Regulatory, Integrative and Comparative Physiology

Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights

Derk-Jan Dijk, David F. Neri, James K. Wyatt, Joseph M. Ronda, Eymard Riel, Angela Ritz-De Cecco, Rod J. Hughes, Ann R. Elliott, G. Kim Prisk, John B. West, Charles A. Czeisler


Sleep, circadian rhythm, and neurobehavioral performance measures were obtained in five astronauts before, during, and after 16-day or 10-day space missions. In space, scheduled rest-activity cycles were 20–35 min shorter than 24 h. Light-dark cycles were highly variable on the flight deck, and daytime illuminances in other compartments of the spacecraft were very low (5.0–79.4 lx). In space, the amplitude of the body temperature rhythm was reduced and the circadian rhythm of urinary cortisol appeared misaligned relative to the imposed non-24-h sleep-wake schedule. Neurobehavioral performance decrements were observed. Sleep duration, assessed by questionnaires and actigraphy, was only ∼6.5 h/day. Subjective sleep quality diminished. Polysomnography revealed more wakefulness and less slow-wave sleep during the final third of sleep episodes. Administration of melatonin (0.3 mg) on alternate nights did not improve sleep. After return to earth, rapid eye movement (REM) sleep was markedly increased. Crewmembers on these flights experienced circadian rhythm disturbances, sleep loss, decrements in neurobehavioral performance, and postflight changes in REM sleep.

  • microgravity
  • entrainment
  • sleep homeostasis
  • rapid eye movement sleep
  • adaptation
  • melatonin
  • slow-wave sleep
  • cortisol
  • memory


  • This research was supported by NASA Grant NAS9-19435 and National Institute on Aging Grant NAG9-1035. NASA supported this work through NASA Cooperative Agreement NCC9-58 with National Space Biomedical Research Institute Grants HPF.00202 and HPF.001.04.

  • Address for reprint requests and other correspondence: D.-J. Dijk, Centre for Chronobiology, School of Biomedical and Life Sciences, Univ. of Surrey, Guildford GU2 7XH, UK (E-mail:d.j.dijk{at}

  • The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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