Dietary Nitrate Supplementation Does Not Alter Exercise Efficiency at High Altitude – Further Results From the Xtreme Alps Study

Hennis, Philip J., Cumpstey, Andrew F., O'Doherty, Alasdair, Fernandez, Bernadette O., Gilbert-Kawai, Edward T., Mitchell, Kay, Moyses, Helen, Cobb, Alexandra, Meale, Paula, Pöhnl, Helmut, Mythen, Monty G., Grocott, Michael P. W., Levett, Denny Z. H., Martin, Daniel S., Feelisch, Martin and Xtreme Alps research group, (2022) Dietary Nitrate Supplementation Does Not Alter Exercise Efficiency at High Altitude – Further Results From the Xtreme Alps Study. Frontiers in Physiology, 13. p. 827235. ISSN 1664-042X

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Introduction: Nitrate supplementation in the form of beetroot juice (BRJ) ingestion has been shown to improve exercise tolerance during acute hypoxia, but its effect on exercise physiology remains unstudied during sustained terrestrial high altitude exposure. We hypothesised that performing exercise at high altitude would lower circulating nitrate and nitrite levels and that BRJ ingestion would reverse this phenomenon while concomitantly improving key determinants of aerobic exercise performance. Methods: Twenty seven healthy volunteers (21 male) underwent a series of exercise tests at sea level (SL, London, 75 m) and again after 5-8 days at high altitude (HA, Capanna Regina Margherita or ‘Margherita Hut’, 4559 m). Using a double-blind protocol, participants were randomised to consume a beetroot/fruit juice beverage (3 doses per day) with high levels of nitrate (~0.18 mmol/kg/day) or a nitrate-depleted placebo (~11.5 μmoles/kg/day) control drink, from 3 days prior to the exercise trials until completion. Submaximal constant work rate cycle tests were performed to determine exercise efficiency and a maximal incremental ramp exercise test was undertaken to measure aerobic capacity, using breath-by-breath pulmonary gas exchange measurements throughout. Concentrations of nitrate, nitrite and nitrosation products were quantified in plasma samples collected at 5 timepoints during the constant work rate tests. Linear mixed modelling was used to analyse data.Results: At both SL & HA, plasma nitrate concentrations were elevated in the nitrate supplementation group compared to placebo (P<0.001) but did not change throughout increasing exercise work rate. Delta exercise efficiency was not altered by altitude exposure (P=0.072) or nitrate supplementation (P=0.836). \.VO2peak decreased by 24 at high altitude (P<0.001) and was lower in the nitrate-supplemented group at both sea level and high altitude compared to placebo (P=0.041). Dietary nitrate supplementation did not alter other peak exercise variables or oxygen consumption at anaerobic threshold. Circulating nitrite and S-nitrosothiol levels unexpectedly rose in a few individuals right after cessation of exercise at high altitude.Conclusion: Whilst regularly consumed during an 8 day expedition to terrestrial high altitude, nitrate supplementation did not alter exercise efficiency and other exercise physiological variables, except decreasing \.VO2peak. These results and those of others question the practical utility of BRJ consumption during prolonged altitude exposure.

Item Type: Article
Additional Information: Funding information: Xtreme Alps received charitable support from the Friends of University College Hospital NHS Foundation Trust as well as unrestricted research funding from Smiths Medical Ltd. and Deltex Medical Ltd. MF acknowledges support from the Faculty of Medicine, University of Southampton. Part of the work carried out at the University of Warwick was supported by funds from the Medical Research Council (Strategic Appointment Scheme, to MF). None of the funding bodies or the institutions the authors are affiliated with had any role in the study design; collection, analysis, and interpretation of data; manuscript preparation; or decision to publish. AFC was funded by the National Institute for Health Research Southampton Biomedical Research Centre and also received funding as a National Institute for Health Research Academic Clinical Fellow. KM is a National Institute for Health Research (NIHR) Senior Nurse and Midwife Research Leader. Neither of these funders was involved in study design, collection, analysis, interpretation of data, writing of this article, or decision to submit it for publication.
Uncontrolled Keywords: Exercise, high altitude, hypoxia, nitric oxide, Beetroot, nitrite
Subjects: B400 Nutrition
C600 Sports Science
Department: Faculties > Health and Life Sciences > Sport, Exercise and Rehabilitation
Depositing User: John Coen
Date Deposited: 20 Jan 2022 15:01
Last Modified: 04 Mar 2022 15:30

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