Subjective and objective measures of adaptation and readaptation to night work on an oil rig in the North Sea

Sleep. 2006 Jun;29(6):821-9. doi: 10.1093/sleep/29.6.821.


Study objectives: To study the adaptation and readaptation processes to 1 week of night work (6:30 PM to 6:30 AM) followed by 1 week of day work (6:30 AM to 6:30 PM).

Design: Part of a randomized, placebo-controlled, crossover field study. Here, data from the placebo arm are presented.

Setting: Oil rig in the North Sea. Work schedule: 2 weeks on a 12-hour shift, with the first week on the night shift and the second week on the day shift.

Participants: Subjects complaining about problems with adjusting to shift work. Seventeen workers completed the study.

Interventions: N/A.

Measurements: Subjective and objective measures of sleepiness (Karolinska Sleepiness Scale and simple serial reaction time test) and sleep (diary and actigraphy).

Results: Both subjective and objective measures improved gradually during night work. The return to day work after 1 week on the night shift led to a clear increase in subjective sleepiness and worsening of sleep parameters. During the week on the day shift, sleepiness and sleep gradually improved, similar to the improvement seen during night work. The workers indicated that the day shift was worse than the night shift on some of the measures, e.g., sleep length was significantly longer during the night-shift period.

Conclusions: This is one of few studies showing how shift workers in a real-life setting adjust to night work. Both subjective and objective sleepiness and subjective sleep improved across days. The effects were especially pronounced for the subjective data.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological*
  • Adult
  • Antioxidants / therapeutic use*
  • Cross-Over Studies
  • Disorders of Excessive Somnolence / diagnosis
  • Disorders of Excessive Somnolence / epidemiology
  • Humans
  • Male
  • Melatonin / therapeutic use*
  • Middle Aged
  • North Sea
  • Petroleum*
  • Reaction Time / physiology
  • Severity of Illness Index
  • Sleep Disorders, Circadian Rhythm / diagnosis*
  • Sleep Disorders, Circadian Rhythm / drug therapy*
  • Sleep Disorders, Circadian Rhythm / physiopathology


  • Antioxidants
  • Petroleum
  • Melatonin