title: Combined caffeine and carbohydrate ingestion: effects on nocturnal sleep and exercise performance in athletes.
abstract: OBJECTIVE
  In athletes, caffeine use is common although its effects on sleep have not been widely studied. This randomised, double-blind, placebo-controlled crossover trial investigated the effects of late-afternoon caffeine and carbohydrate-electrolyte (CEB) co-ingestion on cycling performance and nocturnal sleep.
  
  
  METHODS
  Six male cyclists/triathletes (age 27.5 ± 6.9 years) completed an afternoon training session (TS; cycling 80 min; 65% VO₂max) followed by a 5 kJ kg(-1) cycling time trial (TT). Caffeine (split dose 2 × 3 mg kg(-1)) or placebo was administered 1 h prior and 40 min into the TS. A 7.4% CEB (3 ml kg(-1) every 15 min) was administered during the TS, followed 30 min after by a standardised evening meal. Participants retired at their usual bedtime and indices of sleep duration and quality were monitored via polysomnography.
  
  
  METHODS
  mean ± SD.
  
  
  RESULTS
  All participants performed better in the caffeine TT (caffeine 19.7 ± 3.3; placebo 20.5 ± 3.5 min; p = 0.006), while ratings of perceived exertion (caffeine 12.0 ± 0.6; placebo 12.9 ± 0.7; p = 0.004) and heart rate (caffeine 175 ± 6; placebo 167 ± 11 bpm; p = 0.085) were lower in the caffeine TS. Caffeine intake induced significant disruptions to a number of sleep indices including increased sleep onset latency (caffeine 51.1 ± 34.7; placebo 10.2 ± 4.2 min; p = 0.028) and decreased sleep efficiency (caffeine 76.1 ± 19.6; placebo 91.5 ± 4.2%; p = 0.028), rapid eye movement sleep (caffeine 62.1 ± 19.6; placebo 85.8 ± 24.7 min; p = 0.028) and total sleep time (caffeine 391 ± 97; placebo 464 ± 49 min; p = 0.028).
  
  
  CONCLUSIONS
  This study supports a performance-enhancing effect of caffeine, although athletes (especially those using caffeine for late-afternoon/evening training and competition) should consider its deleterious effects on sleep.
authors.affiliation: Exercise, Health and Performance, Faculty of Health Sciences, The University of Sydney, P.O. Box 170, Lidcombe, NSW, 1825, Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Miller
authors.forename: Helen
authors.initials: H
authors.lastname: O'Connor
authors.forename: Rhonda
authors.initials: R
authors.lastname: Orr
authors.forename: Patricia
authors.initials: P
authors.lastname: Ruell
authors.forename: Hoi Lun
authors.initials: HL
authors.lastname: Cheng
authors.forename: Chin Moi
authors.initials: CM
authors.lastname: Chow
mesh_terms: D000328:Adult; D056352:Athletes; D054874:Athletic Performance; D001642:Bicycling; D002110:Caffeine / Q000008:administration & dosage*; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004311:Double-Blind Method; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D058573:Performance-Enhancing Substances / Q000008:administration & dosage*; D010807:Physical Endurance / Q000187:drug effects*; D017286:Polysomnography; D012890:Sleep / Q000187:drug effects*; D055815:Young Adult
chemical_list: D004040:Dietary Carbohydrates; D058573:Performance-Enhancing Substances; D002110:Caffeine