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Sleep: Facts

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Why do we need sleep?

Man in Pajamas with a Candle

We all know those times when we just can't stay awake any longer. Our eyes get heavy and we want sleep more than anything. We also know that after a good night's sleep we feel better, have more energy and can deal with daily challenges more effectively. But scientists don't really know why we sleep or even what sleep actually is. They continue to study sleep and to find out some important things that happen to our bodies when we get enough sleep and also when we don't.

All animals need sleep. Insects, people, birds, sharks, whales and squirrels require sleep. Sleep is important to the body's ability to rejuvenate and make repairs. During sleep, the body repairs cells which allows for healing from injuries and illness.

Ball Thrown at Persons Head

During the act of sleeping, growth hormones are released into the body. Children who are still in their growth years need sleep in order for growth and development of muscles, bones, and brain cells.

Another thing that happens during sleep is that the brain sorts out the day's activities. This helps the brain to remember things we learn, to deal with problems that we had during the day and to keep us in a state of overall well-being. Without a good night's sleep we can feel cranky. Some people cry more easily. Most everyone has slower reaction times. Lack of sleep can even cause us to have poor memories. People who lack sleep are more likely to have accidents or become sick.

In studies on animals, those that were denied the opportunity to sleep didn't live as long as animals that were allowed to sleep as much as they desired.

How We Sleep

Child Sleeping

Our brains have a gland known as the pineal gland. It is located almost in the center of your brain. When the sun goes down, this gland is stimulated to send out a body hormone known as melatonin. Melatonin causes our bodies to relax and to feel ready for sleep. Interestingly enough, our bodies can be fooled into thinking it is daylight by indoor lighting and melatonin can be found in some foods we eat. So our bodies must also be regulated by other factors or we could be awake or asleep simply by changing the lights or eating certain foods.

Body Clocks

Clock with a smile

All of us have two different internal clock systems that drive our sleep times and our awake times. Our bodies have one clock that says we should sleep after being awake for a long period of time. For most people, it causes us to be awake when it is daylight and want sleep when it is dark out. The daylight allows us to be able to see so we can do things all the things that keep us busy. Because of this long period of wakefulness, we then need sleep when the day is over. By this time, it is usually dark. This is called sleep/wake homeostasis.

The other internal clock is known as circadian rhythm. This rhythm causes a series of wakeful times followed by times that we are likely to be drowsy. This takes place off and on all day long. This is different than the need to sleep at night and to be awake during the day. In adults, the strongest need for sleep usually occurs during the hours of 2:00 - 4:00 in the early morning and again between 1:00 - 3:00 in the afternoon. These hours of needing sleep vary by a person's age, level of activity, foods eaten, and other personal behaviors and routines.

Stages of Sleep

Man Sleeping in Bed

Our sleep may seem like one big long night of nothing, but the truth is, we have several stages of sleep that take place. For the majority of our sleep period, we fall into the NREM sleep. This is known as Non Rapid Eye Movement. In the beginning of NREM, we are very light sleepers and are between being awake and asleep. People can talk to us, we will probably answer, and we may even remember the things going on around us. This is Stage 1.

In Stage 2 of NREM, our body temperature drops and we are unaware of things going on around us. We've all fallen asleep during a movie or television program and been surprised that we "missed" important events of the story. Our heart rate and breathing are very regular during this stage.

By the time we have reached stage 3 and 4, our blood pressure has dropped, our breathing is slowed, we are very relaxed and we are in the deepest part of sleep. This allows body healing and growth hormones to be released while also restoring our body's energy.

REM sleep or Rapid Eye Movement occurs only a small portion of our sleeping time. It is during this stage that dreams occur. Our eyes actually move back and forth while in REM and thus the name. Muscles are shut down during this phase and we become the most relaxed. Breathing and heart rates can change often during this stage. During REM, our brains reorganize information that we have come in contact with during the previous day. Memories are sometimes relived in unusual ways and the things we learned are committed to long term memory.

The average person shifts in and out of REM and visits all of the other stages many times during a night's sleep.

How Much Sleep We Need

Grandpa Sleeping in a Recliner

The amount of sleep a person needs can depend on a lot of things. Females actually need more sleep than males. The amount of sleep needed also depends on a person's age. The younger we are, the more sleep we require. Newborns spend most of their day asleep. They can sleep anywhere between 14 to 17 hours per day. As we grow older, we can get by with fewer and fewer hours of sleep each day. School aged children need 9 - 11 hours of sleep per day while Grandma and Grandpa only need about 8 hours.

Boy Sleeping at Desk

Teenagers are the most specific group when it comes to sleep. While they can get by on 8-10 hours of sleep, they need this sleep during a different block of time than most other people. Their circadian rhythm seems to tell them to stay up later and to sleep later. This can interfere with school schedules, sports, homework, and after school activities or jobs. Because of this, they are often sleep deprived. They try to get by on the schedule that has been given to them, even though their body wants something else.

Take a look at this chart from The National Sleep Foundation to see how much sleep you should be getting. (click on the blue and orange chart you find on that page)

Improving our Sleep

Parent Reading with Child

Getting enough sleep is important to our health. Many health issues can be related to lack of sleep. But how do we improve our sleep? Getting into a routine for sleeping is one good way to make sure that we go to sleep, stay asleep and get the rest we need. It can begin by simply finding a comfortable place to sleep.

Some things that may help people sleep better are to avoid electronic devices in the hour just before bed. Don't text, watch TV or play video games right before bedtime. The lights from the screens can stimulate parts of the brain in such a way that it has a hard time "turning off" to go to sleep. A more relaxing routine of reading, a warm bath, quiet time or even soft music can help the body to shut down brain activity and allow sleep to come easier.

Man Eating Spicey Food

Exercise has been shown to lessen the amount of time needed to fall asleep. This may be related to hormones produced by the body during exercise or even the fact that the body gets tired and ready for rest during a routine of exercise. Exercising just before bed, however, has often proved to make sleeping more difficult, so exercise earlier in the day.

Certain foods can interrupt sleep. Spicy food has been known to cause stomach discomfort just when the person is ready for sleeping. Foods containing caffeine such as cola, coffee, tea, energy drinks, and yes, even chocolate may be too stimulating for the sleep process.

No Noise Sign

Here are a few additional tips that may help to improve your sleep patterns:

  • keep a constant schedule - go to bed and get up about the same time each day.
  • don't lay awake in bed for long periods - not before you go to sleep and not in the morning when you wake up - get up and do something else.
  • cooler room temperatures will help you stay asleep.
  • try to get a little bit of sunlight each day - this helps regulate the body clock.
  • avoid a noisy environment where you plan to sleep.


Boy at a Desk with a Dog

It was thought for a long time that dreams only occur during REM sleep. But REM sleep isn't the only time that we dream. During REM our dreams are the most vivid. We can dream up to two hours every night. But what are dreams really? Scientists are still trying to determine exactly why we dream and what purpose they have in our lives. Studies suggest that dreams actually help us to remember things that we have learned during the wakeful parts of our day. It may also be that dreams help us to deal with stress in our lives by helping us to practice how we will handle stressful situations. Dreams often have randomness in the way they take place; jumping from one event or location in an unreal fashion. The events may have unusual aspects that represent unreal and fantasy-like parts to them. This may be our brain's attempt at tying events from our day together into one dream. The brain may be sorting and uncluttering its contents similar to when you clean your desk at school. It sorts similar, but not identical, events into one dream. We don't usually notice this irrational dream story line until we are awake and are thinking about it or telling others about the dream. We may even be surprised to find people we have not had contact with for a long time in our dreams. Those people are often there because we had some type of encounter with a memory of them in our wakeful day - even if we were unaware. For example, you might see a restaurant while riding in the car where you had dinner with your cousin months ago. Although you are not really aware of this memory recall, the cousin appears in that night's dream. Dreams have been given credit for telling the future and for seeing events through other people's eyes. Although there is no real proof that either of these is possible through dreams. Some people are even aware that they are dreaming and have learned to control the events of a dream.

Boy Dreaming about a Test

Nightmares are a scary version of dreams and can be brought about by some type of stress in the person's life. These dreams can seem more real to the person and often include smell, taste, pain, and loud sounds which rarely appear in standard dreams. Fear is a predominant emotion in nightmares.

People who are unable to dream or who do not get enough sleep to get to the dream stage have been found to have more problems with coordination, concentration, weight gain, memory and their overall emotions and mood. Lack of dreaming, more than a lack of sleep, may cause severe depression.

Sleep Disorders

Dreaming about Sheep

Many people have difficulties going and staying asleep. These problems can be just a temporary thing resulting from a short period of stress, a stressful event, too much stimulation just before bed or even illness or pain. But long term sleep problems are called insomnia. Insomnia can cause other health related issues including weight gain, heart problems, diabetes, high blood pressure, and poor memory. Some studies find that hyperactivity has been found in people who lack enough sleep. Becoming ill due to a weakened immune system mean that colds, flu, even pneumonia may also be linked to a lack of sleep.

Sleep Walking

Other sleep disorders include these unusual behaviors:

  • Sleep-eating disorders - while sleeping, the person will hunt down food in the house and eat, sometimes excessively, which can cause weight gain for which they have no explanation.
  • Night terrors - often children experience this problem which includes screaming and fearful behavior while they are fully asleep and usually have no memory of the event upon waking.
  • Sleepwalking - a person is asleep, but gets out of bed and tries to function as if awake. Some of their behavior during a sleep walking episode can seem odd or strange to others.
  • Snoring - a loud vibration of the soft tissue in the back of the mouth. It prevents the snorer from restful sleep and can have the same effect on others around them due to the disruptive sound of snoring.
  • Narcolepsy - randomly episodes of sleep during the day. This is a brain related problem in which the sleep/ wake cycles are not regulated well. In some people, they have "sleep attacks" and can fall asleep suddenly.

Jet Lag and Time Changes

Woman with a Plane Ticket

Because we can travel between time zones of the world at such a fast pace these days, jet lag is one of the most common causes of sleep deprivation. Jet lag creates a disruption in the body clock and circadian rhythms. When we travel by airplane, also called jet travel, we are able to move rapidly to a time zone that is later or earlier than the one we left. Our body might think it is seven in the evening because that is the time it would be if we were at home. But, because we have traveled to a new time zone, it might be midnight in the new location. So we are wide awake and not ready to be asleep for several more hours. Then when we need to wake up the next morning in this new time zone, we are short on sleep.

Or we might have traveled to an earlier time zone where it is three o'clock in the afternoon. But our body still thinks that it is seven in the evening. So when we stay up until it is an appropriate bedtime in the new place, we have actually been awake for many extra hours. This trying to link up the day with what time it feels like and what time it really is can cause us to stay up for many more hours to be with family, friends or coworkers. And again we are short on sleep. This can be an even greater problem if the actual time is seven, eight, twelve hours, or more behind or ahead of the body's clock and the new location. It can take days for the body's rhythms to catch up to the new place. About that time, it will probably be time to go home and the jet lag starts all over again.

Time Zones

Each fall and each spring many states in the United States and several other countries around the world change the clock time by an hour to make use of daylight hours. This is called setting the clocks for Daylight Saving Time (spring) or going back to Standard Time (fall). This too, can mess up circadian rhythms for several days after the time change.

Jobs With Night Hours

Doctor Listening to Heartbeat

There are a lot of people, such as doctors, nurses, hospital workers, police, firefighters, and many others must work during the night when the rest of us are asleep. This might not sound like a problem because they can sleep when the rest of us are awake, right? Well, not really. Circadian rhythms, sunlight, the sound of the garbage truck, the mailman delivering a package, a neighbor mowing the lawn and other daytime sounds make it hard for night workers to go to sleep and stay asleep during the day. According to studies, night workers try to make the best of it, but they never fully adjust to nightshift work and are usually sleep deprived for part of the day. It is hard for people to catch up on sleep when they fall behind. For example, if someone misses two hours of sleep it is hard to cure by simply sleeping for two hours. A good full night’s sleep is the only way to solve the problem.


Boy Yawning

Yawning is an unusual behavior, don't you think? We stretch the muscles of our face, sometimes we let out a funny sound, we breathe in a deep breath and then let it out. Everybody does it, including animals. But what is it? Science isn't sure. What we do know is that we take a deep breath and let it out. This may be our body's signal to do just that. Maybe we have been sitting idle for a very long time and breathing very shallow. By taking in a deep breath we bring in more oxygen and let out lots of carbon dioxide. Maybe the lack of oxygen, or the build-up of carbon dioxide was the sign. It really has nothing to do with being tired, although being tired can cause us to take shallow breaths. Sometimes watching others yawn will also get us to yawning - so how does that work? To learn more about yawning, visit kidshealth.org.


Bear Hibernating

Hibernation (and variations of it) is a type of sleep that many animals participate in during the winter months. Their body temperature drops a lot more than during regular sleep, their breathing slows way down, and they may need long periods of actual sleep once they come out of hibernation because they will be sleep deprived. Some animals are difficult to wake during a hibernation period and may even appear to be dead.

Body systems shut down in many hibernating animals so that they don't need to eat, poop, or pee. Others, especially small animals, will wake for periods of time to snack on food that they have stored for just that purpose. Then it's back to sleep.

So why do they hibernate? For many it is difficult to find food when the ground is covered in snow. Hibernation allows them to conserve body energy which means that they don't need as much food. Just as regular sleep is difficult to explain, hibernation is also. Some animals hibernate and some do not. Bears, frogs, mice, ground squirrels, skunks, bats, and most reptiles sleep during the winter in one form of hibernation behavior or another.

The West African Lungfish can survive a periods of drought by digging a burrow into the mud where it creates a mucous type of sack to live in. It looks like a dried up leaf but that allows it to survive summer similar to a hibernation. When water returns to the area, the lungfish sheds the sack and it returns to normal. It can endure this state for as much as three full years. Learn more about the lungfish at National Geographic.

Fascinating Facts About Sleep

  • A dolphin only sleeps half a brain at a time - one half of its brain sleeps while the other half is awake and then it switches sides.
  • Before lightbulbs were invented, people slept an average of an hour and a half longer per day than we do now.
  • It is estimated that sleep related accidents and errors are responsible for 25,000 deaths and 2,500,000 disabling injuries each year.
  • More people are in sleep deprivation related car accidents than in alcohol related car accidents.
  • Stress in the biggest cause of a lack of sleep.
  • Blind people often have sleep problems because their bodies do not respond to sunlight stimulus.
  • You spend a third of your life sleeping.
  • You can survive longer without food than you can without sleep.
  • Scientists don't really know if animals dream.
  • Humans are the only animals that avoid sleep on purpose.
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