Dietary nitrate supplementation reduces the O₂cost of walking and running: a placebo-controlled study

Abstract

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.

Beetroot juice and exercise: pharmacodynamic and dose-response relationships

“…These findings are similar to the 14 -16% improvement in exercise tolerance reported previously following 5-6 days of BR supplementation at a lower dose (5-6 mmol NO 3 Ϫ ) (3,22). Although the mechanism(s) responsible for the ergogenic potential of NO 3 Ϫ supplementation remain uncertain, they are believed to be mediated via a biochemical reduction of ingested NO 3 Ϫ to biologically active NO 2 Ϫ and NO (4).…”

“…The same research group later reported a dose-dependent increase in plasma [NO 3 Ϫ ] and [NO 2 the above hemodynamic effects (3,26). Specifically, we (2,3,22) and others (6, 24 -26) have demonstrated that 3-6 days of dietary NO 3 Ϫ supplementation reduces the O 2 cost of moderateintensity exercise and may enhance exercise tolerance in healthy, young adults. It appears that these effects are related to NO 2 Ϫ or NO-mediated enhancements of muscle contractile function (2,17) and/or mitochondrial efficiency (24) and/or enhanced muscle blood flow, especially to type II fibers (14).…”

“…1B) (37) but is smaller than the 6% reduction reported 1 h postingestion of 0.033 mmol/kg BM sodium nitrate (25). In contrast to acute ingestion, longer-term BR supplementation (3-6 days at approximately 5-7 mmol NO 3 Ϫ /day) resulted in an approximate 5-7% reduction in steady-state V O 2 during moderate-intensity cycling (3,26) and running (22).…”

Nitrate pharmacokinetics: Taking note of the difference

“…Its application to modulate physiology and alleviate cardiovascular dysfunction shows particular promise in certain clinical conditions and patient cohorts, including reduction of mean arterial pressure in hypertension [1,2], effective quiescencing of platelet activation/aggregation [3], and reduce risk in conditions where tissue ischemia prevails [4]. However, it is the potential of oral NO 3 -to modify exercise/performance via elevation of plasma nitrite concentration ([NO 2 -]) that has been applied across a range of human test systems, from the effects of walking distance in a sedentary population [5] to enhancing performance in elite athletes [6].…”

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“…Nitric oxide becomes available in the body through oxidation of Larginine by the nitric oxide synthetases (NOS) (Alderton et al, 2001), but an additional pathway was recently unveiled, where NO becomes available through the sequential reduction of nitrate to nitrite and of nitrite to NO (Lundberg et al, 2008). As a result, inorganic nitrate from dietary sources emerges as a substrate for the in vivo generation of NO; indeed, dietary intake of nitrate produces the same effect as NO, namely vasoprotective activity, blood pressure reduction and additionally, decreases the whole body oxygen cost during exercise or enhanced maximal performance (Ferreira &Behnke, 2011;Lansley et al, 2011). The effects of nitrate can be achieved through consumption of large amount of vegetables which are nitrate-rich.…”