R., Dimenna, F.J., Gilchrist, M., Benjamin, N. and Jones, A.M. Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study. J Appl Physiol. 110(3): 591–600, 2011.
  20. Lansley, K.E., Winyard, P.G., Bailey, S.J., Vanhatalo, A., Wilkerson, D.P., Blackwell, J.R., Gilchrist, M., Benjamin, N. and Jones, A.M. Acute dietary nitrate supplementation improves cycling time trial performance. Med Sci Sports Exerc. 43(6): 1125–1131, 2011.
  21. Wilkerson, D.P., Hayward, G.M., Bailey, S.J., Vanhatalo, A., Blackwell, J.R. and Jones, A.M. Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists. European Journal of Applied Physiology 112(12): 4127–4134, 2012.
  22. Engan, H.K., Jones, A.M., Ehrenberg, F. and Schagatay, E. Acute dietary nitrate supplementation improves dry static apnea performance. Respiratory physiology & Neurobiology 182(2): 53–59, 2012.
  23. Vanhatalo, A., Bailey, S.J., Blackwell, J.R., Dimenna, F.J., Pavey, T.G., Wilkerson, D.P., Benjamin, N., Winyard, P.G. and Jones, A.M. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology 299(4): R1121–31, 2010.
  24. Hopkins, W.G., Hawley, J.A. and Burke, L.M. Design and analysis of research on sport performance enhancement. Med Sci Sports Exec. 31(3): 472–485, 1999.
  25. Paton, C.D. and Hopkins, W.G. Variation in performance of elite cyclists from race to race. European Journal of Sport Science 6(01): 25–31, 2006.
  26. Gross, M., Baum, O. and Hoppeler, H. Antioxidant supplementation and endurance training: Win or loss? European Journal of Sport Science 11(1): 27–32, 2011.
  27. Hambridge, T. Nitrate and nitrite: intake assessment. In: WHO Food Additive Series. Vol. 50. Geneva (Switzerland): World Health Organization; 1053–1071, 2003.
  28. Webb, A.J., Patel, N., Loukogeorgakis, S., Okorie, M., Aboud, Z., Misra, S., Rashid, R., Miall, P., Deanfield, J., Benjamin, N., Macallister, R., Hobbs, A.J. and Ahluwalia, A. Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertension 51(3): 784–790, 2008.
  29. Govoni, M., Jansson, E.a., Weitzberg, E. and Lundberg, J.O. The increase in plasma nitrite after a dietary nitrate load is markedly attenuated by an antibacterial mouthwash. Nitric Oxide 19(4): 333–337, 2008.
  30. Cermak, N.M., Stinkens, R., Lundberg, J.O., Gibala, M.J. and Van Loon, L.J. No improvement in endurance performance after a single dose of beetroot juice. International Journal of Sport Nutrition & Exercise Metabolism 22(6): 470–478, 2012.