Pando Hall/Getty Images
The average adult needs 7 to 9 hours of sleep a night. See more sleep pictures.
In order to answer this, let's look at some basics about sleep. The amount you need decreases with age. A newborn baby might sleep 20 hours a day. By age 4, the average is 12 hours a day. By age 10, the average falls to 10 hours a day. Senior citizens can often get by with 6 or 7 hours a day. And most adult people seem to need 7 to 9 hours of sleep a night. This is an average, and it is also subjective. You, for example, probably know how much sleep you need in an average night to feel your best.
You know you feel great after a good night of sleep. But, why is that? Does anything important happen during sleep? Growth hormone in children is secreted during sleep, and chemicals important to the immune system are secreted during sleep. You can become more prone to disease if you don't get enough sleep, and a child's growth can be stunted by sleep deprivation.
No one really knows why it is that we sleep, but there are all kinds of theories, including these:
- Sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells, and so on.
- Sleep gives the brain a chance to organize and archive memories. Dreams are thought by some to be part of the process.
- Sleep lowers our energy consumption, so we need three meals a day rather than four or five. Since we can't do anything in the dark anyway, we might as well "turn off" and save the energy.
- Sleep may be a way of recharging the brain.
Why do I need sleep?
A good way to understand why you sleep is to look at what happens when we don't get enough:
As you know if you have ever pulled an all-nighter, missing one night of sleep is not fatal. A person will generally be irritable during the next day and will either slow down (become tired easily) or will be totally wired because of adrenaline.
Photo courtesy Dreamstime.com
- If a person misses two nights of sleep it gets worse. Concentration is difficult and attention span falls by the wayside. Mistakes increase.
- After three days, a person will start to hallucinate and clear thinking is impossible. With continued wakefulness a person can lose grasp on reality.
A person who gets just a few hours of sleep per night can experience many of the same problems over time.
It only takes three days of sleep deprivation to cause a person to hallucinate. Obviously, if you were to go for a longer period of time, the symptoms would worsen and in time, would most likely prove fatal. Rats forced to stay awake continuously will eventually die, proving that sleep is definitely essential. Unless you were being forced to stay awake, you'd probably fall asleep before something as drastic as death could happen.
It's interesting to know that some people can function on very little sleep if necessary. A portion of a Navy SEAL's rigorous training program is a good example of this phenomenon. During what is commonly called "Hell Week," the trainees must engage in highly physical activities for about six days - all of their hard work is accomplished on about 4 hours of sleep for the entire week!