No Influence Of Habitual Caffeine Consumption On Its Ergogenic Effects: A Systematic Review And Meta-analysis.

Abstract

Caffeine can improve exercise capacity and performance, although there appears to be substantial inter-individual variation in the performance response following caffeine intake. There is contrasting evidence as to whether habitual caffeine consumption influences the acute response to caffeine supplementation. PURPOSE: To quantify the proportion of the literature on caffeine supplementation that reports habitual caffeine consumption and determine its influence on the acute exercise response to caffeine supplementation using a systematic review and meta-analytic approach. METHODS: MedLine, Embase, and SPORTDiscus were searched, and articles were screened for inclusion/exclusion criteria. Random-effects meta-analyses and meta-regression models were used to examine the influence of habitual caffeine consumption on the overall ergogenic effects of caffeine and on different types of exercise types (endurance, strength, power). Subanalyses - were performed by acute relative dose (< 3, 3-6, > 6 mg/kg body weight), by whether the acute caffeine dose was lower or higher than the average daily caffeine dose, and by caffeine withdrawal time before the intervention (< 24, 24-48, > 48 h). RESULTS: Fifty-two (18%) of 289 caffeine studies contained sufficient information on habitual caffeine consumption to be included in the meta-analysis. There was a positive overall effect of caffeine compared with placebo (SMD=0.23, 95%CI: 0.19-0.28; p<0.001), with relative habitual caffeine consumption having no effect (p=0.99). Sub-analyses showed a significant ergogenic effect when the caffeine dose was <3 mg/kgBM (SMD=0.19, 95%CI: 0.09-0.29; p=0.004) and 3-6 mg/kgBM (SMD=0.25, 95%CI: 0.20-0.30; p<0.001), but not >6 mg/kgBM (SMD=0.12, 95%CI: -0.04-0.27; p = 0.10); when the dose was both higher (SMD=0.23, 95%CI: 0.18-0.28; p<0.001) and lower (SMD=0.19, 95%CI: 0.01-0.38; p=0.04) than the habitual caffeine dose; and when withdrawal was <24h, 24-48h and >48h. Caffeine was effective for endurance, strength and endurance training, with no influence of relative habitual caffeine consumption within exercise types (all p>0.05). CONCLUSION: Habitual caffeine consumption does not appear to influence the acute ergogenic effects of caffeine.