Dietary nitrate supplementation reduces the O 2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans

• Published in: Journal of applied physiology (1985) 2009-10, Vol.107 (4), p.1144-1155
• Main Authors: Bailey, Stephen J., Winyard, Paul, Vanhatalo, Anni, Blackwell, Jamie R., DiMenna, Fred J., Wilkerson, Daryl P., Tarr, Joanna, Benjamin, Nigel, Jones, Andrew M.
• Format: Article
• Language: English
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00722.2009

Pharmacological sodium nitrate supplementation has been reported to reduce the O 2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O 2 cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19–38 yr) consumed 500 ml/day of either BR (containing 11.2 ± 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of “step” moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4–6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 ± 44 vs. PL: 140 ± 50 nM; P < 0.05), and systolic blood pressure was significantly reduced (BR: 124 ± 2 vs. PL: 132 ± 5 mmHg; P < 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O 2 extraction (as estimated using near-infrared spectroscopy). The gain of the increase in pulmonary O 2 uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 ± 0.7 vs. PL: 10.8 ± 1.6 ml·min −1 ·W −1 ; P < 0.05). During severe exercise, the O 2 uptake slow component was reduced (BR: 0.57 ± 0.20 vs. PL: 0.74 ± 0.24 l/min; P < 0.05), and the time-to-exhaustion was extended (BR: 675 ± 203 vs. PL: 583 ± 145 s; P < 0.05). The reduced O 2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans.