title: Relationship between circadian rhythm amplitude and stability with sleep quality and sleepiness among shift nurses and health care workers.
abstract: BACKGROUND
  Sleep is affected by the circadian cycle and its features. Amplitude and stability of circadian rhythm are important parameters of the circadian cycle. This study aims to examine the relationship between amplitude and stability of circadian rhythm with sleep quality and sleepiness.
  
  
  METHODS
  In this cross-sectional research, 315 shift nurses and health care workers from educational hospitals of Kerman University of Medical Sciences (KUMS), Iran, were selected using a random sampling method. The Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS) and Circadian Type Inventory (CTI) were used to collect the required data.
  
  
  RESULTS
  In this study, 83.2% suffered from poor sleep and one-half had moderate and excessive sleepiness. The results showed that flexibility in circadian rhythm stability, job stress and sleepiness are among the factors affecting quality sleep in shift workers.
  
  
  CONCLUSIONS
  Those whose circadian rhythm amplitude was languid suffered more from sleepiness and those whose circadian stability was flexible had a better sleep. Variables including circadian rhythm stability (flexible/rigid) and amplitude (languid/vigorous) can act as predictive indices in order to employ people in a shift work system so that sleepiness and a drop in quality of sleep are prevented.
authors.affiliation: a School of Health , Kerman University of Medical Sciences , Kerman , Iran.
authors.forename: Akram
authors.initials: A
authors.lastname: Jafari Roodbandi
authors.affiliation: b Research Center for Health Sciences , Shiraz University of Medical Sciences , Shiraz , Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Choobineh
authors.affiliation: c School of Medical Sciences , Tarbiat Modares University , Tehran , Iran.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Daneshvar
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006282:Health Personnel; D006801:Humans; D008297:Male; D008875:Middle Aged; D009729:Nursing; D009784:Occupational Diseases / Q000453:epidemiology*; D012890:Sleep / Q000502:physiology*; D020178:Sleep Disorders, Circadian Rhythm / Q000453:epidemiology*; D055815:Young Adult
keywords: circadian rhythm; nurses; shift work; sleep quality; sleepiness