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


OBJECTIVE
Determine the effect of acute oral NO3-supplementation via beetroot juice (BJ) on endothelial function (flow mediated dilation; FMD) in lowlanders at 3700 m.


METHODS
FMD 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.


RESULTS
Ten 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.


CONCLUSIONS
Acute 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.
K.G. Jebsen Center of Exercise in Medicine at the Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Faculty of Medicine, Trondheim, Norway.
Emily
E
Bakker
Department of Health Sciences, Mid Sweden University, Östersund, Sweden; LHL-Klinikkene Røros, LHL-Health, Norway.
Harald
H
Engan
Department of Health Sciences, Mid Sweden University, Östersund, Sweden.
Alexander
A
Patrician
Department of Health Sciences, Mid Sweden University, Östersund, Sweden; Swedish Winter Sports Research Center, Mid Sweden University, Östersund, Sweden.
Erika
E
Schagatay
K.G. Jebsen Center of Exercise in Medicine at the Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Faculty of Medicine, Trondheim, Norway; St. Olav's University Hospital, Trondheim, Norway.
Trine
T
Karlsen
K.G. Jebsen Center of Exercise in Medicine at the Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Faculty of Medicine, Trondheim, Norway.
Ulrik
U
Wisløff
K.G. Jebsen Center of Exercise in Medicine at the Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Faculty of Medicine, Trondheim, Norway. Electronic address: Svein.e.gaustad@ntnu.no.
Svein Erik
SE
Gaustad
Altitude medicine; Beetroot juice; FMD; Field-study; Flow mediated dilation; Nepal; Nitric oxide