Melatonin and affective disorders

The pineal hormone melatonin has a clear 24 h rhythm with a nocturnal peak. Serum melatonin concentrations have been reported to be decreased in subgroups of patients with affective disorders. When clusters of clinical items were correlated with the maximal nocturnal melatonin levels, significant negative regressions were found for items interpreted as retardation symptoms, especially those related to emotional or conative functions. These results point to the possibility of a 'low melatonin syndrome' in depression, characterized by low nocturnal serum levels of melatonin, an abnormal dexamethasone suppression test, a disturbed 24 h rhythm in cortisol levels and a less pronounced daily and annual cyclic variation in depressive symptomatology. Healthy persons show a rebound increase of nocturnal serum melatonin levels following evening suppression by bright light. One hour of the same light exposure did not alter the nocturnal melatonin levels in patients with major depressive disorders. This indicates a possible alteration in the pineal response to environmental lighting in depressed patients. The studies reported support the hypothesis of a decreased pineal function in some types of affective disorders.