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No differences between beetroot juice and placebo on competitive 5-km running performance: A
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double-blind, placebo-controlled trial
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Philip Hurst1, Samantha Saunders2 and Damian Coleman1
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1School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, UK
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2 Human Performance, Defence Security Analysis Division, Defence Science and Technology
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Laboratory (DSTL), Porton Down, UK.
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Running head: Beetroot juice and competitive running performance
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Corresponding author
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Dr Philip Hurst
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School of Human and Life Sciences
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Canterbury Christ Church University
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Canterbury
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Kent, CT1 1QU
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United Kingdom
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Telephone +44 (0)1227 921466
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Email philip.hurst@canterbury.ac.uk
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Abstract
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We examined the effect of beetroot juice on endurance running performance in “real-world”
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competitive settings. One-hundred recreational runners (54% male; mean ± standard deviation, age =
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33.3 ± 12.3 years, training history = 11.9 ± 8.1 years, hours per week training = 5.9 ± 3.5) completed a
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quasi-randomised, double-blind, placebo-controlled study of 5-km competitive time-trials.
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Participants performed four trials separated by one week in the order of pre-baseline, two
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experimental, and one post-baseline. Experimental trials consisted of the administration of 70-mL
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nitrate rich beetroot juice (containing ~4.1 mmol of nitrate, Beet It Sport®) or nitrate depleted
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placebo (containing ~0.04 mmol of nitrate, Beet It Sport®) 2.5 hours prior to time-trials. Time to
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complete 5-km was recorded for each trial. No differences were shown between pre- and post-
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baseline (P = 0.128, CV = 2.66%). The average of these two trials is therefore used as baseline.
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Compared to baseline, participants ran faster with beetroot juice (mean differences = 22.2 ± 5.0 s, P <
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0.001, d = 0.08) and placebo (22.9 ± 4.5 s, P < 0.001, d = 0.09). No differences in times were shown
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between beetroot juice or placebo (0.8 ± 5.7 s, P < 0.875, d = 0.00). These results indicate that an
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acute dose of beetroot juice does not improve competitive 5-km time-trial performance in
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recreational runners compared to placebo.
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Keywords: dietary nitrate, ecological validity, ergogenic aids, nutrition, sport supplements
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Introduction
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Dietary nitrate supplementation increases plasma nitrate and nitrite via nitric oxide synthase
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independent pathway (Kapil et al., 2010) and has been shown to reduce blood pressure (Vanhatalo et
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al., 2010), adenosine triphosphate utilisation, phosphocreatine degradation (Bailey, Fulford, et al.,
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2010), the oxygen cost of submaximal exercise (Muggeridge et al., 2013; Wylie et al., 2016) and
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improve sport performance (Hoon et al., 2013; McMahon et al., 2017). In the last decade, there has
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been an exponential increase in research investigating the ergogenic effects of dietary nitrate rich
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products, such as beetroot juice (Hoon et al., 2013; Jones, 2014; McMahon et al., 2017).
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Dietary nitrate supplementation is a popular ergogenic aid amongst athletes of all abilities (Garthe &
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Maughan, 2018; Maughan et al., 2018). While a growing body of research has investigated the effects
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of dietary nitrate in elite athletes (Cermak, Gibala, et al., 2012; Cermak, Res, et al., 2012; Peeling et
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al., 2015), most research has sampled recreational cohorts (Hoon et al., 2013; McMahon et al., 2017).
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Bailey, Winyard, et al. (2010) examined the effects of dietary nitrate on time-to-exhaustion during
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graded step exercise in recreationally active participants (N = 7) and reported improvements of 16%
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compared to placebo. Similarly, Vanhatalo et al. (2010) reported that both acute (one day) and
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chronic (15 days) 0.5-L dietary nitrate supplementation improved steady-state V̇O2 during moderate-
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intensity exercise by ~4% in healthy participants (N = 8) and Jodra et al. (2020) showed that
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consumption of a 70-mL beetroot juice shot improved peak power-output during a Wingate test by
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4% in recreationally trained participants (N = 15).
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While data suggests dietary nitrate can improve sport performance (Hoon et al., 2013; Jones, 2014;
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McMahon et al., 2017), there are three limitations that characterise the literature. First, studies often
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assess performance in tightly controlled laboratories (Hoon et al., 2013; McMahon et al., 2017) and it
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is unknown whether the effects are similar in real-world competitive events. Second, testing often
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takes place in isolation with participants performing alone. It is well known that improvements in
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performance are shown during competition than exercising alone (Cooke et al., 2011; Corbett et al.,
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2012; Williams et al., 2015). It is therefore understandable to suggest that the beneficial effects of
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dietary nitrate and competition may not be additive and less marked during competition. Third,
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although studies may be sufficiently powered, two meta-analyses (Hoon et al., 2013; McMahon et al.,
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2017) report that studies investigating the effectiveness of dietary nitrate on sport performance often
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use small sample sizes (mean N = 11), which limit the detection of meaningful changes on
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performance (Burke & Peeling, 2018).
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Given the above, and to progress knowledge and understanding of the effectiveness of dietary nitrate
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on sport performance, we aimed to determine the effect of dietary nitrate in the form of beetroot
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juice on sport performance during a competitive time-trial using a sufficiently large sample. We used
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parkrun® as our time-trial event, which has shown to be a highly reliable measure of 5-km running
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performance (CV = 0.95%; Hurst & Board, 2017). Since 2004, parkrun has established weekly, free, 5-
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km running events that take place in more than 650 locations globally, with some events hosting over
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1000 runners (parkrun, 2020). We used a double-blind, quasi-randomised, placebo-controlled trial to
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investigate the effect of an acute dose of beetroot juice on time to complete a 5-km parkrun time-
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trial. We hypothesised that beetroot juice would improve time to complete 5-km compared to
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baseline and placebo.
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Methods
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The reporting of the current study followed the Proper Reporting of Evidence in Sport & Exercise
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Nutrition Trials (PRESENT) 2020 checklist (Betts et al., 2020).
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Participants
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One-hundred recreational runners were recruited to the study. Of these participants, 25 did not
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complete all trials and five reported injuries affecting their performance. These were removed leaving
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a final sample size of 70. Demographics for participants are shown in Table 1. A minimum sample size
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of 66 was calculated to detect a medium effect of beetroot juice on time to complete a 5-km time-
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trial. This sample was determined by power analysis using the G*Power v3.1 software (Faul et al.,
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2009), using a repeated measures ANOVA design, in which significance was set at 0.05, power (1-
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beta) at 95%, and given that effect sizes greater 0.2 are considered potentially beneficial for sport
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performance (Hopkins et al., 1999), the effect size (F) at 0.2.
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Inclusion criteria stipulated that participants had to be 18 years or over, passed a health questionnaire
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and have no indication of a physical injury. In addition, Hurst and Board (2017) reported that
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participants with greater familiarity of the parkrun course are more likely to improve test-retest
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reliability and reduce the coefficient variation (CV) of the performance measure. Thus, inclusion
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criteria stipulated that participants had completed two or more parkruns in the last four weeks and
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five or more in the preceding six months. The average number of parkruns participants performed at
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the time of recruitment was 24 ± 21.
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Design
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We used a within-participant, quasi-randomised, double-blind, placebo-controlled trial to determine
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the effects of an acute dose of beetroot juice on competitive 5-km running performance. Participants
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performed four trials separated by one week in the order of pre-baseline, two experimental, and one
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post-baseline. In experimental trials, participants were randomly allocated (1:1 ratio, no blocking or
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stratification) to receive beetroot juice or placebo using a computer-generator programme
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(www.randomization.org).
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Supplementation
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Participants consumed concentrated nitrate rich beetroot juice (containing ~4.1 mmol of nitrate; Beet
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it, James White Drinks Ltd., Ipswich, UK) and nitrate depleted beetroot juice (organic beetroot juice
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containing ~0.04 mmol of nitrate; Beet it, James White Drinks Ltd., Ipswich, UK). Pharmacokinetic data
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report that plasma nitrate peaks between 2.5 – 3 hours after ingestion of a single dose of beetroot
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juice (Webb et al., 2008), thus on the day of experimental trials, participants were instructed to
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consume 70-mL of the supplement 2.5 hours before the beginning of the trial. Both supplements
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were indistinguishable in taste and smell. Pilot testing with six participants not involved in the main
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study, were unable to identify which supplement had been ingested. The packaging of both
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supplements were identical in appearance, which were marked by a researcher with a unique code
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(i.e. “X” or “Y’) for random assignment. One researcher, who was not involved with any experimental
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testing, knew which codes corresponded to each supplement. To ensure that the placebo blind had
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been effective, a manipulation check was conducted after each experimental time-trial. Participants
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were asked to state what supplement they had received by selecting one of three options: 1)
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beetroot juice; 2) placebo and; 3) don’t know. Participants also indicated what time they had taken
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the shot, if any habitual practices in training and diet had changed leading up to the trial and if any
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other factors (e.g. motivation to perform the trial as fast as possible, weather conditions and injuries)
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affected their performance on the day of the trial.
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Procedure
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Ethical approval was granted by the lead author’s Institutional Ethics Committee (ref: 14/SAS/189)
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and parkrun’s Ethics Committee in accordance with the Declaration of Helsinki. Participants were
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recruited to the study in person and informed about the study’s aim, that participation was voluntary,
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and that all data collected would be used for research purposes only. After reading the information
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sheet and completing a health questionnaire, written informed consent was obtained.
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All trials were performed on a Saturday morning at 09:00 at the same location in Kent, United
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Kingdom between April and May 2015. Ambient conditions were recorded using publicly available
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data (https://www.wunderground.com/) collected by The Weather Company (IBM, Atlanta, Georgia,
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USA). Minimal differences were reported for all time-trials (temperature = 11.2 ± 1.8°C; humidity = 66
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± 4%; and windspeed = 14.6 ± 2 km/hr). Participants were instructed to keep exercise and nutritional
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habits the same, refrain from alcohol 24 hours preceding the trial, high intensity exercise 48-hours
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prior to the trials and requested not to consume other sport supplements not associated with the
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study. Participants were instructed to run the 5-km as fast as possible. Trials were performed
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alongside other runners not involved with the trial. Volunteer parkrun officials recorded completion
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times with data extracted from the official website at a later date (parkrun, 2020). Upon completion,
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participants reported to the research team who provided instructions for the next trial.
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Data analysis
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Time to complete 5-km for baseline trials were inputted into an online reliability spreadsheet to
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estimate reliability of pre- and post-baseline trials. Data was log transformed to reduce nonuniform
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errors and Pearson correlation (r), the intraclass correlation (ICC) and CV provided estimates of
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reliability. The r coefficient was interpreted as trivial (<0.1), small (0.3), moderate (0.5), large (0.7),
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nearly perfect (0.9) and perfect (1.0; Hopkins, 2015). The ICC was interpreted as low (0.20), moderate
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(0.50), high (0.75), very high (0.90) and extremely high (0.99; Hopkins, 2015). A paired samples t-test
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was conducted to determine systematic differences in performance between baseline trials.
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Data was analysed using SPSS version 24.0 (IBM, Armonk, NY) and tested for homogeneity of variance,
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normal distribution and outliers. Ratings of supplement assignment (correct, incorrect) were analysed
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using Chi-square (χ2). Cramer’s V was used as the effect size and interpreted as 0.10, 0.30 and 0.50,
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for a small, medium and large effect, respectively (Cohen, 2013). Repeated measures analysis of
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variance (ANOVA) was conducted to analyse effects of time between conditions. Greenhouse-Geisser
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epsilon was reported when sphericity was violated. Partial eta-squared (η2) is reported as the effect
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size, with values of 0.02, 0.13 and 0.26 indicating small, medium and large effects respectively
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(Cohen, 1992). Post-hoc Least Significant Difference (LSD) tests were used to examine differences
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between conditions and Cohen’s d (d) was calculated with values 0.2, 0.5 and 0.8 indicating small,
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medium and large effects, respectively (Cohen, 1992). Data is reported as means ± standard error of
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the mean (SEM) and 95% confidence intervals. Statistical significance was set at P <0.05.
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Results
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Preliminary analyses
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Times were similar between pre- and post-baseline (mean differences = 16.15 ± 1.47 s, 95% CI = -4.80
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to 37.10 s, P = 0.128, r = 0.95, ICC = 0.95, CV = 2.66%). The average of these two time-trials was thus
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used to measure baseline.
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Main analyses
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Results of χ2 tests indicated that participants did not accurately guess whether they were given
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beetroot juice or placebo (χ2 = 49.352, P = 0.457, Cramer’s V = 0.09). All participants reported to
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consume the supplement 2.5 hours before the start of the time-trial for each condition and none
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reported differences in training and nutritional routines leading up to the trials or factors affecting
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their performance (i.e. injuries, motivation and weather).
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Mean times for each condition are shown in figure 1. Repeated measures ANOVA revealed a
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significant effect for 5-km time between each condition (F2, 138 = 13.075, P < 0.001, η2 = 0.159).
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Compared to baseline, participants ran faster in the beetroot (mean differences = 22.2 ± 5.0 s, 95% CI
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= 12.2 to 32.1 s P < 0.001, d = 0.08) and placebo (22.9 ± 4.5 s, 95% CI = 13.9 to 32.0 s, P < 0.001, d =
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0.09) conditions. No differences in times were reported between beetroot and placebo (0.8 ± 5.7 s,
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95% CI = -10.6 to 12.1 s, P = 0.875, d = 0.00).
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Discussion
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This study was a first to use a double-blind, quasi-randomised, placebo-controlled trial to determine
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the effect of an acute dose of beetroot juice on competitive 5-km running performance in
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recreational runners. Our results indicate that compared to baseline, beetroot juice improves
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performance by on average 22.2 seconds (1.4%). However, when compared to a placebo,
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performance did not change, with mean differences reported at 0.8 seconds (0.05%). Collectively,
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results suggest that an acute does of beetroot juice does not improve 5-km performance in
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recreational runners.
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While meta-analyses report beneficial effects of beetroot juice on endurance performance (Hoon et
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al., 2013; McMahon et al., 2017), we found that beetroot juice does not improve time to complete a
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5-km time-trial. These results are similar to Cermak, Res, et al. (2012) and de Castro et al. (2019) who
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reported that compared to placebo, beetroot juice supplementation does not improve 1-hour cycling
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time-trial and time to complete 10-km running trial performance, respectively. More recent research
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(Jodra et al., 2020; Jonvik et al., 2018; Shannon et al., 2017) has reported that beetroot juice is more
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likely to affect shorter (e.g. 1500-m running) than longer distance (e.g. 10,000-m running) events.
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Shannon et al. (2017) suggest that dietary nitrate supplementation increases the recruitment of type
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II muscle fibres and augments blood flow and oxygen delivery. The increase in local blood flow is
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argued to decrease metabolic perturbations such as PCr degradation and adenosine diphosphate
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(ADP) accumulation (Vanhatalo et al., 2011), increase muscle force production and ultimately
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performance (Coggan et al., 2015). Thus, these effects are less likely to impact endurance
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performance. Given the results of our study, beetroot juice may have little effect on 5-km running
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time-trial performance.
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The null effects could also be explained by our main outcome variable. To help maximise the validity
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of our findings, we used an outdoor competitive 5-km time-trial. The physiological effects associated
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with beetroot juice may not influence performance as much during competitive time-trials than other
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factors (e.g. social comparisons, rewards for success and anxiety). While a 5-km parkrun may not
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produce the same psychophysiological response as the Olympics and World Championships, the
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results of our study are an important first step in identifying whether an acute dose of beetroot juice
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improves endurance performance in an ecological valid setting. Given that recreational runners
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arguably account for a substantial proportion of the consumer group for nutritional sport
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supplements (Maughan et al., 2018), our results highlight that the physiological effects of beetroot
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juice are unlikely to improve performance for this population. Instead, recreational runners should
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practice other methods that are more likely to benefit their performance in competitive settings (e.g.
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an improved training programme, nutritional strategy or psychological profile).
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It is important to consider the reliability of the performance measure when interpreting results. We
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reported improvements compared to baseline of 1.4% for both the beetroot juice and placebo
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condition. However, the CV of our measure was 2.66%. It is therefore likely that changes are
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attributable to systematic and random error. Similarly, the CV of our study is greater than previous
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research using a similar performance measure (CV = 0.95%; Hurst & Board, 2017). Reasons for the
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larger variance could be related to the time in-between baseline trials. Hurst and Board (2017)
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measured 5-km performance twice, separated by 1-week, whereas we separated baseline trials by 3-
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weeks. Although no differences were shown between baseline trials, it could be speculated that the
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greater time in-between trials increased the variance in our performance measure. This highlights the
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importance of measuring a further baseline time-trial after experimental trials to help identify
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systematic and random error of performance.
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While our performance measure is not as reliable as previous research (Hurst & Board, 2017), the
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performance measure still holds very good reliability (see Currell & Jeukendrup, 2008). Therefore, the
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results of our study are supported with high reliability and validity, and a large sample size. Generally,
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randomised controlled trials in sport and exercise employ small sample sizes and use outcome
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measurements in tightly controlled laboratories (Burke & Peeling, 2018). This approach can cause
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difficulties for researchers detecting meaningful changes in performance and translating the findings
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to applied practice. While challenges exist in recruiting adequate sample sizes and designing studies
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that are both reliable and valid, the results of this study highlight the opportunity for researchers to
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analyse the effects of interventions using a reliable and valid measure of running performance with a
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large sample. By using parkrun as our outcome measure, and recruiting a large sample, this study
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offers a clearer estimate of the true magnitude of changes in 5-km running performance after
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administration of an acute dose of beetroot juice.
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Limitations and future research
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While the study has a number of strengths relating to the study design, sample size and outcome
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measure, there were limitations. First, we measured the effect of a single acute dose of beetroot juice
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(70-mL). There is evidence to suggest that chronic supplementation of beetroot juice may be more
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beneficial for improving sport performance than acute supplementation (Jones, 2014; McMahon et
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al., 2017). Future research should aim to determine the effect of chronic beetroot juice
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supplementation on competitive 5-km running performance. Second, we did not control the content
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of nitrate rich foods (e.g. beetroot, lettuce and spinach) in participants’ diet. Those with a higher
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nitrate rich diet may show reduced effects with beetroot juice supplementation than those with a low
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nitrate rich diet (Jones, 2014; Jonvik et al., 2017). Prospective research should consider controlling for
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the impact of the consumption of nitrate rich diets in their results. Third, while we recruited a large
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sample size that were regular 5-km runners, they were not elite athletes. It is argued that the benefits
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of beetroot juice supplementation are more likely to be shown for highly-trained competitive athletes
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than recreational athletes due to the consequence of years of training adaptations and genetic factors
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(Burke & Peeling, 2018). Future research should aim to sample more highly trained athletes to further
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elucidate the effects of beetroot juice on competitive running performance. Fourth, given that our
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outcome measure does not mimic the atmosphere, pressure and demands that may be experienced
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during competitive events (e.g. national and international championships), and that athletes did not
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adjust their training to “peak” for each trial, the “competitive” element of our study is limited. It
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would be worthwhile to understand the effects of an acute dose of beetroot juice on running
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performance during more competitive events.
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Conclusion
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In conclusion, our results indicate that there is no difference in competitive 5-km time-trial
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performance when participants ingest an acute dose of beetroot juice or an equivalent placebo. This
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suggests that beetroot juice may not exert an ergogenic effect on 5-km running performance for
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recreational runners. The results of this study are supported with high reliability and validity using a
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large sample size. Future research studies should consider using other parkrun events to investigate
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the effectiveness of other sport interventions.
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Acknowledgments
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We would like to thank Dr Katrina Taylor for assistance in the study, parkrun® for granting access to
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recruit participants and data, and to the parkrun participants for their involvement in the study.
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Declarations
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Authors received no external funding for this research and declare no conflicts of interest.
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Authorships
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The study was designed by PH and SS; data were collected by PH and SS; data were analysed by PH;
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data interpretation and manuscript preparation were undertaken by PH, SS and DC. All authors
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approved the final version of the paper.
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J. P. (2017). Dietary nitrate supplementation enhances short but not longer duration running
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Dose-dependent effects of dietary nitrate on the oxygen cost of moderate-intensity exercise:
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Acute vs. chronic supplementation. Nitric Oxide, 57, 30-39.
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16
Table
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Table 1 Demographics of participants separated by gender
Male
Female
Overall
N
38
32
70
Age (years)
34.4 ± 11.6
32.1 ± 12.9
33.3 ± 12.3
Training history (years)
11.8 ± 7.0
11.9 ± 9.5
11.9 ± 8.1
Hours per week training
6.3 ± 3.9
5.5 ± 3.1
5.9 ± 3.5
Number of parkruns
21 ± 18
28 ± 24
24 ± 21
Personal best (minutes: seconds)
23:02 ± 4:42
29:05 ± 3:51
25:48 ± 5:16
Note: data are mean ± standard deviation
17
Figures
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412
Figure 1. Mean time to complete 5-km time-trials for each condition. Data are means ± SEM. * = P
413
<0.001 vs. beetroot and placebo.
414
