Recent study results don't correspond with this view and found that dietary nitrate intake has potential health benefits. Until we know more about the potential risks, it's recommended that athletes consume natural products that are rich in nitrates rather than pharmacological products.
Green leafy vegetables and beetroot increase the availability of nitric oxide
In your body nitrates are converted into nitrite and eventually into nitric oxide (NO). In human physiology is nitric oxide important because it changes processes that are essential to exercise performance. Recent evidence indicates that an increased availability of nitric oxide lowers blood pressure, enhances muscle efficiency, and may enhance performance.
The concentration of nitrate and nitrite in your body can be increased by dietary means. Therefore, dietary nitrate supplementation is a practically method to increase the availability of nitric oxide. Green leafy vegetables such as lettuce, spinach, rocket, celery, and beetroot are a great source of inorganic nitrate, but nitrate content can vary according to soil conditions, time of the year and storage.
Table 1. Nitrate content of vegetables (mg/100 gram fresh weight)
|> 250 mg||Lettuce, spinach, rocket, celery, beetroot, cress, and chervil|
|100-250 mg||Celeriac, fennel, leek, endive, and parsley|
|50-100 mg||Cabbage, turnip, dill, and savoy cabbage|
|20-50 mg||Carrot, cauliflower, cucumber, broccoli, and pumpkin|
|<20 mg||Aspargus, mushroom, pea, aubergine, onion, pepper, potato, sweet potato, and tomato|
How much nitrate is needed?
After consuming about 300-400 mg dietary nitrate, nitrite level peaks within 2-3 hours and remains elevated for a further 6 to 8 hours10. Therefore, it is recommended to consume nitrate about 3 hours prior to training or competition. A daily dose of 300-400 mg nitrate is required to maintain a high nitrite level . Although 300-400 mg of nitrate seems to be effective, researchers are still investigating what the most effective dose-response is. At the moment it is unclear what the influence of sustained supplementation on training adaptation is because nitrate also has antioxidant properties that could blunt adaptations to training.
Beetroot juice is well known for its performance benefits. However, no improvements in performance were found when subjects were supplemented with a placebo beetroot juice that had been depleted of nitrate6. This means that nitrate is the most important ingredient of beetroot juice responsible for performance benefits. So it's not only beetroot juice that can improve your performance. Table 1 shows the nitrate content of some other vegetables. A daily portion of most fresh vegetables, about 200 grams, is already enough to have an adequate supply of nitrate.
Nitrate supplementation can improve performance by 1-2%
After nitrate supplementation are blood lactate levels during exercise not higher while the oxygen cost of exercise is lower1 7. This suggests that there is no compensatory increase in anaerobic energy production as might be expected when aerobic energy production would be lower. So, nitrate supplementation results in an improved efficiency. A lower oxygen consumption at the same intensity could result from a lower energy cost of muscle contraction for the same amount of work (improved muscle efficiency), or a lower oxygen cost for the same rate of energy production (improved mitochondrial efficiency).
Several researchers reported that nitrate supplementation significantly reduces VO2 at two sub-maximal work rates, improved mean power output, and time trial performance by 1-2% in trained cyclists1 3 5 7. While nitrate supplementation seems to improve maximal performance of 5-25 minutes, there is no evidence that it also improves short high-intensity, intermittent-intensity, and long term endurance performance.
Highly trained athletes seem less sensitive to nitrate supplementation
Most of the published studies have involved recreational or moderately trained athletes, it's not clear whether nitrate supplementation has performance enhancing effects on highly trained or elite athletes. There are several possible explanations for this. One of them is that resting Nitric Oxide levels are higher in elite athletes, this reduces the scope for nitrate supplementation or they may require larger nitrate doses to change resting Nitric Oxide levels4 8.
Early studies tried to increase the amount of Nitric Oxide in the blood by supplementing with the amino acid L-arginine2 9. The conversion of L-arginine to Nitric oxide in blood only occurs when enough oxygen is available, which is not the case during exercise. So, it's also possible that elite athletes produce more Nitric Oxide from the oxidation of L-arginine and are less dependent on Nitric Oxide production from nitrate. Besides that, they have greater mitochondrial and capillary density which limits the development of hypoxia and acidosis during exercise, which preserves the production of Nitric Oxide from L-arginine oxidation.
1. Bailey, S. J., Winyard, P., Vanhatalo, A., Blackwell, J. R., Dimenna, F. J., Wilkerson, D. P., et al. (2009). Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. Journal of Applied Physiology , 107(4):1144-55.
2. Boucher, J. L., Moali, C., & Tenu, J. P. (1999). Nitric oxide biosynthesis, nitric oxide synthase inhibitors and arginase competition for L-arginine utilization. Cellular and Molecular Life Sciences , Jul;55(8-9):1015-28.
3. Cermak, N. M., Gibala, M. J., & van Loon, L. J. (2012). Nitrate supplementation's improvement of 10-km time-trial performance in trained cyclists. International Journal of Sport Nutrition and Exercise Metabolism. , 22(1):64-71.
4. Jungersten, L., Ambring, A., & Wennalm, A. (1997). Both physical fitness and acute exercise regulate nitric oxide formation in healthy humans. Journal of Applied Physiology , 82(3):760-4.
5. Lansley, K. E., Winyard, P. G., Bailey, S. J., Vanhatalo, A., Wilkerson, D. P., Blackwell, J. R., et al. (2011b). Acute dietary nitrate supplementation improves cycling time trial performance. Medicine and Science in Sports and Exercise. , 43(6):1125-31.
6. Lansley, K. E., Winyard, P. G., Fulford, J., Vanhatalo, A., Bailey, S. J., Blackwell, J. R., et al. (2011a). Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study. Journal of Applied Physiology , 110(3):591-600.
7. Larsen, F. J., Weitzberg, E., Lundberg, J., & Ekblom, B. (2007). Effects of dietary nitrate on oxygen cost during exercise. Acta physiologica , 191(1):59-66.
8. Schena, F., Cuzzolin, L., Pasetto, M., & Benoni, G. (2002). Plasma nitrite/nitrate and erythropoietin levels in cross-country skiers during altitude training. Journal of Sport Medicine and Physical Fitness , Jun;42(2):129-34.
9. Vanhatalo, A., Bailey, S. J., DiMenna, F. J., Blackwell, J. R., Wallis, G. A., & Jones, A. M. (2013). No effect of acute L-arginine supplementation on O₂ cost or exercise tolerance. European Journal of Applied Physiology , 113(7):1805-19.
10. Webb, A. J., Patel, A., Loukogeorgakis, S., Okorie, M., Aboud, Z., Misra, S., et al. (2008). Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertension , 51(3):784-90.