Impact of Dietary Nitrate Supplementation on Executive Function During Hypoxic Exercise.

We investigated the effects of 4-day dietary beetroot (BR) juice supplementation on executive function assessed by color-word Stroop task (CWST) in hypoxia (fraction of inspired oxygen [FiO2] = 0.1395). Eight healthy young men performed 25-minute leg cycling exercise (target heart rate, 140 bpm) randomly with placebo (PL) juice or BR supplementation. The CWST was evaluated at resting hypoxic condition (after 30 minutes of hypoxic exposure) and at 15 minutes during exercise. During exercise, the correct response time in the CWST was significantly shortened compared with those at rest with no differences between PL and BR. The response accuracy in the CWST with BR was marginally lower than that with PL during exercise (p = 0.066). There were no significant differences in all physiological values, including pulmonary ventilation, arterial oxygen saturation, partial pressure of end-tidal carbon dioxide output, and tissue oxygenation in the left frontal lobe, assessed by near-infrared spectroscopy during exercise conditions involving PL and BR supplementation. These results suggest that moderate exercise in hypoxia partially improved executive function; however, 4-day dietary BR supplementation did not improve executive function during hypoxic exercise.