Nitrate from vegetables such as beetroot is thought to improve performance in endurance sports, and plenty of athletes drink it on that basis. Individual trials are small and point in several directions. Pooling them is the only way to see whether anything survives.
A little, in power rather than in oxygen use. Across 73 studies with 1,061 participants in total, nitrate supplementation improved by a mean difference of 4.6 watts against placebo. It did not shift maximal oxygen uptake or , which are the measures people usually expect to move.
Nitrate supplementation is thought to improve performance in endurance sports, and the authors set out to meta-analyze the studies evaluating that effect in adults. They searched the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, Web of Science and CINAHL, without language restrictions.
Inclusion was narrow by design. A study had to compare nitrate supplementation with placebo, enroll adults engaging in an endurance-based activity, and report either a performance measure or a surrogate physiologic outcome.
Seventy-three studies met those criteria, with just over a thousand participants between them. Risk of bias was assessed with the Cochrane Collaboration tool, the data pooled with a , and confidence in the estimates graded with the GRADE approach.
The result is narrow but real. Nitrate supplementation improved power output, while maximal oxygen uptake and blood lactate levels did not move, and the authors conclude that benefits performance-related outcomes for endurance sports.
wat. About 4.6 watts more power, and no change in oxygen uptake.
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A few watts decide finishing positions, and knowing which measure moves tells you what the supplement is doing.
How do we know?
Gao and colleagues searched five databases without language restrictions, included only placebo-controlled studies in adults doing endurance activity, assessed risk of bias with the Cochrane tool and pooled with a random-effects model.
What is still unknown
The authors rate confidence in the estimates with GRADE, and a pooled benefit this size is easy to lose in a single race.
Learn something?
Where to next
What is the human body unusually good at?endurance
At what age does an athlete peak, and what does it depend on?endurance
What is the thirty-kilometer walk the monks of Mount Hiei make?endurance