The New England Journal of Medicine says,
The cardinal biologic manifestations of a major affective (depression) disorder consist of: alterations in the hypothalamic centers (of the brain) that govern food intake, libido, circadian rhythms, and the synthesis and release of hypothalamic hormones into hypophysial portal blood and the systemic circulation. Patients with melancholia (endogenous depression or major depression typically have anorexia, decreased sexual interest, altered timing of the cycle of rest and activity (i.e., early-morning awakening), diurnal variation in mood, and endocrine abnormalities such as hypercortisolism. In a typical depression, the defining characteristics include hyperphagia and hypersomnia.The first neuroendocrine investigations into major affective disorder rested on the demonstration that monoaminergic Clinical and Biochemical Manifestations of Depression, New England Journal of Depression) Philip W. Gold, M.D., Frederick K. Goodwin, M.D., and George P. Chrousos, M.D.N Engl J Med 1988; 319:413-420.
Experts tell us that the fundamental biological manifestation of endogenous depression also called major depression) consist of changes in the hypothamlic centers of the brain that govern food intake, sexual drive and circadian rhythms.. Circadian rhythms which involve the timing of the cycle of rest and activity are altered which results in symptoms being worse in the morning, (early morning awakening) and endocrine abnormalities such as increased stress hormones (cortisol)