title: Cortisol and α-Amylase Secretion Patterns between and within Depressed and Non-Depressed Individuals.
abstract: OBJECTIVE
  Associations between biological stress markers and depression are inconsistent across studies. We assessed whether inter- and intra-individual variability explain these inconsistencies.
  
  
  METHODS
  Pair-matched depressed and non-depressed participants (N = 30) collected saliva thrice a day for 30 days, resulting in 90 measurements per individual. The relationships between measures of stress-system function and depression were examined at the group level by means of mixed model analyses, and at the individual level by means of pair-matched comparisons. The analyses were repeated after adjusting for time-varying lifestyle factors by means of time-series regression analyses.
  
  
  RESULTS
  Cortisol and α-amylase levels were higher, the α-amylase/cortisol ratio larger, and the daily cortisol slope steeper in the depressed compared to the non-depressed group. Adjusting for lifestyle factors and antidepressant use reduced the associations under study. In 40%-60% of the matched comparisons, depressed individuals had higher cortisol and α-amylase levels, a larger α-amylase/cortisol ratio, and a steeper daily slope than their non-depressed match, regardless of adjustment.
  
  
  CONCLUSIONS
  Our group-level findings were mostly in line with the literature but generalization to individuals appeared troublesome. Findings of studies on this topic should be interpreted with care, because in clinical practice the focus is on individuals instead of groups.
authors.affiliation: Interdisciplinary Center Psychopathology and Emotion regulation, Department of Psychiatry, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Sanne H
authors.initials: SH
authors.lastname: Booij
authors.affiliation: Interdisciplinary Center Psychopathology and Emotion regulation, Department of Psychiatry, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands; Center for Integrative Psychiatry, Lentis, Groningen, The Netherlands.
authors.forename: Elisabeth H
authors.initials: EH
authors.lastname: Bos
authors.affiliation: Interdisciplinary Center Psychopathology and Emotion regulation, Department of Psychiatry, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Mara E J
authors.initials: ME
authors.lastname: Bouwmans
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: van Faassen
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Ido P
authors.initials: IP
authors.lastname: Kema
authors.affiliation: Interdisciplinary Center Psychopathology and Emotion regulation, Department of Psychiatry, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Albertine J
authors.initials: AJ
authors.lastname: Oldehinkel
authors.affiliation: Interdisciplinary Center Psychopathology and Emotion regulation, Department of Psychiatry, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: de Jonge
mesh_terms: D056044:Actigraphy; D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000339:Affect; D000928:Antidepressive Agents / Q000627:therapeutic use; D002940:Circadian Rhythm / Q000502:physiology; D003863:Depression / Q000188:drug therapy / Q000503:physiopathology*; D003866:Depressive Disorder / Q000188:drug therapy / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007030:Hypothalamo-Hypophyseal System / Q000503:physiopathology*; D008019:Life Style; D008297:Male; D016555:Matched-Pair Analysis; D008499:Medical Records; D008875:Middle Aged; D009426:Netherlands; D010913:Pituitary-Adrenal System / Q000503:physiopathology*; D012463:Saliva / Q000737:chemistry*; D012636:Secretory Rate; D013312:Stress, Physiological / Q000502:physiology*; D055815:Young Adult; D000516:alpha-Amylases / Q000378:metabolism*
chemical_list: D000928:Antidepressive Agents; D000516:alpha-Amylases; D006854:Hydrocortisone