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Effects of dietary nitrate on oxygen cost during exercise
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.ORCID iD: 0000-0002-1343-8656
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.ORCID iD: 0000-0002-4030-5437
2007 (English)In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 191, no 1, 59-66 p.Article in journal (Refereed) Published
Abstract [en]

AIM: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO(3) (-)) and nitrite (NO(2) (-)). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise. METHOD: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg(-1) day-1) or an equal amount of sodium chloride (placebo). RESULTS: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo(2) decreased from 2.98 +/- 0.57 during CON to 2.82 +/- 0.58 L min(-1) during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 +/- 1.6 during CON to 21.1 +/- 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo(2) or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates. CONCLUSION: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.

Place, publisher, year, edition, pages
2007. Vol. 191, no 1, 59-66 p.
National Category
Physiology
Identifiers
URN: urn:nbn:se:gih:diva-302OAI: oai:DiVA.org:gih-302DiVA: diva2:662
Available from: 2007-10-12 Created: 2007-10-12 Last updated: 2017-03-31Bibliographically approved
In thesis
1. Dietary inorganic nitrate: role in exercise physiology, cardiovascular and metabolic regulation
Open this publication in new window or tab >>Dietary inorganic nitrate: role in exercise physiology, cardiovascular and metabolic regulation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nitric oxide (NO) is a ubiquitous signaling molecule with a vast number of tasks in the body, including regulation of cardiovascular and metabolic function. A decreased bioavailability of NO is a central event in disorders such as hypertension and metabolic syndrome. NO is also important in the regulation of blood flow and metabolism during exercise. The production of NO has previously been thought to be under the exclusive control of the nitric oxide synthases (NOS) but this view is now being seriously challenged. Recent lines of research suggest the existence of an NO-synthase independent pathway in which the supposedly inert NO oxidation products nitrate (NO3-) and nitrite (NO2-) can be reduced back to NO in blood and tissues. An important additional source of nitrate is our everyday diet and certain vegetables are particularly rich in this anion. In this thesis the possibility that dietary derived nitrate is metabolized in vivo to form reactive nitrogen oxides with NO-like bioactivity has been explored. It is shown that nitrate in amounts easily achieved via the diet, increases the systemic levels of nitrite and reduces blood pressure in healthy humans. Moreover, nitrate reduces whole body oxygen cost during submaximal and maximal exercise; a surprising effect involving improvement in mitochondrial efficiency and reduced expression of specific mitochondrial proteins regulating proton conductance. Alterations in the mitochondrial affinity for oxygen can explain this reduction in both submaximal and maximal oxygen consumption and predicts basal metabolic rate in humans. Finally, in mice lacking endothelial NO synthase, dietary supplementation with nitrate could reverse several features of the metabolic syndrome that develop in these animals. These studies demonstrate that dietary nitrate can fuel a nitrate-nitrite-NO pathway with important implications for cardiovascular and metabolic functions in health and disease.

Place, publisher, year, edition, pages
Solna: Karolinska Institutet, 2011
National Category
Medical and Health Sciences
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-2079 (URN)978-91-7457-397-8 (ISBN)
Public defence
2011-06-17, Aulan Farmakologen, Nanna Svartz väg 2, Solna, 09:00 (English)
Opponent
Supervisors
Note
Avhandling vid Karolinska Institutet och Gymnastik- och idrottshögskolan, GIHAvailable from: 2012-01-09 Created: 2012-01-09 Last updated: 2016-08-08Bibliographically approved

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