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

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 (V̇o), 51 ± 6 ml·min·kg, 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 O 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]; = 0.03) compared with placebo. In addition, after 5-h hypoxia, nitrate increased sense of effort during submaximal exercise (∆7 [-1, 14]; = 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; = 0.07), sense of effort (∆14 [1, 28]; = 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 V̇o 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. 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.

Effects of dietary nitrate on respiratory physiology at high altitude - Results from the Xtreme Alps study

“…However, despite E NO increasing by 24% at a simulated altitude of 4300 m, there was no demonstrable benefit in isometric exercise performance, forearm blood flow or tissue oxygenation [39] . Meanwhile another study, which recently exposed 20 healthy volunteers to 6 h of 12% oxygen in a normobaric chamber, actually showed an increase in AMS scores (particularly headache) with dietary nitrate, contrasting our findings [61] . Inhaled NO has previously been shown to reduce pulmonary arterial pressures both at sea level and at altitude, offering particular benefit to HAPE-susceptible patients who tend to have high pulmonary artery pressures [11] , [12] .…”

Dietary nitrate supplementation effect on dynamic cerebral autoregulation in normoxia and acute hypoxia

“…The limited effects of dietary nitrate observed on dynamic CA in this study may be a consequence of the young healthy population recruited. Indeed, as other studies in young healthy individuals we report no effect of dietary nitrate on resting physiological responses in normoxia or hypoxia23,44,45 . Whether dietary nitrate influences cerebrovascular responses and dynamic CA in persons with reduced vascular function, poor NO bioavailability, or clinical populations with cerebrovascular disease remains to be investigated.…”

Impact of Dietary Nitrate Supplementation on Executive Function During Hypoxic Exercise

“…It was reported that a single bout of moderate-intensity exercise increased vessel diameter in vertebral arteries (i.e., vasodilation) compared with resting condition (Sato and Sadamoto, 2010), suggesting that headache may increase during exercise rather than at rest. A previous study have also reported that BR supplementations rather than PL caused more severe headache under hypoxic condition (Rossetti et al, 2017). Moreover, Lawley et al (2016) also demonstrated that only 10-minute exposure to severe hypoxia (FiO 2 = 0.11) could increase headache with intracranial pressure.…”