Sleepiness and driving events in shift workers: the impact of circadian and homeostatic factors

Sleep. 2019 Jun 11;42(6):zsz074. doi: 10.1093/sleep/zsz074.


We aimed to characterize objective and subjective sleepiness and driving events during short work commutes and examine the impact of circadian and homeostatic factors across different shift types in a shift worker population. Thirty-three nurses were monitored for 2 weeks over day (07:00-15:30), evening (13:00-21:30), and night shifts (21:00-07:30). Sleep was measured via daily sleep logs and wrist actigraphy. Driving logs were completed for each work commute, reporting driving events and a predrive Karolinska Sleepiness Scale (KSS). Ocular data from a subset of participants (n = 11) assessed objective sleepiness using infrared oculography during commutes. Circadian phase was assessed at three time points via urinary 6-sulphatoxymelatonin (aMT6s) collected over 24-48 hours. Subjective and objective sleepiness and sleep-related and hazardous driving events significantly increased following night shift compared with preshift. There were significant shift differences with KSS, sleep-related and inattention-related events highest during the postnight shift commute, compared with day and evening shifts. Sleep-related events were highest following the first night shift, while inattention-related events were most frequent after consecutive night shifts. KSS, sleep-related and hazardous events were increased during drives following ≥16 hours of wakefulness. KSS and sleep-related events increased during drives within ±3 hours of aMT6s acrophase. An interaction between homeostatic and circadian processes was observed, with KSS and sleep-related events highest within ±3 hours of acrophase, when wakefulness was ≥16 hours. In naturalistic conditions, subjective and objective sleepiness and driving events are increased following night shifts, even during short (~30 minutes) commutes and exacerbated by an interaction between circadian phase and duration of wakefulness.

Keywords: alertness; circadian; driving; homeostatic; shift work; sleep; wakefulness.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actigraphy
  • Adult
  • Automobile Driving*
  • Circadian Rhythm / physiology
  • Cognition
  • Female
  • Homeostasis
  • Humans
  • Male
  • Melatonin / analogs & derivatives
  • Melatonin / urine
  • Middle Aged
  • Nurses / statistics & numerical data
  • Shift Work Schedule / statistics & numerical data*
  • Sleep
  • Sleep Disorders, Circadian Rhythm / epidemiology*
  • Sleepiness*
  • Transportation
  • Wakefulness / physiology
  • Work Schedule Tolerance / physiology*
  • Young Adult


  • 6-sulfatoxymelatonin
  • Melatonin