Forskning

August 30, 2014

Caffeine and diuresis during rest and exercise: a meta‐analysis

Y Zhang et al, 2014, Caffeine and diuresis during rest and exercise: a meta‐analysis, Journal of Science and Medicine in Sport, published online ahead of print.

Meta‐Analysis – Diuresis/Fluid Balance

ABSTRACT: Objectives: Although ergogenic, acute caffeine ingestion may increase urine volume, prompting concerns about fluid balance during exercise and sport events. This meta‐analysis evaluated caffeine induced diuresis in adults during rest and exercise. Design: Meta‐analysis. Methods: A search of three databases was completed on November 1, 2013. Only studies that involved healthy adults and provided sufficient information concerning the effect size (ES) of caffeine ingestion on urine volume were included. Sixteen studies met the inclusion criteria, providing a total of 28 ESs for the meta‐analysis. Heterogeneity was assessed using a random‐effects model. Results: The median caffeine dosage was 300mg. The overall ES of 0.29 (95% confidence interval (CI)=0.11‐0.48, p=0.001) corresponds to an increase in urine volume of 109±195mL or 16.0±19.2% for caffeine ingestion vs. non‐caffeine conditions. Subgroup metaanalysis confirmed exercise as a strong moderator: active ES=0.10, 95% CI=‐0.07 to 0.27, p=0.248 vs. resting ES=0.54, 95% CI=0.22‐0.85, p=0.001 (Cochran’s Q, p=0.019). Females (ES=0.75, 95% CI=0.38‐ 1.13, p<0.001) were more susceptible to diuretic effects than males (ES=0.13, 95% CI=‐0.05 to 0.31, p=0.158) (Cochran’s Q, p=0.003). Conclusions: Caffeine exerted a minor diuretic effect which was negated by exercise. Concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise.