Effects of Caffeine Supplementation on Physical Performance of Soccer Players: Systematic Review and Meta-Analysis

Context: Caffeine is 1 of the most popular supplements consumed by athletes, and the evidence for improving soccer performance remains limited. Objective: To investigate and update the effects (benefits and harms) of caffeine to improve performance on soccer players. Data Sources: Electronic search in Medline (via PubMed), CENTRAL, Embase, SPORTDiscus, and LILACS, from inception to March 28, 2020. Study Selection: Randomized clinical trials (RCTs) assessing the effects of caffeine on the performance of soccer players. Study Design: Systematic review with meta-analysis. Data Extraction: Data extraction was conducted independently by 2 authors using a piloted form. We assessed methodological quality (Cochrane risk-of-bias [RoB] table) and the certainty of the evidence (GRADE [Grading of Recommendations Assessment, Development and Evaluation] approach). Results: Sixteen RCTs were included. Overall methodological quality was classified as unclear to low risk of bias. When assessing aerobic endurance, meta-analyses did not demonstrate the differences between caffeine and placebo (mean difference [MD], 44.9 m; 95% confidence interval [CI], -77.7 to 167.6). Similarly, no difference was observed during time to fatigue test (MD, 169.8 seconds; 95% CI, -71.8 to 411.6). Considering anaerobic power, meta-analyses also did not find differences for vertical jump (MD, 1.01 cm; 95% CI, -0.68 to 2.69) and repeated sprint tests (MD, -0.02 seconds; 95% CI, -0.09 to 0.04), as well as reaction time agility test (MD, 0.02 seconds; 95% CI, -0.01 to 0.04) and rating of perceived exertion (MD, 0.16 points; 95% CI, -0.55 to 0.87). Regarding safety, a few minor adverse events were reported. Based on the GRADE approach, the certainty of this evidence was classified as very low to low. Conclusions: We found no significant improvement in soccer-related performance with caffeine compared with placebo or no intervention. However, caffeine appears to be safe.

Automated summary

The study found that caffeine did not significantly improve the performance of soccer players, but it appears to be safe. Although some minor adverse events were reported, only a few studies support the positive effects of caffeine on soccer performance.