Acute dietary nitrate supplementation improves dry static apnea performance

Abstract: Acute dietary nitrate (NO3 −) supplementation has been reported to lower resting blood pressure, reduce the oxygen (O2) cost of sub-maximal exercise, and improve exercise tolerance. Given the proposed effects of NO3 − on tissue oxygenation and metabolic rate, it is possible that NO3 − supplementation might enhance the duration of resting apnea. If so, this might have important applications both in medicine and sport. We investigated the effects of acute NO3 − supplementation on pre-apnea blood pressure, apneic duration, and the heart rate (HR) and arterial O2 saturation (SaO2) responses to sub-maximal and maximal apneas in twelve well-trained apnea divers. Subjects were assigned in a randomized, double blind, crossover design to receive 70ml of beetroot juice (BR; containing ∼5.0mmol of nitrate) and placebo juice (PL; ∼0.003mmol of nitrate) treatments. At 2.5h post-ingestion, the subjects completed a series of two 2-min (sub-maximal) static apneas separated by 3min of rest, followed by a maximal effort apnea. Relative to PL, BR reduced resting mean arterial pressure by 2% (PL: 86±7 vs. BR: 84±6mmHg; P =0.04). The mean nadir for SaO2 after the two sub-maximal apneas was 97.2±1.6% in PL and 98.5±0.9% in BR (P =0.03) while the reduction in HR from baseline was not significantly different between PL and BR. Importantly, BR increased maximal apneic duration by 11% (PL: 250±58 vs. BR: 278±64s; P =0.04). In the longer maximal apneas in BR, the magnitude of the reductions in HR and SaO2 were greater than in PL (P ≤0.05). The results suggest that acute dietary NO3 − supplementation may increase apneic duration by reducing metabolic costs. [Copyright &y& Elsevier]