Caffeine and beetroot juice: are two supplements better than one?

Unlike many other sports nutrition supplements, caffeine – thanks to its ability to fight central nervous system fatigue – has been scientifically proven in numerous studies to enhance endurance performance, which explains why it has long been a popular supplement among endurance athletes. Nitrate (found naturally at high concentrations in some vegetables such as beetroot and kale) on the other hand is a much more recently investigated supplement that shows much promise. Nitrate appears to enhance blood flow through the fine capillaries of muscle tissue, helping to boost muscular efficiency during sub-maximal exercise, which in turn could prolong endurance. A question that naturally follows therefore is does combined caffeine/nitrate supplementation offer even better performance than just taking one alone? Although many athletes might resort to a combination on a ‘just in case’ basis,  a more scientific approach is to look at what the research says.

Caffeine beetroot juice combination

In one key study, the researchers examined the supplementation effects of dietary nitrate, caffeine, and their combination on 20km cycling time-trial performance in 14 competitive female cyclists [Journal of Strength and Conditioning Research: January 2015 – Volume 29 – Issue 1 – p 165–174]. The cyclists completed four separate 20km time-trials on a road bike fitted to a turbo-trainer. Two and a half hours before each trial, the subjects consumed one of the following:

  • A 70ml dose of beetroot juice with the nitrate content removed (placebo) plus (1 hour before) a caffeine placebo – ie a no, nitrate, no caffeine trial
  • A 70ml dose of concentrated beetroot juice containing 0.45g of dietary nitrate plus a caffeine placebo – ie a nitrate but no caffeine trial
  • A 70ml dose of beetroot juice with the nitrate content removed plus caffeine – ie a no nitrate plus caffeine trial
  • A 70ml dose of concentrated beetroot juice containing 0.45g of dietary nitrate plus caffeine – ie nitrate and caffeine (combination) trial

During each trial, the cyclists’ average power outputs were recorded along with heart rates and perceived ratings of exertion. The results were then compared across the four trials.

Caffeine rules

Analysis of the results showed that when the cyclists took the caffeine supplement (regardless or not of whether they’d taken nitrate) there was a significant boost to average power output in the time trial. Comparing caffeine supplementation to nitrate supplementation, cyclists averaged 205 watts when they took caffeine and 194 watts when they took nitrate. Significantly, the cyclists’ performances after nitrate supplementation were no better than placebo – ie it had zero performance-enhancing effect. How did the caffeine/nitrate combination affect the cyclists? It turned out that adding nitrate to caffeine yielded no extra benefits whatsoever over taking caffeine alone.

These results are consistent with those of another study carried out the previous year in which cyclists took caffeine, nitrate (in beetroot juice) or a combination of both before performing a cycling time trial [Appl Physiol Nutr Metab. 2014 Sep;39(9):1050-7]. In this study, subjects were 12 male and 12 female elite cyclist and they rode a course simulating the 2012 London Olympics course . Like the study above, the results showed a benefit in terms of performance of around 3.5% whenever caffeine was consumed, regardless of whether beetroot juice was consumed or not. And on its own, the beetroot juice produce no performance gains.

Practical implications for athletes

The first conclusion is that (unsurprisingly) caffeine supplementation was performance enhancing and that the nitrate (in the beetroot juice) was not. Why didn’t giving nitrate either alone or in addition provide any extra benefit? Well, the subjects in this study were highly trained competitive cyclists and research on both runners and cyclists indicates that for elites at least, nitrate may not be particularly effective(1,2). The reason for this may be because the muscles of elite endurance athletes are already so efficient in terms of blood blow that nitrate supplementation provides no additional benefit. Also, the researchers measured time trial performance – ie the cyclists’ flat out performance. But nitrate supplementation has only really been shown to help improve sub-maximal exercise performance, and this may be another reason why it failed to show benefits. The best advice for endurance athletes in the meantime is that caffeine is proven and can be a valuable performance enhancer. If you’re an elite athlete or are racing flat out, adding nitrate is unlikely to produce extra gains. However, for recreational athletes performing lower-intensity, long distance efforts, it still might be worth a try!


  1. Eur J Appl Physiol. 2012 Dec;112(12):4127-34
  2. Scand J Med Sci Sports. 2013 Feb;23(1):e21-31

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