Acute dietary nitrate supplementation improves arterial endothelial function at high altitude, A double-blinded randomized controlled cross over study
Authors: Emily Bakker, Harald Engan, Alexander Patrician, Erika Schagatay, Trine Karlsen, Ulrik Wisløff, Svein Erik Gaustad
DOI / Source: https://doi.org/10.1016/j.niox.2015.08.006
Date: 29 August 2015
Reading level: Intermediate
Why This Matters for Freedivers
Beetroot/nitrate supplements are popular in freediving circles, usually for “more nitric oxide” and better blood flow. This study gives a real-world clue that nitrate can quickly improve how well blood vessels respond under low-oxygen stress—so it’s a useful piece of evidence when you’re deciding whether supplements are just hype or could have a measurable effect. It also reminds you that “better blood flow” can be context-dependent: helpful in some situations, irrelevant in others.
Synopsis
At high altitude, many lowlanders get a double hit: less oxygen in the air and a vascular system that may not respond as smoothly as it does at home. One way researchers check “vessel health” is a test called flow-mediated dilation (FMD). In simple terms: you briefly restrict blood flow in the arm with a cuff, then release it and see how much the artery widens. A bigger, healthier widening response generally means the endothelium (the lining of the vessel) is doing its job well, largely through nitric oxide signaling.
This study asked a very practical question: can a single dose of dietary nitrate—delivered as beetroot juice—restore that vessel response at altitude?
Eleven healthy lowlanders took part in a trekking expedition in Nepal. The key experiment happened at 3700 m, using a randomized, double-blind, crossover design. On one day, participants drank a concentrated beetroot shot containing 5.0 mmol nitrate; on another day they drank a nitrate-depleted placebo shot that looked and tasted the same. They avoided things that could interfere with nitrate conversion (like mouthwash and tooth brushing) and then had FMD measured 3 hours later, when nitrate/nitrite effects are expected to be strongest.
Before trekking, they also measured FMD at 1370 m (baseline), and later they measured it again at 4200 m after several days at altitude, plus once more at 1370 m after returning from about four weeks of high-altitude exposure (with a short interruption where the group went down to 1370 m for two nights due to weather logistics).
The results were striking. Compared with baseline at 1370 m, FMD was clearly reduced at 3700 m after the placebo—meaning the arteries weren’t dilating as well in response to the same stimulus. But after beetroot juice, FMD bounced back toward baseline levels, essentially “normalizing” the response during that acute altitude exposure. In other words: altitude seemed to blunt endothelial function, and acute nitrate supplementation largely removed that blunting—at least for this short window.
Interestingly, beetroot juice did not noticeably change resting heart rate, oxygen saturation, or blood pressure in this field setting. So the main visible win here was specifically the vessel dilation response, not an obvious change in basic vital signs.
The longer-term picture was less rosy. In the subset who completed the longer stay, FMD remained lower at 4200 m and was still lower when measured back at 1370 m after the expedition. That suggests that altitude exposure can have lingering effects on endothelial function (at least for some time after return), and that one-time nitrate supplementation isn’t a “fix” for everything—it may be more like a useful tool for certain moments.
Overall, the study supports a simple idea: dietary nitrate can acutely improve peripheral vascular function during hypobaric hypoxia in lowlanders. It’s not freediving research, but it sits right on a topic freedivers care about—oxygen delivery and blood flow under hypoxic stress—and it provides a solid “yes, it can move the needle” example under real outdoor conditions.
Abstract
Introduction: Dietary nitrate supplementation serves as an exogenous source of nitrite and nitric oxide through the nitrate–nitrite–nitric oxide pathway, and may improve vascular functions during normoxia. The effects of nitrate supplementation in healthy lowlanders during hypobaric hypoxia are unknown.
Purpose: Determine the effect of acute oral nitrate supplementation via beetroot juice on endothelial function (flow mediated dilation; FMD) in lowlanders at 3700 m.
Methods: FMD was measured in the brachial artery of healthy subjects sojourning to high altitude. In a randomized, double-blinded crossover design, FMD was measured 3 h after beetroot juice (5.0 mmol nitrate) and placebo supplementation at 3700 m with a 24-h wash out period. FMD was also measured without 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), with an interruption by descent to lower altitude for two nights.
Results: FMD pre-trek was 6.53 ± 2.32% at 1370 m. At 3700 m, FMD was reduced to 3.84 ± 1.31% after placebo but was restored after beetroot juice to 5.77 ± 1.14%, similar to pre-trek levels. In those completing the longer altitude stay, FMD was lower at 4200 m and lower after return to 1370 m compared with pre-trek.
Conclusion: Acute dietary nitrate 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.