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During the recommended seven to nine hours of sleep, we typically go through three to five sleep cycles per night, with the duration of REM sleep getting longer each subsequent time, Varga explains.
Children need many hours of sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. [65] Early in 2015, after a two-year study, [ 91 ] the National Sleep Foundation in the US announced newly revised recommendations as shown in the table below.
Schematic illustration of a normal sleep cycle. The standard figure given for the average length of the sleep cycle in an adult man is 90 minutes. N1 (NREM stage 1) is when the person is drowsy or awake to falling asleep. Brain waves and muscle activity start to decrease at this stage. N2 is when the person experiences a light sleep.
The National Sleep Foundation recommends that adults aim for 7–9 hours of sleep per night, while children and teenagers require even more. For healthy individuals with normal sleep, the appropriate sleep duration for school-aged children is between 9 and 11 hours.
Some people only need six and a half hours of sleep every night, Atwood adds, whereas others may need more than nine hours to feel rested and function the next day.
Within a few months of postnatal development, there is a marked reduction in percentage of hours spent in REM sleep. By the time the child becomes an adult, he spends about 6–7 hours in NREM sleep and only about an hour in REM sleep. [46] [47] This is true not only of humans, but of many animals dependent on their parents for food. [48]
Adults should sleep 7 or more hours per night The eight-hours-a-night rule for adults is a bit of a myth, says Harris. “It’s not actually that everyone needs eight hours.
During a night of sleep, humans usually experience about four or five periods of REM sleep; they are shorter (~15 min) at the beginning of the night and longer (~25 min) toward the end. Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM.