Beet Juice and Cognitive Performance

Exercise, if it’s long and hard enough, makes you stupider. Or, to be more precise, “during high-intensity exercise, cognitive abilities diminish and mental fatigue develops” – an effect you can pick up by measuring reaction times. This is particularly relevant for athletes in skill sports, who have to make split-second decisions late in games (though, as anyone who has ever taken a wrong turn or miscounted laps late in a race knows, it can also be relevant in endurance sports).

A recent study by Andrew Jones’s group at the University of Exeter, published in the European Journal of Applied Physiology, takes beet juice research in an interesting new direction. In a double-blind crossover study, they put 16 team-sport players (field hockey, soccer, rugby) through an intermittent sprint protocol designed to simulate the demands of a match: two 40-minute halves consisting primarily of two-minute blocks of 6-second all-out sprints, 100 seconds of active recovery, and 14 seconds of rest, all performed on a stationary bike. During each active recovery period, the subjects had to perform a series of cognitive tests – pressing specific buttons in response to combinations of arrows, colours, or words – with accuracy and reaction time measured. Each subject did this twice, once after seven days of drinking beet juice (one 70 mL shot every morning and evening, two shots on the morning of the test 2.5 hours prior), and another time after seven days of drinking plcaebo beet juice with the nitrate (the active ingredient) filtered out.

There are a number of interesting results from the study, including the fact that the athletes managed to perform ~3.5 percent more total work during the sprints when they’d had beet juice. The usual explanation for beet juice’s endurance-enhancing effects is that it reduces the oxygen cost of muscle contractions (which, for example, would improve running or cycling economy). In this case, there was no apparent difference in oxygen consumption, suggesting that there may be a different mechanism at work in repeated sprints. There are various theories about how nitrate supplementation might alter muscle contraction properties, but it’s not clear at this point exactly what’s happening.

Anyway, the cognitive results: there was no difference in the accuracy of the responses, but the non-beet-juice group had slower reaction times in the second half, while the beet juice group didn’t. Here’s what the results looked like:

When they looked more closely at the time dependence, the effects were biggest in the final third of each half, when fatigue would have been greatest. Again, the exact mechanism isn’t clear, but it may have to do with the amount of oxygen reaching the brain. When you’re exercising hard and hyperventilating, levels of carbon dioxide in your blood drop, which can in turn cause your blood vessels to constrict, reducing the amount of oxygen reaching your brain. The nitrate in beet juice, which is converted to nitric oxide, plays a crucial role in dilating blood vessels, so it may counteract this effect.

Anyway, the bottom line is that beet juice (and, more generally, nitrate-rich foods like leafy greens) aren’t just endurance-boosters – they seem to have other effects that are quite interesting for performance, and perhaps also for general health.

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