Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review
Authors: Raúl Domínguez, Eduardo Cuenca, José Luis Maté-Muñoz, Pablo García-Fernández, Noemí Serra-Paya, María Carmen Lozano Estevan, Pablo Veiga Herreros and Manuel Vicente Garnacho-Castaño
DOI / Source: https://doi.org/10.3390/nu9010043
Date: 6 January 2017
Reading level: Beginner
Why This Matters for Freedivers
If you do finswimming, dynamic apnea training, or any endurance-heavy freediving sessions, beetroot juice is one of the few supplements with some evidence for improving efficiency—doing the same work with slightly less oxygen cost. But freediving is not cycling: treat it as an experiment for training days (not “new supplement on a deep dive day”), and remember the basics from the review—timing (2–3 hours), dose, avoid antiseptic mouthwash, and watch caffeine interactions.
Synopsis
Beetroot juice is one of those “too simple to be real” supplements—just a vegetable drink—and yet athletes use it because it can boost nitric oxide (NO), a molecule that helps control blood flow and how efficiently muscles use oxygen. This paper is a systematic review that looked at research from 2010–2016 and selected 23 studies on athletes to answer a practical question: does beetroot juice actually improve cardiorespiratory endurance performance? 
Overall, the review suggests beetroot juice can help endurance performance mainly by improving efficiency—meaning athletes sometimes use less oxygen (lower VO₂) for the same effort, or they can hold a given pace longer. Across different sports (cycling, running, kayaking, swimming), some studies showed faster time trials or longer time-to-exhaustion at submaximal intensities. But it’s not a miracle and it’s not consistent: some studies show no benefit, and results seem to depend on things like the athlete’s training level, the test type, and crucially timing and dose. 
The review also gives very usable “how to” details. It notes that peak blood nitrite (the step that leads to NO) tends to occur about 2–3 hours after ingestion, and many effective protocols used around 6–8 mmol nitrate (sometimes more in high-level athletes). It also highlights two common “gotchas”: antibacterial mouthwash can reduce the nitrate→nitrite conversion in the mouth (so it can blunt the effect), and combining beetroot with caffeine doesn’t reliably add benefits and may even interfere in some contexts. On hypoxia/altitude, the review says evidence is mixed: there are hints it might reduce the performance hit of hypoxia in some cases, but it’s not settled.
Abstract
Athletes use nutritional supplementation to enhance the effects of training and achieve improvements in their athletic performance. Beetroot juice increases levels of nitric oxide (NO), which serves multiple functions related to increased blood flow, gas exchange, mitochondrial biogenesis and efficiency, and strengthening of muscle contraction. These biomarker improvements indicate that supplementation with beetroot juice could have ergogenic effects on cardiorespiratory endurance that would benefit athletic performance. The aim of this literature review was to determine the effects of beetroot juice supplementation and the combination of beetroot juice with other supplements on cardiorespiratory endurance in athletes. A keyword search of DialNet, MedLine, PubMed, Scopus and Web of Science databases covered publications from 2010 to 2016. After excluding reviews/meta-analyses, animal studies, inaccessible full-text, and studies that did not supplement with beetroot juice and adequately assess cardiorespiratory endurance, 23 articles were selected for analysis. The available results suggest that supplementation with beetroot juice can improve cardiorespiratory endurance in athletes by increasing efficiency, which improves performance at various distances, increases time to exhaustion at submaximal intensities, and may improve the cardiorespiratory performance at anaerobic threshold intensities and maximum oxygen uptake (VO2max). Although the literature shows contradictory data, the findings of other studies lead us to hypothesize that supplementing with beetroot juice could mitigate the ergolytic effects of hypoxia on cardiorespiratory endurance in athletes. It cannot be stated that the combination of beetroot juice with other supplements has a positive or negative effect on cardiorespiratory endurance, but it is possible that the effects of supplementation with beetroot juice can be undermined by interaction with other supplements such as caffeine.