Dietary nitrate supplementation increases acute mountain sickness severity and sense of effort during hypoxic exercise.

Journal of applied physiology

Oct 2017

DOI: 10.1152/japplphysiol.00293.2017

Citations:26

Influential Citations:1

Interventional (Human) Studies

Enhanced Details

Methods

Twenty recreationally-active men; age 22 ± 4 years; VO2max 51 ± 6 mL·kg-1·min-1. Randomized double-blind placebo-controlled crossover. Baseline normoxic and hypoxic maximal tests; six-day supplementation periods with washout; 6-hour hypoxic exposure (FiO2 0.124) on day five; time-to-exhaustion test on day six.

Intervention

Daily nitrate-rich beetroot juice (70 mL; ~6.4 mmol NO3-) vs nitrate-depleted placebo (70 mL; ~0.003 mmol NO3-); ingested 2.5 hours before tests; duration: six days.

Results

Nitrate increased plasma NO metabolites but did not reduce AMS or improve overall exercise performance. During 4–6 hours of hypoxia, nitrate increased headache severity by about 10 mm on a 0–100 mm scale (p=0.03) and tended to raise AMS-C (p=0.07). In AMS− participants, nitrate had no effect on headache or AMS-C but reduced ventilation during one submaximal bout (p=0.03). In AMS+ participants, nitrate increased headache severity by ~26 mm (p=0.07), raised ventilation, VO2, and mean arterial pressure during submaximal exercise, and increased sense of effort (p=0.04). Time-to-exhaustion in acute hypoxia did not improve with nitrate. Overall, nitrate increases AMS symptoms and perceived effort, especially in those who develop AMS, and is not recommended as an AMS prophylactic or ergogenic aid for non-acclimatized individuals at altitude.

Limitations

Male-only sample; small AMS+ subgroup; short 6-hour hypoxic exposure; potential carryover despite washout; no direct measurement of cerebral blood flow; subjective AMS assessment; limited generalizability.

Abstract

Dietary nitrate supplementation enhances sea level performance and may ameliorate hypoxemia at high altitude. However, nitrate may exacerbate acute mountain sickness (AMS), specifically headache. This study investigated the effect of nitrate supplementation on AMS symptoms and exercise responses with 6-h hypoxia. Twenty recreationally active men [age, 22 ± 4 yr, maximal oxygen consumption (V̇o2max), 51 ± 6 ml·min-1·kg-1, means ± SD] completed this randomized double-blinded placebo-controlled crossover study. Twelve participants were classified as AMS- on the basis of Environmental Symptoms Questionnaire [Acute Cerebral Mountain Sickness score (AMS-C)] <0.7 in both trials, and five participants were classified as AMS+ on the basis of AMS-C ≥0.7 on placebo. Five days of nitrate supplementation (70-ml beetroot juice containing ~6.4 mmol nitrate daily) increased plasma NO metabolites by 182 µM compared with placebo but did not reduce AMS or improve exercise performance. After 4-h hypoxia [inspired O2 fraction ([Formula: see text]) = 0.124], nitrate increased AMS-C and headache severity (visual analog scale; whole sample ∆10 [1, 20] mm, mean difference [95% confidence interval]; P = 0.03) compared with placebo. In addition, after 5-h hypoxia, nitrate increased sense of effort during submaximal exercise (∆7 [-1, 14]; P = 0.07). In AMS-, nitrate did not alter headache or sense of effort. In contrast, in AMS+, nitrate increased headache severity (∆26 [-3, 56] mm; P = 0.07), sense of effort (∆14 [1, 28]; P = 0.04), oxygen consumption, ventilation, and mean arterial pressure during submaximal exercise. On the next day, in a separate acute hypoxic exercise test ([Formula: see text] = 0.141), nitrate did not improve time to exhaustion at 80% hypoxic V̇o2max In conclusion, dietary nitrate increases AMS and sense of effort during exercise, particularly in those who experience AMS. Dietary nitrate is therefore not recommended as an AMS prophylactic or ergogenic aid in nonacclimatized individuals at altitude.NEW & NOTEWORTHY This is the first study to identify that the popular dietary nitrate supplement (beetroot) does not reduce acute mountain sickness (AMS) or improve exercise performance during 6-h hypoxia. The consumption of nitrate in those susceptible to AMS exacerbates AMS symptoms (headache) and sense of effort and raises oxygen cost, ventilation, and blood pressure during walking exercise in 6-h hypoxia. These data question the suitability of nitrate supplementation during altitude travel in nonacclimatized people. show less