How Much Sleep Do I Need? | Numbers & Recommendations

Modern life is quite intense, and people often sacrifice sleep in order to have time to get things done. Unfortunately, it is very harmful for our health, because sleep is as much important for a person as a proper diet and physical activity. Even a small lack of it can have a negative impact on mood, energy, mental acuity and the ability to cope with stress. But how long should an adult, a teenager or a kid sleep properly: 6, 7 or 9 hours? What is REM and what is deep sleep? And how to wake up refreshed and full of energy?

False stereotypes about sleep

Myth: Sleeping an hour less will not affect activity during the day.

Fact: A person may not feel very sleepy, but a lack of even 1 hour of night rest can affect the adequacy of thinking and responsiveness. In addition, even such a seemingly insignificant lack of sleep can jeopardize cardiovascular health, energy and the ability to resist infections.

Myth: The human body adapts quickly to different sleep schedules.

Fact: The body is actually capable of “resetting” its biological clock by a maximum of 1-2 hours per day without consequences. This means that after moving to a different time zone or after switching to a night shift, it may take at least a week for the body to adjust to a new life schedule.

Myth: A longer night’s sleep can relieve excessive daytime fatigue.

Fact: It’s important to understand that the quantity and quality of sleep are different things. Some people can sleep 9-10 hours at a time and still not feel rested after waking up just because the quality of their rest wants to be better.

Myth: You can get a whole week’s worth of sleep at the weekend.

Fact: It is impossible to completely make up for the lack of sleep accumulated during the work week or “pay off the sleep debt”. Such a practice can only negatively affect the cycle of rest and wakefulness, because of which on Sunday people can remain active until late at night, but it will be very difficult for them to wake up on Monday morning.

How much sleep is recommended?

To begin with, we need to understand that there is a difference between how much a person can sleep and the length of sleep actually needed for optimal functioning of the body. According to experts, on average, adults sleep 6 to 7 hours. At first glance, this may seem like a pretty good figure. In fact, it is a typical example of chronic lack of sleep.

Most healthy adults need between 7 and 9 hours of sleep per night. For children and adolescents, the figure is slightly higher. Despite the fact that elderly people should not have less than 7 hours of rest either, many elderly people suffer from insomnia. If this is the case, you should at least partially compensate for the lack of a night’s rest with a day’s nap.

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The chart below show the recommended hours of sleep for different age categories.

Age RangeRecommended Amount of Sleep
Newborns0-3 months old14-17 hours
Infants4-11 months old12-15 hours
Toddlers1-2 years old11-14 hours
Preschoolers3-5 years old10-13 hours
School-age6-13 years old9-11 hours
Teens14-17 years old8-10 hours
Young Adults18-25 years old7-9 hours
Adults26-64 years old7-9 hours
Older Adults65 or more years old7-8 hours

Interestingly, researchers at the University of California, San Francisco, found that some people have a gene that allows them to sleep six hours a night and still get a good night’s sleep. However, this gene is found in only 3% of the world’s population.

Symptoms of sleep deprivaton

The best way to figure out if you get enough sleep at night is to critically assess your condition during the day. Although people who are used to constantly “saving” on their rest may no longer remember what it is like to be really awake, to be as concentrated as possible. But there are certain signs that a person does not get enough sleep.

It is possible that you do not have enough sleep, if you:

  • need an alarm clock to wake up on time;
  • can reset the alarm clock after the bell rings for a few more minutes;
  • have trouble waking up and getting out of bed;
  • feel sluggish during the day;
  • may pass out in a meeting, in a class, or in an empty office;
  • feel drowsy while driving and after eating;
  • need at least a short nap during the day;
  • fall asleep quickly while watching TV;
  • may sleep much longer on weekends than on weekdays;
  • fall asleep within 5 minutes after you go to bed.

Consequences of sleep deprivation

It may seem that lack of sleep is not such a serious problem, and all the consequences of lack of sleep are reduced solely to daytime lethargy. In fact, scientific experiments show that lack of night rest affects a person about the same way as alcohol abuse.

Sleep deprivation is:

  • fatigue, lethargy, lack of motivation;
  • poor mood, irritability, increased risk of depression;
  • impaired brain function, problems with memory, learning and concentration;
  • reduced creativity and ability to solve problems quickly, difficulty making decisions;
  • inability to cope with stress and manage emotions;
  • impaired motor skills, increased risk of accidents;
  • weakened immune system, tendency to frequent colds and infectious diseases;
  • possible hallucinations and delirium;
  • increased risk of stroke, diabetes, hypertension, Alzheimer’s disease, some types of cancer;
  • reduced sex drive;
  • premature skin aging.
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In addition, scientists have found a direct link between lack of sleep and weight gain. Sleep-deprived people produce higher amounts of cortisol, a hormone that increases appetite.

Sleep phases and sleep quality

During rest, our brain goes through two main phases: slow and fast sleep, which alternate throughout the night. During the slow phase the brain gradually enters a state of deep relaxation. It is during this time that the main regeneration processes in the body are going on intensively. In most people, the slow phase of sleep lasts an average of 90 minutes, after which the brain enters the REM sleep phase. During this period, brain activity increases again, the heart rate increases and it is during this period that a person dreams. This phase lasts for about 15 minutes. If no waking occurs during this time, the brain enters the slow sleep phase again. During the night, the entire cycle is repeated four or five times.

That is, since the slow phase is the time when the brain gradually “shuts down” and goes into a state of deepest relaxation, waking up during this period is the most difficult and unpleasant. As a rule, either a loud sound or a jolt is required to wake a person in the deep sleep phase. In this case, it will take him a little longer to fully awaken and regain his alertness. Many people after such an awakening feel tired throughout the day, as if they never had a night’s rest.

During the REM sleep phase, awakening is much easier and quicker, since the brain is in a state almost identical to that of daytime awakening. Waking up during this period makes you feel awake, refreshed and ready for action. Therefore, the best time for waking up is considered to be the phase of REM sleep.

How to calculate the best time for waking up?

Using average data on the duration of the phases, you can create your own sleep calculator and calculate how long you need to rest in order to wake up easily in the morning. We already know that the slow-wave sleep phase lasts about 90 minutes, which means that in order not to wake up in that period, the total duration of the night’s rest should be a multiple of 90 minutes (1.5 hours). That is, if a person plans to get up at 7:00 in the morning, they should fall asleep at 11:30 p.m. The result is 450 minutes of rest, which equals five 90-minute cycles.

But this calculation should take into account the additional time needed to fall asleep. This usually takes about 15 minutes. That is, taking into account the time to fall asleep, you should go to bed at 11:15 p.m. As a result, the duration of sleep is 7.5 hours, which fits perfectly into the recommended norms of a healthy night’s rest. If a person does not have time to fall asleep before 11:30 p.m., but still has to get up at 7 a.m., then according to this theory, to wake up awake, he must go to bed between 1:00 and 2:30 a.m. Falling asleep at a different time will result in waking up in a deep phase. And you already know what this is fraught with. However, going to bed after 1 or even 2 a.m. can hardly be called correct and useful for the body.

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In addition, it should be emphasized that the duration of the slow phase of 90 minutes is an average, which in reality may not be suitable for everyone. There are people who have a slow phase duration of 120 minutes, while others have a slow phase duration of only 80 minutes. Therefore, the most accurate personal calculator can be made only after observation: one day sleep for 7 hours, another for 8.5, etc. Experimenting with different sleeping times is best done on weekends. In the end you will be able to determine your own duration of the slow sleep phase.

A variation of the method

There is another – more comfortable and faster way to determine individual sleep phases. To do this, it is necessary to remember when you went to sleep. In the morning, it is important to wake up on your own – without an alarm clock or extraneous noises interrupting your rest. After such an awakening, the person should feel awake and well rested (if everything is done correctly, the person will wake up independently in the REM sleep phase).

Now it is necessary to calculate the duration of rest in minutes and divide the resulting number by 5 (this is how many sleep cycles are considered the most useful for the body). The result is one cycle of your sleep. In order to determine the most comfortable time for waking up, you should multiply this number by the number of cycles you need. Theoretically, using such a calculator, you can easily wake up awake every day even after 6 hours of sleep. But in practice, this method will work only for the first few times. Then the body begins to suffer from chronic lack of sleep.

According to observations of experts, a 6-hour night rest without serious damage to health, you can afford not more than 1 time a week. The rest of the time you need to fit in a healthier framework of 7 to 9 hours of rest.

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