The rhythm of melatonin synthesized in and released from the pineal gland is characterized by a prominent nocturnal peak, which also contains temporal information that had originated in the suprachiasmatic nucleus. Strong reductions of circulating melatonin are also observed in numerous disorders and diseases, including Alzheimer's disease, various other neurological and stressful conditions, pain, cardiovascular diseases, cases of cancer, endocrine and metabolic disorders, in particular diabetes type 2.