Acute dietary nitrate supplementation improves arterial endothelial function at high altitude: A double-blinded randomized controlled cross over study

• Endothelial function of lowlanders is reduced during long-term altitude exposure.
• Acute beetroot juice supplementation improves endothelial function at high altitude.
• Endothelial function of lowlanders is reduced at return to low altitude.

IntroductionDietary nitrate (NO3−) supplementation serves as an exogenous source of nitrite (NO2−) and nitric oxide (NO) through the NO3− – NO2− – NO pathway, and may improve vascular functions during normoxia. The effects of NO3− supplementation in healthy lowlanders during hypobaric hypoxia are unknown.PurposeDetermine the effect of acute oral NO3−supplementation via beetroot juice (BJ) on endothelial function (flow mediated dilation; FMD) in lowlanders at 3700 m.MethodsFMD was measured using ultrasound and Doppler in the brachial artery of 11 healthy subjects (4 females, age 25 ± 5 yrs; height 1.8 ± 0.1 m, weight 72 ± 10 kg) sojourning to high altitude. In a randomized, double-blinded crossover study design, FMD was measured 3 h after drinking BJ (5.0 mmol NO3−) and placebo (PL; 0.003 mmol NO3−) supplementation at 3700 m, with a 24-h wash out period between tests. FMD was also measured without any BJ supplementation pre-trek at 1370 m, after 5 days at 4200 m and upon return to 1370 m after 4 weeks of altitude exposure (above 2500 m). The altitude exposure was interrupted by a decent to lower altitude where subjects spent two nights at 1370 m before returning to altitude again.ResultsTen subjects completed the NO3− supplementation. FMD (mean ± SD) pre-trek value was 6.53 ± 2.32% at 1370 m. At 3700 m FMD was reduced to 3.84 ± 1.31% (p < 0.01) after PL supplementation but was normalized after receiving BJ (5.77 ± 1.14% (p = 1.00). Eight of the subjects completed the interrupted 4-week altitude stay, and their FMD was lower at 4200 m (FMD 3.04 ± 2.22%) and at post-altitude exposure to 1370 m (FMD 3.91 ± 2.58%) compared to pre-trek FMD at 1370 m.ConclusionAcute dietary NO3−supplementation may abolish altitude-induced reduction in endothelial function, and can serve as a dietary strategy to ensure peripheral vascular function in lowland subjects entering high altitude environments.