Reduced nocturnal melatonin secretion in chronic schizophrenia: relationship to body weight.

Melatonin was estimated by RIA in samples taken at 24.00 h and 08.00 h from twenty-one male chronic schizophrenics and twelve age--sex matched controls and subsequently in more frequent nocturnal samples from nine of the chronic schizophrenics. The 24.00 h melatonin level and the 24.00/08.00 h melatonin ratio were significantly reduced in the chronic schizophrenic patients. Similar results, with no evidence of subsidiary peaks of melatonin secretion, were obtained in those patients who were retested. No relationships between melatonin secretion and age or anterior pituitary hormone secretion were demonstrated, but an effect of body weight was noted which accounted, in part, for the difference between schizophrenics and controls. These results suggest that the low levels of melatonin noted in studies on depressed patients may not be specific and that body weight must be controlled in subsequent studies of melatonin secretion in patients with psychiatric disease.