The idea that sleep is a passive resting state understates what is happening biologically during the night. Sleep is an active, programmed biological process during which some of the most important repair, hormone synthesis, and memory consolidation work of the 24-hour cycle occurs. For physical performance and longevity, the most consequential of these processes is growth hormone secretion, which peaks in its largest daily pulse during the first episode of slow-wave sleep, typically within the first 90 minutes of the night.
The NREM Stage 3 Window
Non-rapid eye movement Stage 3 sleep, slow-wave or deep sleep, is characterised by high-amplitude, low-frequency brain waves called delta waves. It is during this stage that the hypothalamus releases growth hormone-releasing hormone, stimulating the pituitary to secrete a large GH pulse. The magnitude of this pulse is directly related to the depth and duration of the slow-wave sleep episode. Anything that fragments or reduces the first sleep cycle, including alcohol consumption in the evening, late-night eating, noise disturbance, or sleep apnoea, attenuates this pulse.
Testosterone and Sleep Architecture
Testosterone synthesis in men is also sleep-dependent, though with a different timing profile. Testosterone rises during sleep and peaks in the early morning just before waking. Studies restricting sleep to 5 hours per night in healthy young men reduced testosterone levels by 10 to 15 percent within one week. The combination of impaired GH and testosterone secretion from poor sleep creates a hormonal environment that is simultaneously less anabolic and more catabolic, which is why adults who sleep poorly consistently show worse body composition outcomes than those who sleep well, independent of diet and exercise.
Sources
- Van Cauter, E., et al. (2000). Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA, 284(7), 861-868.
- Leproult, R., & Van Cauter, E. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 305(21), 2173-2174.
- Prinz, P.N., et al. (1983). Plasma growth hormone during sleep in young and aged men. Journal of Gerontology, 38(5), 519-524.