Historical text by DatBTrue, written between 2008 and 2016 and reproduced verbatim. It records what was argued then; it is not dosing guidance and not medical advice. Read the disclaimer.
There are two types of sleep, rapid eye movement (REM) and non-rapid eye movement (NREM). Sleep proceeds in cycles composed of four types of stages of NREM and a stage of REM usually ordered as: 1 > 2 > 3 > 4 > 3 > 2 > REM
The cycle lasts on average 90 to 110 minutes, with a greater quantity of stages 3 and 4 experienced early in the night and more REM later in the night.
NREM accounts for 75–80% of total sleep time. Non-REM is comprised of four stages; stages 1 and 2 are considered ‘light sleep’, and 3 and 4 ‘deep sleep’ or slow-wave sleep (SWS).
It has been shown that sleep, more specifically slow-wave sleep (SWS), does affect growth hormone levels in adult men. During eight hours sleep, it has been demonstrated in several studies that the men with a high percentage of SWS (average 24%) also had high growth hormone secretion, while subjects with a low percentage of SWS (average 9%) had low growth hormone secretion.
In one very complete study referenced by several others, it was demonstrated that “GH secretory rates and peripheral GH concentrations were maximally correlated with sleep stage, with lags of 4.5 and 16 min, respectively, suggesting that maximal GH release occurs within minutes of the onset of stage 3 or 4 sleep”.
Furthermore “sleep-related augmentation of GH secretion… usually occurs around midnight and the GH levels at that time are, as a rule, at their highest during the 24-hour period. Partially, this phenomenon is time-entrained and partially related to sleep itself. It is associated with a slow wave sleep, and the maximal GH levels occur within minutes of the onset of slow wave sleep” -Holl RW, Hartman ML, Veldhuis JD, et al. Thirty-second sampling of plasma growth hormone in man: correlation with sleep stages. J Clin Endocrinol Metab 1991;72:854–61.
The origin of nocturnal GH release in humans is still unknown. Most likely hypothalamic GHRH release is a major contributing component, but an additional role of another factor, presumably augmenting GHRH responsiveness of the somatotrophs, is likely. However the precise explanatory mechanisms are still not fully identified.
It is worth reiterating though that nocturnal release of GH makes up only a fraction of the total daily GH release in women, but the bulk of GH output in men.