Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study.
Dietary supplementation with beetroot juice (BR) has been shown to reduce resting blood pressure and the O(2) cost of submaximal exercise and to increase tolerance to high-intensity cycling. We tested the hypothesis that the physiological effects of BR were consequent to its high NO(3)(-) content per se, and not the presence of other potentially bioactive compounds. We investigated changes in blood pressure, mitochondrial oxidative capacity (Q(max)), and physiological responses to walking and moderate- and severe-intensity running following dietary supplementation with BR and NO(3)(-)-depleted BR [placebo (PL)]. After control (nonsupplemented) tests, nine healthy, physically active male subjects were assigned in a randomized, double-blind, crossover design to receive BR (0.5 l/day, containing ∼6.2 mmol of NO(3)(-)) and PL (0.5 l/day, containing ∼0.003 mmol of NO(3)(-)) for 6 days. Subjects completed treadmill exercise tests on days 4 and 5 and knee-extension exercise tests for estimation of Q(max) (using (31)P-magnetic resonance spectroscopy) on day 6 of the supplementation periods. Relative to PL, BR elevated plasma NO(2)(-) concentration (183 ± 119 vs. 373 ± 211 nM, P < 0.05) and reduced systolic blood pressure (129 ± 9 vs. 124 ± 10 mmHg, P < 0.01). Q(max) was not different between PL and BR (0.93 ± 0.05 and 1.05 ± 0.22 mM/s, respectively). The O(2) cost of walking (0.87 ± 0.12 and 0.70 ± 0.10 l/min in PL and BR, respectively, P < 0.01), moderate-intensity running (2.26 ± 0.27 and 2.10 ± 0.28 l/min in PL and BR, respectively, P < 0.01), and severe-intensity running (end-exercise O(2) uptake = 3.77 ± 0.57 and 3.50 ± 0.62 l/min in PL and BL, respectively, P < 0.01) was reduced by BR, and time to exhaustion during severe-intensity running was increased by 15% (7.6 ± 1.5 and 8.7 ± 1.8 min in PL and BR, respectively, P < 0.01). In contrast, relative to control, PL supplementation did not alter plasma NO(2)(-) concentration, blood pressure, or the physiological responses to exercise. These results indicate that the positive effects of 6 days of BR supplementation on the physiological responses to exercise can be ascribed to the high NO(3)(-) content per se.
School of Sport and Health Sciences, St. Luke's Campus, Univ. of Exeter, Heavitree Rd., Exeter EX1 2LU, UK.
Katherine E
KE
Lansley
Paul G
PG
Winyard
Jonathan
J
Fulford
Anni
A
Vanhatalo
Stephen J
SJ
Bailey
Jamie R
JR
Blackwell
Fred J
FJ
DiMenna
Mark
M
Gilchrist
Nigel
N
Benjamin
Andrew M
AM
Jones
D000284:Administration, Oral; D027461:Beta vulgaris / Q000737:chemistry*; D001628:Beverages; D019587:Dietary Supplements; D005684:Gait / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D009566:Nitrates / Q000008:administration & dosage*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D010936:Plant Extracts / Q000008:administration & dosage*; D012420:Running / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult
D009566:Nitrates; D010936:Plant Extracts