title: Depression and circadian typology.
abstract: BACKGROUND
  The relationship between circadian disruptions and depressive disorders is a topic of great interest in contemporary psychiatry. Circadian rhythms include all physiological processes displaying a period around 24 hours. Sleep/wake cycles, body temperature, hormone secretion and other functions are subjected to person's individual circadian rhythm. Circadian typology includes three chronotypes: morning, neither and evening. The aim of this study was to examine the chronobiological aspects of depression.
  
  
  METHODS
  This cross-sectional study aimed to determine circadian rhythmic expression in 60 patients suffering from depression. The patients were in remission and were treated as outpatients at the Department of Psychiatry of the University Hospital Center Zagreb. The data were compared to a control group consisting of 40 medical workers employed at the University Hospital Centre Zagreb. A self-report measure of circadian typology was utilized - the Morningness-Eveningness Questionnaire.
  
  
  RESULTS
  According to our findings, among depressed patients 35% were morning, 58.3% neither and 6.7% evening types. In the control group 46% were morning, 48% neither and 6.0% evening types. Depressed patients reported stronger morning fatigue. Further, they tended to go to sleep earlier and felt more tired earlier in the evening, and they were less prone to choosing morning periods for completing complex cognitive tasks.
  
  
  CONCLUSIONS
  This study supports the association between depression and some alterations in circadian rhythms of behavior and sleep. Depression may be considered as the consequence or trigger of circadian disturbances. However, both depression and circadian rhythm disturbances may have a common aetiology: a decreased cellular resilience associated with lower resistance to stressful events.
authors.affiliation: Department of Emergency Medicine, Sisters of Charity University Hospital Centre, Vinogradska c. 29, 10000 Zagreb, Croatia, jelena.bielen87@gmail.com.
authors.forename: Jelena
authors.initials: J
authors.lastname: Bielen
authors.forename: Anja
authors.initials: A
authors.lastname: Melada
authors.forename: Ivona
authors.initials: I
authors.lastname: Markelić
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D003863:Depression / Q000503:physiopathology*; D005221:Fatigue / Q000503:physiopathology*; D006801:Humans; D057566:Self Report; D012890:Sleep / Q000502:physiology*; D020178:Sleep Disorders, Circadian Rhythm / Q000503:physiopathology*