Individual and Combined Effects of Acute Caffeine and Sodium Bicarbonate Supplementation on Exercise Performance and Metabolic Responses: A Bayesian Network Meta-Analysis of Co-Supplementation Trials.

Background: Caffeine and sodium bicarbonate (SB) are widely used ergogenic supplements that influence exercise performance through distinct physiological mechanisms and may differentially modulate exercise-related metabolic responses. Whether their co-ingestion provides benefits beyond either supplement alone remains uncertain. This study evaluated the incremental effects of caffeine and SB co-ingestion within trials specifically designed to investigate the combined supplementation strategy. Methods: A systematic review and Bayesian arm-based multilevel network meta-analysis of randomized controlled trials published up to May 2026 was conducted. Eligible studies investigated acute caffeine-SB co-supplementation and, where available, included caffeine-only and SB-only arms, with placebo as the common reference. Exercise performance was the primary outcome; blood lactate, blood pH, blood bicarbonate, and rating of perceived exertion were secondary outcomes. Effects were estimated using Hedges' g, Bayesian credible intervals, and SUCRA rankings. Results: Thirteen studies involving 181 participants met the eligibility criteria. Within this co-supplementation trial network, caffeine (g = 0.21), SB (g = 0.21), and co-ingestion (g = 0.28) produced small but credible improvements in exercise performance relative to placebo. However, comparisons among active conditions provided no clear evidence that co-ingestion was superior to either supplement alone. SB increased blood pH (g = 0.95) and blood lactate (g = 1.13), whereas caffeine reduced blood bicarbonate (g = -0.89). Co-ingestion elicited the largest increase in blood lactate (g = 1.75), but this response was not accompanied by a proportionally greater improvement in performance. Exploratory analyses suggested possible variation in supplementation responses according to training status. Conclusions: Within trials designed to evaluate caffeine-SB co-supplementation, the caffeine-only, SB-only, and combined conditions showed small improvements in exercise performance relative to placebo. However, co-ingestion elicited more pronounced metabolic responses without a clear performance advantage over either component alone, and the mechanisms underlying this divergence remain uncertain.