How does aging change hormonal release?
Changes to sleep architecture with aging are thought to lead to hormonal changes. Normal aging is associated with loss of SWS and REM, with increased sleep fragmentation. Recall that GH and PRL rise primarily in relation to the SWS of NREM, whereas TSH, cortisol, and testosterone increases are primarily under circadian control. In younger men, there is a dose-response relationship between SWS and GH secretion. For example, in 16- to 25-year-old males, SWS is nearly 20% of the sleep period and tails off to 5% to 10% at age > 40 years. This is associated with GH secretion during sleep of ∼350 mcg in the 16- to 25-year-old, but not > 100 mcg in individuals age > 35 years. Most of the PRL released during a 24-hour period is during sleep regardless of gender; there is nearly a 50% decrement in nocturnal PRL secretion with aging. The extent of circadian changes in cortisol and TSH are less dramatic with aging. Day–night TSH fluctuations also dampen with age.