What is the concern with sleep wake cycles and circadian rhythmicity?
The 24-hour profile of nearly all pituitary hormones is related to the presence and quality of sleep. Stereotypical changes in nearly all hormonal and metabolic variables are observed surrounding sleep cycling and sleep–wake transitions. The absence of sleep, or the interruption of sleep, has potent influences on hormonal ebb and flow. This adds another layer of control to hormone release on top of the well-known feedback loops. Understanding these reproducible changes in view of sleep wake–cycling is fundamental to recognizing normal and early abnormal endocrine processes. For example, appreciation of normal hormone changes during the day and night provides insight into a patient’s laboratory values drawn at varied times through a 24-hour period.