Which hormone level peaks during sleep?

• A. Cortisol
• B. Calcitonin
• C. Growth hormone
• D. Progesterone

Answer: (C)

Growth hormone rises most during sleep, especially in the deepest stage of non-REM sleep that occurs in the first part of the night. The hypothalamus releases growth hormone–releasing hormone to stimulate the pituitary to secrete GH in pulses, while somatostatin dampens release. Sleep itself promotes more frequent and larger GH pulses, causing a nocturnal peak. This hormone drives tissue growth and repair, protein synthesis, and bone remodeling. Cortisol, by contrast, follows a daytime rhythm and is lowest during sleep, then increases toward morning; calcitonin regulates calcium with no sleep-related peak; progesterone levels vary with the menstrual cycle and pregnancy, not with sleep.