Alignment of circadian rhythms to daytime sleep improves performance and alertness in night shift workers

Details

• Personal Author:
  Crowley SJ ; Eastman CI ; Fogg LF ; Lee C ; Tseng, Chih-Yu
• Description:
  Introduction: Impaired performance, reduced alertness, and fatigue are common complaints of night shift workers. These problems occur because their circadian clock is not aligned to a night work and daytime sleep schedule. In this study, bright light during the night shift, melatonin before daytime sleep, a regular dark/sleep opportunity, and sunglasses during the commute home were tested to determine their ability to delay the circadian clock. The phase delays produced by various combinations of these interventions are reported in an accompanying abstract (Crowley et al). Here, we report performance and alertness during the night shifts and daytime sleep duration. Methods: During each of 5 consecutive simulated night shifts (23:00 to 07:00), subjects completed the Neurobehavioral Assessment Battery. Following each night shift, subjects had to stay in bed, in the dark, for a full seven hours (08:30 to 15:30). Subjects recorded bedtimes, sleep onset, and wake times on daily sleep logs (verified by wrist actigraphy). After the 5 night shifts, final circadian phase was assessed using salivary dim light melatonin onset (DLMO). The temperature minimum (Tmin) was estimated by adding 7 hours to the DLMO. Results: Subjects were divided into 3 groups: those whose final DLMO was <1:30 (n=10), i.e. the Tmin did not occur during the time of the previous daytime dark/sleep period ("non-shifters"); those whose final DLMO was >1:30 and <5:00 (n=16), i.e. the Tmin occurred in the first half of dark/sleep (partial re-entrainment); and those whose final DMLO was >5:00 (n=41), i.e. the Tmin occurred in the second half of dark/sleep (complete re-entrainment). There was no difference among the 3 groups in daytime sleep duration (mean +/- SD): 6.5 +/- 0.6, 6.6 +/- 0.3, and 6.7 +/- 0.2h. There was no difference in performance or alertness between the group who showed partial and the group who showed complete reentrainment. However, these two groups had significantly better performance and alertness than the non-shifters. For example, the average response time on the Psychomotor Vigilance Task during the last 3 night shifts for the non-shifters was twice as long (794 +/- 857 versus 301 +/- 40 and 311 +/- 79ms) with twice as many lapses (7.1 +/- 3.7 versus 3.5 +/- 1.6 and 3.7 +/- 2.2). They were also much sleepier (Stanford Sleepiness Scale: 5.1 +/- 1.3 versus 3.7 +/- 1.1 and 3.6 +/- 1.3). Conclusions: Even though all 3 groups slept almost all of the allotted 7 hours, there were differences during the night shift depending on the amount of phase delay. This shows that a reasonable amount of daytime sleep is not enough to reduce sleepiness or improve performance in night shift workers; some circadian alignment is needed. Furthermore, in young adults, complete re-entrainment is not necessary; partial reentrainment is enough to increase performance and alertness during the night shift. [Description provided by NIOSH]
• Subjects:
  Circadian Rhythm Men Occupational Health Safety Shift Work Schedule Sleep Sleep Initiation And Maintenance Disorders Women
• Keywords:
  Biological-function Circadian-rhythms Humans Physiological-effects Psychomotor-function Shift-work Shift-workers Sleep-deprivation Sleep-disorders Statistical-analysis
• ISSN:
  0161-8105
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Abstract or Summary
• Place as Subject:
  Illinois ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Volume:
  26
• NIOSHTIC Number:
  nn:20045661
• Citation:
  Sleep 2003 Jun; 26(Abstract Suppl):A97
• Federal Fiscal Year:
  2003
• Performing Organization:
  Rush University Medical Center, Chicago, Illinois
• Peer Reviewed:
  False
• Start Date:
  19990930
• Source Full Name:
  Sleep
• Supplement:
  Abstract Supplement
• End Date:
  20090430
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:fe5457b8bca6bf4354018e9dea40feddec40b02d479d67b1b2786e01c10abfefb787b08eb76d062adbeec984ddc1ca5de28aad75d2ad903bb0752d6143ddf4c1
• Download URL:
  https://stacks.cdc.gov/view/cdc/201006/cdc_201006_DS1.pdf
• File Type:
  [PDF - 29.71 KB ]