Beetroot juice lifts VO2max — but mostly in amateurs

Beetroot juice is one of the few sports supplements with a plausible mechanism that most people can buy in a supermarket: it supplies inorganic nitrate, which can raise nitric oxide availability and in turn influence oxygen use during exercise. Previous reviews mostly bundled maximal oxygen uptake in with a grab bag of other performance outcomes, leaving the specific question of VO2max unresolved. VO2max is the headline measure of aerobic capacity, so knowing whether a drink shifts it, and in whom, has practical value. The training-status question matters too, because supplements often work best in people furthest from their ceiling.

The authors conducted a PRISMA 2020 systematic review and meta-analysis restricted to randomised and crossover placebo-controlled trials in healthy adults. Six databases were searched from inception to 31 January 2026, with eligibility requiring beetroot juice or beetroot-derived nitrate supplementation, an incremental or graded aerobic exercise test, a placebo comparator, and reported VO2max or VO2peak. Thirty-eight studies with 703 participants entered the quantitative synthesis. Pooled effects were calculated as Hedges' g under a random-effects model, with subgroup analysis by training status and dose, plus funnel-plot inspection and trim-and-fill adjustment for publication bias.

Beetroot juice produced a small but statistically significant improvement in VO2max/VO2peak versus placebo, with a standardised mean difference of 0.24 (95% CI 0.11 to 0.37) and moderate heterogeneity (I2 = 48.3%). Recreationally active participants showed a larger effect at SMD 0.38, whereas in highly trained athletes the effect was 0.07 with a confidence interval spanning zero, so no clear benefit was demonstrated. Standard nitrate doses of 6.4 to 12.8 mmol and supplementation lasting at least three consecutive days gave the most consistent effects. Funnel plot asymmetry suggested possible small-study effects, and after trim-and-fill the pooled estimate fell to 0.19 (95% CI 0.07 to 0.31) while remaining significant.

This sharpens rather than overturns the existing nitrate literature, confirming a genuine but modest effect on maximal oxygen uptake and pinning the benefit to less-trained people. It complicates the marketing narrative aimed at competitive athletes, where the pooled effect was indistinguishable from placebo and the evidence base remains thin. The publication-bias signal is a reminder that small crossover trials with positive results are easier to publish, and the adjusted estimate is the more conservative number to carry forward. Open questions include whether chronic loading beyond a few days adds anything, and why highly trained individuals appear less responsive.

This is a reason to think beetroot juice has a real, if small, effect on aerobic capacity in people who train recreationally rather than competitively. The pattern in the data favoured multi-day supplementation over a single serving, and the effect in elite performers was not clearly shown. Because the effect size is small and shrank once publication bias was accounted for, it is better framed as a marginal addition than a substitute for training. Anyone tracking their own aerobic capacity should expect changes from training to dwarf anything from a drink.