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Human Growth Hormone and sleep

The graphs below taken from a 1968 study demonstrate the relationship between sleep and secretion of somatotropin, otherwise known as Human Growth Hormone.

Chart 1 - Normal secretory pattern of Human Growth Hormone and insulin in relation to sleep cycles.

Chart 2 - Secretory pattern of Human Growth Hormone and insulin relating to delayed sleep. Notice that the normal peak secretion of hGH does not occur when sleep is delayed from the usual bedtime. Since hGH releases fat and prevents the storage of excess fat, irregular sleep habits are likely to have a major negative impact on a person's ability to maintain their ideal weight. Notice also that insulin takes a lot longer to return to low levels if a person stays awake later than usual at night.

Chart source:
Takahashi Y, Kipnis DM, Daughaday WH, Growth hormone secretion during sleep, Washington University School of Medicine, Department of Medicine, Metabolism Division, St. Louis, Missouri, Published in The Journal of Clinical Investigation, Sep 1968; 47(9): 2079–2090