title: Caffeine improves reaction time, vigilance and logical reasoning during extended periods with restricted opportunities for sleep.
abstract: BACKGROUND
  Various occupational groups are required to maintain optimal physical and cognitive function during overnight periods of wakefulness, often with less than optimal sleep. Strategies are required to help mitigate the impairments in cognitive function to help sustain workplace safety and productivity.
  
  
  OBJECTIVE
  To test the effectiveness of repeated 200 mg doses of caffeine on cognitive function and live-fire marksmanship with soldiers during three successive nights of sustained wakefulness followed by 4-h afternoon sleep periods.
  
  
  METHODS
  Twenty Special Forces personnel (28.6 ± 4.7 years, 177.6 ± 7.5 cm and 81.2 ± 8.0 kg) were randomly assigned to receive four 200-mg doses of caffeine (n = 10) or placebo (n = 10) during the late evening and early morning hours during three successive days. An afternoon 4-h sleep period followed. The psychomotor (PVT) and field (FVT) vigilance, logical reasoning (LRT) tests and a vigilance monitor assessed cognitive function throughout the study. Live-fire marksmanship requiring friend-foe discrimination was assessed.
  
  
  RESULTS
  Caffeine maintained speed on the PVT (p < 0.02), improved detection of events during FVT (p < 0.001), increased number of correct responses to stimuli as assessed by the vigilance monitor (p < 0.001) and increased response speed during the LRT (p < 0.001) throughout the three overnight testing periods. Live-fire marksmanship was not altered by caffeine.
  
  
  CONCLUSIONS
  A total daily dose of 800 mg caffeine during successive overnight periods of wakefulness is an effective strategy to maintain cognitive function when optimal sleep periods during the day are not available.
authors.affiliation: Behavioral Biology Branch, Center for Psychiatry and Neuroscience, Walter Reed Army Institute of Research, BLD 503, Silver Spring, MD, 20910, USA.
authors.forename: Gary H
authors.initials: GH
authors.lastname: Kamimori
authors.forename: Tom M
authors.initials: TM
authors.lastname: McLellan
authors.forename: Charmaine M
authors.initials: CM
authors.lastname: Tate
authors.forename: David M
authors.initials: DM
authors.lastname: Voss
authors.forename: Phil
authors.initials: P
authors.lastname: Niro
authors.forename: Harris R
authors.initials: HR
authors.lastname: Lieberman
mesh_terms: D000328:Adult; D001143:Arousal / Q000187:drug effects*; D001288:Attention / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003071:Cognition / Q000187:drug effects*; D006801:Humans; D008297:Male; D008889:Military Personnel; D009043:Motor Activity / Q000187:drug effects; D011597:Psychomotor Performance / Q000187:drug effects*; D011930:Reaction Time / Q000187:drug effects*; D012890:Sleep / Q000502:physiology*; D014851:Wakefulness; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine