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During sleep, the brain is highly active, processing what has been learned during the day and regenerating the immune system.
February 21, 2025
Sharon Burbat
Those who do not sleep or sleep too little are exhausted, tired, and easily irritable during the day. The consequences of lack of sleep are no secret. But how much sleep does a person really need, and can you also sleep too much?
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We spend about a third of our lives sleeping. It is indispensable and a prerequisite for health and performance. There are people who manage with five hours of sleep and others who only feel truly rested after ten hours.
Eight hours of sleep are often recommended. However, there is no universal answer to the question of optimal sleep duration. Numerous studies have shown that the majority of adults cope well with seven to nine hours of sleep, but the differences are very large individually, ranging from three to twelve hours.
In women, the need for sleep can also change with the phases of their cycle. Some suffer from sleep disturbances, daytime sleepiness, or a generally increased need for sleep in the phase after ovulation. Consistently sleeping less than five hours a night - studies suggest - is harmful to health.
The rule of thumb is: Anyone who can work concentrated for a long period of time during the day, even when sitting, without becoming drowsy, has found their personal sleep quota. By the way: The sleep rhythm changes throughout life, and the need for sleep continuously decreases. Newborns sleep 14 to 17 hours a day, teenagers need eight to ten hours, and sometimes seniors only need six to seven hours.
Our internal clock ticks in a day-night rhythm, and our social life is set for 9-to-5 jobs. However, not everyone has regular working hours, and even those who do often have problems due to constant availability, making it difficult to relax and really switch off.
It almost sounds paradoxical, but analyses have shown: People who work a lot also sleep less. Those who work a lot often have sleep disorders. But to be productive and creative, we need one thing above all: sleep.
© Ketut Subiyanto
Those who work a lot often suffer from sleep disorders.
Insomnia resembles the influence of alcohol consumption in its effect. Someone who doesn't sleep for 24 hours is similarly impaired in their mental abilities as someone with a blood alcohol level of 0.1 percent. Those who sleep only five hours for four nights in a row make as many mistakes as someone with a blood alcohol level of 0.06 percent.
Too little sleep makes you sick. During sleep, the brain is highly active, processing what has been learned during the day, separating important from unimportant, regenerating the immune system, and strengthening memory.
Persistent lack of sleep can even have long-term negative effects on health. The risk of hypertension, cardiovascular disease, obesity, and depression increases.
If you sleep significantly longer than usual, you may not feel refreshed and rested upon waking up, but quite the opposite: still tired.
Studies have shown that too much sleep over a longer period of time can have similar effects on cognitive performance as sleep deprivation. There is also a recognized connection between too much sleep (more than ten hours per night) and the metabolic syndrome.
Long sleepers had higher blood fat levels (triglyceride levels) compared to people who slept six to eight hours a night. Women had a larger waist circumference, lower HDL cholesterol levels, and higher blood sugar levels. Both too much and too little sleep - researchers suspect - affect the balance of hormones that regulate hunger. This leads to increased appetite.
The link between sleep and mood is very close. The result of a data analysis by the German Depression Aid Foundation shows that too much sleep can lead to a worsening of depressive symptoms and it may therefore be sensible to limit the length of sleep to a maximum of eight hours to counteract symptoms of depression.
Finding out your personal ideal sleep duration is actually quite easy, although time-consuming. Therefore, carry out "the test" preferably during vacation or holidays.
Go to bed at the same time every evening and do not set an alarm clock. Get up when you feel rested and awake. Note how many hours you have slept per night.
The first night is not very significant, as you may have a sleep deficit to catch up on. From the log, you can then deduce well what your personal sleep requirement is and how many hours you should sleep even during a regular workweek.
