The significance of sleep onset and slow wave sleep for nocturnal release of growth hormone (GH) and cortisol.
Level 2 - randomized trial
Randomized crossover trial in human subjects
PubMed 3406323 · doi:10.1016/0306-4530(88)90021-2
What was done
Ten healthy male subjects underwent polysomnography and nocturnal blood sampling across three randomized experimental conditions: baseline sleep (2300 h to 0700 h), delayed sleep onset (kept awake until 0200 h, then sleep until 0700 h), and early-night slow-wave sleep (SWS) deprivation (acoustic tones delivered upon entering stage 3 sleep between 2300 h and 0200 h, followed by undisturbed sleep). Plasma growth hormone (GH) and cortisol profiles were measured.
What was found
The abstract reports no exact numerical hormone levels or confidence intervals. Directionally, baseline nights exhibited GH peaks concurrent with SWS alongside low cortisol levels. Delaying sleep onset to 0200 h substantially delayed both GH bursts and the timing of nocturnal cortisol release. Suppressing SWS between 2300 h and 0200 h did not significantly alter GH peak amplitude or reduce overall SWS duration (due to subsequent SWS rebound), but GH secretion occurred immediately following sleep onset rather than shifting to the post-0200 h SWS rebound period. SWS suppression had no significant effect on cortisol release.
Why it matters
These findings indicate that sleep onset is the critical physiological trigger timing nocturnal growth hormone and cortisol release, rather than slow-wave sleep architecture itself.
Limits
The study evaluated a very small sample (n = 10) consisting entirely of males. The abstract does not provide numerical hormone concentrations, variance, or exact statistical metrics, and acute laboratory sleep disruption may not generalize to chronic sleep disorders.