Growth Hormone Increase Induced by Oral Administration of Melatonin in a Young Woman With Sleep Disturbances

Growth hormone (GH) secretion by the pituitary is regulated by stimulatory and inhibitory pathways such as growth hormone releasing hormone (GHRH) and somatostatin, respectively, being also modulated by different neurotransmitters acting at the hypothalamic/pituitary level. The pineal gland hormone melatonin regulates GH secretion in many mammals, including humans, although its role in modulating GH secretion has been debated. We describe the case of a young woman chronically taking melatonin for sleep disturbances, referring to her general practitioner for flushing that appeared just after starting melatonin intake. Laboratory findings showed elevated plasma levels of GH and insulin-like growth factor-1 (IGF-1). She did not show clinical features resembling acromegaly. The evaluation of pituitary and pituitary end organ hormones showed normal plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), estradiol, free thyroid hormones, cortisol, and prolactin. Urinary 5-hydroxyindoleacetic acid levels were normal. One month after melatonin withdrawal, her plasma levels of GH, together with IGF-1, completely normalized. An oral glucose suppression test showed a normal response of GH secretion, further excluding an autonomous secretion. Physicians should be aware of the possible interference of melatonin on GH secretion to prevent misleading diagnosis of autonomous secretion thus avoiding valueless and costly clinical investigations.