(HealthDayNews) -- While you sleep, your body doesn't.
The Journal of Pediatric Endocrinology and Metabolism reports that your endocrine glands are at work all night long -- but not all at the same time. It all depends on how deeply you sleep.
Growth hormone starts secreting during the first phases of sleep, and continues during the deepest sleep periods.
Prolactin -- best known for its role in breast milk production and possibly immune system function -- is only secreted during deep sleep.
Thyroid stimulating hormone and cortisol, the stress hormone, aren't secreted until the deepest sleep periods are over and you start to wake up.
