The Effects of Combined Caffeine and Sodium Bicarbonate Supplementation on Exercise Performance, Physiological Responses, and Gastrointestinal Tolerability: A Systematic Review and Meta-Analysis

Background: Caffeine and sodium bicarbonate can individually enhance exercise performance, but whether their combined use provides additional benefits and how it affects physiological responses and gastrointestinal (GI) tolerability remain unclear. Objective: This systematic review and meta-analysis aimed to evaluate the effects of combined caffeine and sodium bicarbonate (CAF + SB) supplementation on exercise performance, physiological responses, and GI tolerability, and to determine whether it provides additional benefits compared with placebo or either supplement alone. Methods: PubMed, Web of Science, and SPORTDiscus were systematically searched from inception to 18 July 2026. Continuous outcomes were pooled using random-effects models and expressed as mean differences (MDs) or ratios of means (RoMs) with 95% confidence intervals (CIs), as appropriate. Within-participant correlations in crossover trials were accounted for, and robustness was examined using leave-one-out analyses and alternative correlation coefficients. Rating of perceived exertion (RPE) and GI symptoms were synthesized narratively. Results: Thirteen crossover trials were included. Compared with placebo, CAF + SB supplementation increased mean power (MD = 8.43 W, 95% CI = 1.85 to 15.00, p = 0.012) and reduced time-trial completion time (RoM = 0.984, 95% CI = 0.970 to 0.998, p = 0.022), corresponding to an estimated reduction of 1.6%. However, both findings were sensitive to the exclusion of individual studies in leave-one-out analyses, indicating limited robustness. CAF + SB did not significantly improve mean power compared with caffeine or sodium bicarbonate alone. Compared with placebo, CAF + SB increased blood HCO3− and post-exercise lactate concentrations, although the HCO3− evidence was limited by heterogeneity or few studies. Narrative findings showed no consistent effect on RPE or GI tolerability. Conclusions: CAF + SB supplementation may produce modest improvements in selected exercise-performance outcomes compared with placebo, but these findings are not robust because their statistical significance depends on individual studies. Current evidence does not establish an additional performance benefit over caffeine or sodium bicarbonate alone. The observed physiological responses do not, by themselves, demonstrate superior performance, and the gastrointestinal tolerability of CAF + SB remains uncertain.