title: Caffeine and diuresis during rest and exercise: A meta-analysis.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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 300 mg. 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 ± 195 mL or 16.0 ± 19.2% for caffeine ingestion vs. non-caffeine conditions. Subgroup meta-analysis 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.
authors.affiliation: Chinese Badminton Association, Zhejiang Jiaxing Branch, People's Republic of China. Electronic address: dr.zhang.yang@qq.com.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: National Personal Protective Technology Laboratory, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, United States.
authors.forename: Aitor
authors.initials: A
authors.lastname: Coca
authors.affiliation: Korey Stringer Institute, Department of Kinesiology, University of Connecticut, United States.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Casa
authors.affiliation: Farquhar College of Arts and Sciences, Exercise and Sports Science, Nova Southeastern University, United States.
authors.forename: Jose
authors.initials: J
authors.lastname: Antonio
authors.affiliation: Department of Health, Physical Education and Recreation, University of North Alabama, United States.
authors.forename: James M
authors.initials: JM
authors.lastname: Green
authors.affiliation: Department of Kinesiology, University of Alabama, United States.
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Bishop
mesh_terms: D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004231:Diuresis / Q000187:drug effects*; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012146:Rest; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine
keywords: Coffee; Dehydration; Diuretic; Fluid balance; Methylxanthine