What is “normal” sleep?
A good night’s sleep is when you fall asleep quite easily, do not fully wake up during the night, do not wake up too early, and feel refreshed in the morning. Regularly having difficulty falling asleep or sleeping through the night is not normal for healthy people of any age. But not everyone needs the same amount of sleep, and quality of sleep is different in different phases of life.
Young children and older people sleep more lightly than adults and teenagers. The length of time spent in deep sleep phases changes over a person's lifetime. Babies and toddlers need to sleep a lot more than older children and adults. By the time they reach the age of five, most children have the typical sleep patterns of an adult: they are awake during the day and then sleep through the night. The amount of time spent sleeping gradually decreases until the age of 80.
Normal sleep cycles
Sleep cycles usually repeat every 90 to 110 minutes. Each cycle is made up of a sequence of different sleep phases. There are two main types of sleep:
- REM sleep
- non-REM sleep
REM is short for “rapid eye movement.” This name describes the quick eye movements that can be observed during deep sleep. When children and adults are in deep sleep their eyes move back and forth quickly but their eyelids remain closed. We only dream during the REM phases.
Onset period followed by four phases of sleep
When measuring total sleep time, sleep is considered to start when you close your eyes to fall asleep. The period between first closing your eyes and entering phase 1 is known as sleep onset.
Phase 1 is very light sleep, where you are drifting in and out of consciousness and are easily woken. In phase 2 the functioning of the brain slows down but there are still short bursts of activity.
The first two phases of light sleep make up about half of the total sleep cycle. Phases 3 and 4 are the deep sleep phases. You dream in phase 4. When this phase ends, you sleep more lightly again before a new full sleep cycle starts. Some people completely or partially wake up after the sleep cycle ends, while others stay asleep until morning.
Total sleep time ends when you wake up and then stay awake and get up.
Sleep changes as you age
There are plenty of theories about what normal sleep is and how it is affected by age. It is known that sleep onset - the time needed to enter into light sleep – increases with age. But this age-related difference is very slight: Between the ages of 20 and 80 the length of sleep onset increases by less than ten minutes on average.
The phases of deep REM sleep gradually become longer between the ages of five and nineteen. They then stay fairly stable until about the age of 60. People over 60 get slightly less deep sleep and they do not sleep quite as soundly as younger people.
For children between the ages of five and twelve, a night’s sleep of nine hours is quite normal. The average person sleeps about seven hours a night around the age of 40, and about six and a half hours a night between the ages of 55 and 60. A healthy 80-year-old will usually sleep about six hours a night. But these are all only averages: everyone needs a different amount of sleep.
Things that can disturb your sleep
Getting enough sleep is essential to your health and wellbeing. There are different ways to improve your sleep and treat insomnia.
Many things can make sleeping difficult too, like alcohol, drugs and medication. Mental or physical illness can reduce your quality of sleep just as much as stress or working shifts at odd hours. Some people's sleep is disturbed by nightly pauses in breathing (sleep apnea) or restless legs syndrome. Others wake up several times each night to go to the bathroom. During menopause many women find that their sleep is interrupted by hot flashes.
Grinding your teeth (bruxism), talking in your sleep or sleepwalking (somnambulism) can also affect how well you sleep. Nightmares can also make you wake with a start and influence how long and deeply you sleep. Jetlag is another factor that can really confuse your sleep-wake cycle for a while. Almost half of us snore. You often do not notice it yourself, but it can disturb others' sleep.
Lack of sleep not only affects your quality of life. It can also be dangerous because it increases your chances of having accidents. This makes it important to find out the underlying cause if you are regularly sleeping poorly.
Andreae S. Lexikon der Krankheiten und Untersuchungen. Stuttgart: Thieme; 2008.
Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 18th ed; 2011.
Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.
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