Laboratory and field studies of naps and caffeine as practical countermeasures for sleep-wake problems associated with night work

Sleep. 2006 Jan;29(1):39-50. doi: 10.1093/sleep/29.1.39.


Study objectives: To evaluate the effects of napping, caffeine, and napping plus caffeine on performance and alertness in both laboratory and field settings.

Design: (1) Laboratory Study: parallel-groups design with random assignment to 1 of 4 experimental conditions. (2) Field Study: crossover design.

Setting: Sleep laboratory and field settings.

Participants: (1) Laboratory Study: 68 healthy individuals; (2) Field Study: 53 shiftworkers who worked nights or rotating shifts.

Interventions: (1) Laboratory Study: an evening nap opportunity before the first 2 of 4 consecutive simulated night shifts plus placebo taken all 4 nights, caffeine taken nightly, the combination of the nap and caffeine conditions, or placebo. (2) Field Study: an evening nap on the first 2 of 4 consecutive night shifts plus caffeine taken nightly versus placebo taken nightly without naps.

Measurements and results: (1) Laboratory Study: Napping, caffeine, and their combination all improved alertness and performance as measured by Maintenance of Wakefulness Test and Psychomotor Vigilance Task, but the combination of napping and caffeine was best in improving alertness. (2) Field Study: Napping plus caffeine improved performance as measured by Psychomotor Vigilance Test and decreased subjective sleepiness in individuals working the night shift.

Conclusions: Napping plus caffeine helps improve performance and alertness of night-shift workers.

Publication types

  • Randomized Controlled Trial
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Arousal / drug effects
  • Caffeine / therapeutic use*
  • Central Nervous System Stimulants / therapeutic use*
  • Circadian Rhythm
  • Cross-Over Studies
  • Disorders of Excessive Somnolence / drug therapy*
  • Disorders of Excessive Somnolence / etiology*
  • Female
  • Humans
  • Laboratories
  • Male
  • Middle Aged
  • Occupational Diseases / complications
  • Psychomotor Performance / drug effects
  • Reaction Time / drug effects
  • Sleep Disorders, Circadian Rhythm / complications*
  • Sleep*


  • Central Nervous System Stimulants
  • Caffeine