Saf Health Work.  2018 Jun;9(2):203-209. 10.1016/

Field Study of Effects of Night Shifts on Cognitive Performance, Salivary Melatonin, and Sleep

  • 1Department of Ergonomics, School of Health, Shiraz University of Medical Sciences, Shiraz, Iran.
  • 2Department of Ergonomics, School of Health, Hamadan University of Medical Sciences, Hamadan, Iran.
  • 3Department of Occupational Health, School of Health, Urmia University of Medical Sciences, Urmia, Iran.


Night shift work is associated with many problems such as sleep deprivation, sleepiness, decreased cognitive performance, increased human errors, and fatigue. This study set out to measure cognitive performance, melatonin rhythms, and sleep after different consecutive night shifts (7 vs. 4) among control room operators (CORs).
The participants included 60 CORs with a mean age of 30.2 years (standard deviation, 2.0) from a petrochemical complex located in Southern Iran. Cognitive performance was assessed using the n-back task and continuous performance test. To evaluate melatonin, saliva was collected and tested by enzyme-linked immunosorbent assay. To assess sleep and sleepiness, the Pittsburgh Sleep Quality Index and Karolinska Sleepiness Scale were used, respectively.
Individuals who worked 7 consecutive night shifts had a significantly better cognitive performance and sleep quality than those who worked 4 consecutive night shifts. However, salivary melatonin profile and sleepiness trend were not affected by shift type.
The main duty of CORs working night shifts at the studied industry included managing safety-critical processes through complex displays; a responsibility that demands good cognitive performance and alertness. It is suggested that an appropriate number of consecutive night shifts in a rotating shift system should be planned with the ultimate aim of improving CROs performance/alertness and enhancing safety.


melatonin; night shifts; performance; sleepiness
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