Why Do We Sleep?

Waking up from a restful night of sleep is a great feeling. The body is restored, relaxed, and ready to start the day! But why do we need to sleep and why is it so critical for our health?  

Learn more about the ways that sleep contributes to optimal health.  


Why do we need sleep? 

Sleep is essential. Like food and water, without sleep, humans wouldn’t be able to survive. For a number of biological reasons adequate sleep is required to be healthy. Sleep allows our cells to regenerate and repair themselves, facilitating tissue growth, muscle healing, hormone release, and protein synthesis. It also provides time for neurons in the brain to reorganize and get rid of waste from the central nervous system. This affects many facets of brain function including memory, concentration, problem-solving, focus, creativity, learning, and more.  

Sleep is critical for maintaining a healthy weight since it controls hunger hormones that help to increase feeling full after eating. Not getting enough sleep can result in an imbalance in these hormones which may lead to feeling hungrier and gaining weight. If all these reasons aren’t enough to pursue healthy sleeping habits, sleep has also been shown to support heart health, insulin function, and the production of cytokines which are needed to develop a strong immune system.   

What Happens When We Sleep?  

Once a person falls asleep, the body cycles through four specific stages. These sleep stages are typically repeated 4 times with each cycle lasting from between 70 to 120 minutes. The following is a description of each sleep stage in the cycle and what happens to the body during it.   

Stage 1: Non-REM Sleep 

This first stage is also known as “light sleep”.  It characterizes the transition between being awake and the moments after falling asleep. As the body enters this stage, muscles begin to relax and the heart rate, breathing, eye movement, and brain waves begin to slow down. This is a quick stage in the cycle that typically only lasts for 7 minutes.   

Stage 2: Non-REM Sleep 

While still in light sleep, this stage is usually the longest of the four in a sleep cycle. Stage 2 is the last point before the body enters deep sleep. Breathing slows even further, along with the heart rate and more muscle relaxation. The brain waves will spike momentarily and then remain slowed down. Finally, all eye movement will stop and the body temperature will decrease.   

Stage 3: Non-REM Sleep 

This is the stage where deep sleep finally begins. Muscles activity and eye movement stop completely, and the brain waves, heartbeat, and breathing are at their lowest levels. Sleep in this stage becomes restorative and it is during this stage that most of the health benefits listed above begin are captured. Neglecting this sleep stage means missing out on the health benefits of sleep and can lead to a groggy feeling in the morning.   

Stage 4: REM Sleep 

This stage typically occurs about ninety minutes after falling asleep. The heart rate will increase along with breathing. Also known as the “Rapid Eye Movement” stage, it’s easy to tell when this stage is reached because the eyes will start to move quickly from side to side under the eyelids. It's at this point in the cycle that dreams occur and memory consolidation happens. This is the process of converting newly learned experiences into long-term memories. The limbs typically also become paralyzed during this stage to stop sleepers from moving around in response to their dreams.   

These four stages continue to repeat throughout the night until waking.   

How much sleep is needed? 

Babies and younger children need more sleep than adults because their bodies are experiencing rapid development and growth. This is why infants and toddlers require 14-17 hours of sleep per day, resulting in both regular sleep at night as well as frequent day time naps. By the time children reach the ages of 6-13, only nine to eleven hours of sleep is needed per day. As the body gets older, growth slows down and then stops which means adults don’t require as much sleep to stay healthy. The average adult only needs between 7 - 9 hours of sleep per day to achieve the best health benefits. 



sleepfoundation.org - why do we need sleep 

sleepfoundation.org - how much sleep do kids need 

healthline.com - what happens when we sleep 

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