Effects of Dietary Nitrate Supplementation on Physiological Responses, Cognitive Function, and Exercise Performance at Moderate and Very-High Simulated Altitude.

Purpose: Nitric oxide (NO) bioavailability is reduced during acute altitude exposure, contributing toward the decline in physiological and cognitive function in this environment. This study evaluated the effects of nitrate (NO₃^-) supplementation on NO bioavailability, physiological and cognitive function, and exercise performance at moderate and very-high simulated altitude. Methods: Ten males (mean (SD): VO_2max: 60.9 (10.1) ml·kg^-1·min^-1) rested and performed exercise twice at moderate (~14.0% O₂; ~3,000 m) and twice at very-high (~11.7% O₂; ~4,300 m) simulated altitude. Participants ingested either 140 ml concentrated NO₃^--rich (BRJ; ~12.5 mmol NO₃^-) or NO₃^--deplete (PLA; 0.01 mmol NO₃^-) beetroot juice 2 h before each trial. Participants rested for 45 min in normobaric hypoxia prior to completing an exercise task. Exercise comprised a 45 min walk at 30% VO₂max and a 3 km time-trial (TT), both conducted on a treadmill at a 10% gradient whilst carrying a 10 kg backpack to simulate altitude hiking. Plasma nitrite concentration ([NO₂^-]), peripheral oxygen saturation (SpO₂), pulmonary oxygen uptake (VO₂), muscle and cerebral oxygenation, and cognitive function were measured throughout. Results: Pre-exercise plasma [NO₂^-] was significantly elevated in BRJ compared with PLA (p = 0.001). Pulmonary VO₂ was reduced (p = 0.020), and SpO₂ was elevated (p=0.005) during steady-state exercise in BRJ compared with PLA, with similar effects at both altitudes. BRJ supplementation enhanced 3 km TT performance relative to PLA by 3.8%[1,653.9 (261.3) vs. 1718.7 (213.0) s] and 4.2%[1,809.8 (262.0) vs. 1,889.1 (203.9) s] at 3,000 and 4,300m, respectively (p = 0.019). Oxygenation of the gastrocnemius was elevated during the TT consequent to BRJ (p = 0.011). The number of false alarms during the Rapid Visual Information Processing Task tended to be lower with BRJ compared with PLA prior to altitude exposure (p = 0.056). Performance in all other cognitive tasks did not differ significantly between BRJ and PLA at any measurement point (p = 0.141). Conclusion: This study suggests that BRJ improves physiological function and exercise performance, but not cognitive function, at simulated moderate and very-high altitude. [ABSTRACT FROM AUTHOR]