Sleep, sleep, sleep. We all need it, and most of us say we don't get enough of it. What's the big deal with sleep anyway? It's such a strange habit. You lie your body down for hours at a time so you can fall into some catatonic state where you aren't aware of what's going on around you. Sleep is something humans and animals alike have done for all of eternity, yet it remains vastly understudied. In fact, the first major breakthrough in the study of sleep came in 1953 when Eugene Aserinsky discovered REM sleep while studying his eight-year-old son at the University of Chicago. So why is sleep so important? What does it do for us? What happens when we don't get it? Inquiring minds want to know!

What Is Sleep and Why Do We Need It?

The Oxford Dictionary defines sleep as "a condition of body and mind that typically recurs for several hours every night, in which the nervous system is relatively inactive, the eyes closed, the postural muscles relaxed and consciousness practically suspended." Our bodies regulate sleep in a similar fashion to how it governs breathing, eating, and drinking. When our body says we're hungry, we eat. If we're thirsty, we drink. We breathe without conscious thought, and if we stay awake too long, our body floods itself with hormones to lull us into sleep. This automatic regulation indicates that sleep is vital to our overall well-being. We cannot survive without food, water, or oxygen. Therefore, it stands to reason that we would not survive long without sleep either. 

What Happens When We Sleep

It is thought that sleep gives both the body and mind a chance to enter into a process of recovery. The body undergoes many changes while sleeping. It reacts differently depending on what stage of sleep you are in. As you may already know, the sleep cycle is segmented into four stages, with each cycle lasting approximately 90 minutes. 

Stage 1 (Transition) - The act of falling asleep, usually taking between 10 - 15 minutes.

Stage 2 (Light Sleep) - Entered after transitioning into sleep. A deeper state of relaxation with some spikes of electrical activity in the brain.

Stage 3 (Deep Sleep) - Also known as restorative sleep. During this stage, your breathing and heart rate are at extremely low levels, and your muscles enter into a state of deep relaxation. 

Rapid Eye Movement (REM) - Considered the dream state, here the brain wakes up and functions almost as if we are awake. Breathing and heart rate speed up, and the eyes move rapidly back and forth underneath the eyelids. 

The question of what happens as we experience these sleep cycles is closely tied to the question of why we sleep. Scientists have been studying these questions for years with no conclusive findings. However, three theories are generally accepted as answers to the question of what goes on with the body while sleeping.

The Energy Conservation Theory

The cornerstone of this theory is that we sleep to conserve our energy. Our caloric needs are drastically reduced when sleeping, therefore requiring less energy than staying awake full-time. This is backed by studies that show our metabolic rate drops by about 15% during the night, and research has shown that sleeping 8 hours produces a daily energy savings of 35%. By entering into a hibernation of sorts, sleeping conserves energy when it is not an optimal time to be active and functioning.

The Restorative Theory

According to The Restorative Theory, sleeping gives our body rest time, allowing our cells to grow and repair themselves. We are very active while awake, which causes wear and tear on our bodies. Evidence suggests that our body takes that opportunity to rejuvenate itself while we sleep, including muscle growth, tissue repair, and protein synthesis. It is also true that the majority of growth hormones are released into the body during deep sleep, also known as slow-wave sleep

The Brain Plasticity Theory

Brain plasticity is the ability of the brain to change and adapt based on certain experiences. It is a phenomenon that is not yet well understood but has garnered many studies in recent years. Scientists that put forth this theory believe sleep allows your brain time to reorganize. During sleep, your brain turns short-term memories into long-term memories. It also erases or forgets any information that is not needed to keep your nervous system from becoming too cluttered. Many mental skills we depend on to get through our day are affected by sleep, such as decision making, learning ability, focus, concentration, problem-solving, and creativity. Not getting enough sleep indeed inhibits brain function. Anyone who has ever uttered the phrase "I'm too tired to function" can certainly attest to that. 

Sleep Deficiency

Sleep deficiency is a broader concept than sleep deprivation. Being sleep-deprived is a condition that occurs if you don't get enough sleep. A sleep deficiency occurs over time and is caused by one or more of the following reasons:

  • Not getting enough sleep
  • Sleeping at the wrong time of day (out of sync with your body's natural rhythm)
  • Poor quality of sleep
  • Having a sleep disorder

Based on the phases of sleep detailed above, there are two types of sleep: REM and non-REM. Most people cycle in and out of REM and non-REM sleep several times throughout one sleep session. How well you feel when awake is directly related to not only getting the proper amount of sleep but also enough of both types of sleep. 

Your need for sleep is based on your internal body clock, also known as your circadian rhythm. Your circadian rhythm roughly follows our normal 24-hour day and affects how well your body functions throughout that day. Every cell, tissue, and organ is tuned to it, and if you are not getting enough sleep, or sleeping out of sync with your internal clock, you may find yourself moving through your days feeling tired and sluggish. 

The best way to circumvent this problem is to practice good sleep hygiene. Going to bed and waking up the same time every day, putting your electronics away an hour before bedtime, eating healthy, and getting enough exercise are all ways you can improve sleep quality. For more on this, check out our article on Natural Ways to Get Better Sleep

How Much Sleep Do You Need?

Most experts agree that you should be getting anywhere from 7 - 9 hours of sleep every night, but it varies from person to person. Some feel excellent on only 6 hours while some (especially athletes) may function better with 10. It's good to note that our sleep requirements change throughout our lives. The chart below is based on the recommendation of the American Academy of Sleep Medicine (AASM) and has been endorsed by the American Academy of Pediatrics (AAP). 


Recommended Amount of Sleep

0-12 Months

12 - 16 hours per day (including naps)

1 - 2 years

11 - 14 hours per day (including naps)

3 - 5 years

10 - 13 hours per day (including naps)

6 - 12 years

9 - 12 hours per day

13 - 18 years

8 - 10 hours per day

Adults 18+

7 - 8 hours per day

Looking at this chart makes sense that the younger a person is, the more sleep they need, especially if you revisit the theories of what goes on when one is asleep. Infants, children, and teens are doing a lot of growing, requiring more sleep than adults. 


Even with all of the mystery surrounding exactly what happens to the body while we sleep, no one can deny that it's essential to our health and well-being. People who do not get enough sleep or suffer from poor-quality sleep often have trouble making decisions, solving problems, and controlling their emotions. It can affect your reaction time, inhibit your ability to finish tasks, and cause you to make more mistakes throughout your day. On the flip side, being well-rested helps you think clearly, stay calm in pressure situations, increase concentration, reduce stress, and improve your mood. We think that makes sleep pretty important!

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