Table 3.

Summary of consistent findings on the alterations of two major neurohumoral systems regulating circadian rythm in psychiatric disorders

Diagnosis	Neurohumoral system
	HPA axis	Melatonergic system
MDD	Elevated baseline cortisol levels, disruption on the dexamethasone suppression test results [159,160,258-261] increased cortisol/DHEA ratio162-164	Lower nocturnal melatonin levels, delayed melatonin secretion onset and offset [149,262-278]
BD	Increased cortisol and ACTH levels in manic phase	Higher melatonin levels in manic phase at the daytime [186]
	Findings about HPA axis abnormalities are seen both depressive and euthymic phase, it is preferred to evaluate them as state and trait marker due to clinical variations [199]	Findings about nocturnal melatonin levels among BD phases are inconsistent [119,188,189,279]
SCH	Baseline cortisol levels are inconsistent	Lower nocturnal melatonin levels, [280,281] phase advance in melatonin rhythm,223 the absence of melatonin rhythmicity [282]
	Blunted cortisol stress response [237]

MDD: major depressive disorder, BD: bipolar disorder, SCH: schizophrenia, HPA: hypothalamic-pituitary-adrenal, DHEA: dehydroepiandrosterone, ACTH: adrenocorticotropic hormone