Sleep, Circadian Rhythm, and Antiaging Medicine: Sleep Disorders and Antiaging

Human sleep is classified into two qualitatively different stages: non-REM sleep and REM sleep. Non-REM sleep is further divided into three stages, N1 to N3 (light to deep), based on the depth of sleep (brain wave activity). Deep non-REM sleep (stage N3) is determined when slow waves (large brain waves that oscillate slowly at 0.5–2.0 Hz with an amplitude of 75 μV) are present more than 20% of the time, hence stage N3 is also referred to as slow wave sleep (SWS). The non-REM-REM sleep cycle lasts approximately 60–120 min (average about 90 min), and as sleep progresses into the latter half, the duration of non-REM sleep shortens, and the appearance of sleep slow waves decreases. Sleep also changes with age. Due to changes in the body clock with age, older people tend to go to bed and wake up earlier than younger people. Also, sleep time decreases with age, especially slow wave sleep decreases, and the time of awakening in the middle of sleep increases [1] (Fig. 60.1). People who are sleep-deprived appear less attractive to others. In a study involving healthy subjects, photographs of their faces without makeup were taken in a state of sufficient sleep and in a state of sleep deprivation after limiting sleep time to 4 h for two consecutive nights. When these photos were presented to other people, the sleep-deprived photos were perceived as less attractive, less healthy, and more sleepy, and people did not want to interact with them, but there was no difference in trustworthiness. Thus, we are sensitive to changes in appearance related to sleep, and securing sleep time is necessary for good human relationships.