Background: Beetroot juice (BRJ) is a dietary source of inorganic nitrate that may increase nitric oxide bioavailability and influence aerobic exercise capacity. Previous reviews have included scattered evidence on maximal or peak oxygen uptake in the context of overall exercise performance. This review assessed the effect of BRJ supplementation on VO2max/VO2peak in healthy adults. Methods: This systematic review and meta-analysis of randomized and crossover placebo-controlled trials was conducted in accordance with PRISMA 2020. A total of six databases were searched from inception to 31 January 2026. To be eligible for inclusion, studies had to involve terms such as healthy adults, BRJ or beetroot-derived nitrate supplementation, an incremental or graded aerobic exercise test, a placebo comparator, and reporting of VO2max or VO2peak. Pooled effects were calculated as Hedges` g under a random-effects model. Results: Thirty-eight studies involving 703 participants were included in the quantitative synthesis. BRJ produced a small statistically significant improvement in VO2max/VO2peak compared with placebo (SMD=0.24, 95% CI [0.11, 0.37], p<0.001; I2=48.3%). Effects were larger in recreationally active participants (SMD=0.38) and were not clearly demonstrated in highly trained athletes (SMD=0.07, 95% CI [-0.09, 0.23]). Standard nitrate doses of 6.4-12.8mmol NO3- and supplementation lasting at least 3 consecutive days showed the most consistent effects. Funnel plot asymmetry suggested possible small-study effects; after trim-and-fill adjustment, the pooled estimate was attenuated but remained statistically significant (SMD=0.19, 95% CI [0.07, 0.31]). Conclusion: BRJ supplementation is associated with a small improvement in VO2max/VO2peak, particularly in recreationally active adults. The effect may be smaller after adjusting for publication bias, and evidence in highly trained athletes remains limited and uncertain. The overall certainty of evidence was rated as moderate.
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