Infancy: The REM to non-REM cycle is shorter. Around 4 weeks of age, the newborn's sleepy periods get longer. By 6 months of age, infants spend longer and more regular periods in non-REM sleep. Most begin sleeping through the night and taking naps in the morning and afternoon.
Childhood: By age 6, children are awake all day and sleep for about 10 hours each night. From age 7 to puberty, children are the most efficient sleepers. Nocturnal melatonin (a hormone produced by the body, especially at night, which aids sleep) production is at its highest peak. If a child is sleepy during the day at this age, it is cause for concern.
Adolescence: They need about an hour more sleep than as young children but they usually sleep an hour or so less.
Adulthood: Between the ages of 20-30, the amount of deep sleep drops by about half and nighttime awakenings double. By age 40, stage 4 sleep (see How Sleep Works) has almost disappeared. Women's reproductive cycles can greatly influence sleep. During pregnancy, many women are sleepy all the time and may log an extra two hours a night. During the second phase of the menstrual cycle, between ovulation and the next menses, some women fall asleep and enter REM sleep more quickly than usual.
Middle Age: Stage 3 sleep (see How Sleep Works) begins to diminish. Nighttime awakenings become more frequent and last longer. During menopause, many women experience hot flashes that can interrupt sleep, which can sometimes lead to chronic insomnia.
Old Age: By the time a person turns 65, melatonin production has declined to a low level, which makes sleep more difficult. Deep sleep accounts for less than 5% of sleep time and, in some, it is totally absent. Falling asleep takes longer and the shallow quality of sleep results in dozens of wakenings during the night.