Evening naps and caffeine as countermeasures for sleepiness during night shift: a field study

Details

• Personal Author:
  Erman MK ; Mitler MM ; Schweitzer PK ; Stone KL ; Walsh JK ; West AJ
• Description:
  Introduction: Caffeine and/or napping prior to the night shift improves alertness and sustained attention in a 4-night simulated shift protocol, with the combination of napping and caffeine being slightly better than either napping or caffeine alone. The effectiveness of these combined countermeasures was tested in a field study during actual night shift work. Methods: Subjects (Ss) at 2 study sites participated in a 4-consecutive night crossover study comparing 2 conditions: (1) evening nap prior to the night shift on the first 2 nights plus caffeine 300 mg on all 4 nights (NC), and (2) placebo without napping all 4 nights (P). Condition order was counterbalanced. Thirty-nine Ss complied with the protocol and completed both study arms (28 m, 11 f; mean age 33, range 20-54). Caffeine or placebo was taken at the start of each shift. Three times during each night (at start, midway, and end of shift) Ss completed a 15- minute psychomotor vigilance task (PVT), the Karolinska Sleepiness Scale (KSS), and the Profile of Mood States (POMS). Ss slept at home during their usual hours, kept a sleep diary, and were monitored actigraphically. ANOVAs with repeated measures for condition, night, and time of night were the primary statistical method. A reciprocal transformation was used for reaction time of the slowest 10% of PVT responses (RT10) and a square root transformation was applied to PVT lapses (i.e., reaction time > 500 msec). Because of technical problems complete actigraphy data are available for only 25 Ss. Results: Actigraph-estimated total sleep times (ATST) during the 2 NC evening naps were 73 and 58 minutes. ATST for daytime sleep did not differ between conditions; mean ATST for days 1-3 were 276, 312, and 316 minutes for NC, and 298, 333, and 304 minutes for P. In contrast, Ss reported sleeping less following nights 1 and 2 in the NC condition compared to P (p < .01). RT10 worsened across nights 1-4 (F(3,93)=17.5, p<.001) and showed a condition by time interaction (F(1,31)=8.7, p=.006). For P only, RT10 worsened from shift start (2.54) to shift end (2.24). In addition, at shift end, P RT10 was worse (2.24) than NC RT10 (2.43; p=.04). PVT lapses also showed a condition by time interaction (F(1,31)=5.0, p=.03). Transformed lapse frequency increased from 3.56 at shift start to 4.44 at shift end for P with no change for NC during the night. Lapses were more frequent across nights 1-4 (F(3,93)=15.5, p<.001). Mean transformed numbers of lapses were 2.88, 3.73, 4.37, and 4.23 for NC nights 1-4, and 3.38, 3.94, 4.3, and 4.38 for P nights 1-4. Subjective sleepiness showed a condition by time interaction (F(1,31)=13.0, p=.001) with increased sleepiness at shift end during P compared to NC (KSS=6.3 vs 5.6, p=.006). There was no change in sleepiness ratings across nights 1-4. Conclusion: This rare field study of night shift workers documented that: 1) performance and alertness declined late in the night shift, 2) alertness and performance did not improve across successive night shifts (as found in some laboratory simulations), 3) a combination of napping and caffeine had modest positive effects on performance and subjective sleepiness in the early morning hours, and 4) daytime sleep duration of night workers is frequently less than 5 hours. [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 Monitoring-systems Physiological-effects Psychomotor-function Shift-work Shift-workers Sleep-deprivation Sleep-disorders Statistical-analysis Workers

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• ISSN:
  0161-8105
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Abstract or Summary
• Place as Subject:
  Missouri ; OSHA Region 7
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Volume:
  27
• NIOSHTIC Number:
  nn:20045718
• Citation:
  Sleep 2004 Jun; 27(Abstract Suppl):A69
• Federal Fiscal Year:
  2004
• Performing Organization:
  UACS, Inc.
• Peer Reviewed:
  False
• Start Date:
  19990930
• Source Full Name:
  Sleep
• Supplement:
  Abstract Supplement
• End Date:
  20020929
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:8e17ba6d0db17bc9c165d849e765e280c3aac3d419bce65516696cb89af79398b36a08ee25fea145f42e15c40a0374fe8f25d110c9a07b4d91eb5a06032c602d
• Download URL:
  https://stacks.cdc.gov/view/cdc/201028/cdc_201028_DS1.pdf
• File Type:
  [PDF - 231.26 KB ]