Deep Sleep – Why Is It So Important?

Since deep sleep is so essential for our well being, it is good to know what exactly is deep sleep, how it happens, why it’s necessary for our brain and finally how to get more of it. Let’s dig into it.

Written by:


, Sleep Researcher
Last Updated: Thu, October 3, 2019
Fact checked by:

Marko Jevtic

, Sleep Specialist

Getting a good night’s sleep is essential for maintaining good health. We have all heard that we should get somewhere from seven to nine hours every night to get the best benefits from sleeping. But while sleep duration is very important, it is not the only solution to feeling well rested in the morning. The quality of sleep plays an important role as well. That’s why some people wake up tired, even though they supposedly had enough sleep that night.

When you think about the quality of sleep, it usually refers to spending sufficient time in the deep stage of sleep. Scientists have found that people who spent less time in deep sleep have a higher probability of rating that night’s sleep quality as low, compared to people who spent more time in this stage.

Time spent in deep sleep decreases with age, and while healthy people in their 20s spend around 20% in this stage, it falls to about 10% in people in their 50s and as low as two to five percent in people who are more than 70 years of age. Less deep sleep is connected to decreased mental capabilities, weakness and rarely feeling well rested after waking up.

Since deep sleep is so essential for our well being, it is good to know what exactly is deep sleep, how it happens, why it’s necessary for our brain and finally how to get more of it.

What Is Deep Sleep

Deep sleep is named after the increased inability of a sleeper to perceive external stimuli during this stage. When you find it hard to wake somebody up, even if you are yelling or touching them, know that they are in the deep stage of sleep.

Waking up in this stage produces a phenomenon called sleep inertia. It’s that familiar feeling of disorientation, grogginess, and irritation. To avoid this, and feel refreshed after waking up, try to track your sleep and set your alarm to wake up during light stages or REM stage.

Deep sleep refers to a stage of sleep with slowest brain waves recorded. It is sometimes called slow-wave sleep, Stage 3 of non-REM sleep, N3, or delta wave sleep. It is essential for memory consolidation, maintenance of your brain, and reparation of your muscles and other tissue.

Stages of Sleep

Sleep consists of two phases, non-REM (NREM) and rapid eye movement (REM) sleep. We spend around 75% of our time in NREM stages of sleep, and about 25% in the REM stage. Each sleep cycle consists of both of these parts, and it usually lasts 90 to 120 minutes. We experience three to six cycles each night.

NREM sleep consists of three different stages:

Stage 1 – First stage is the transition between being awake and asleep. It only lasts several minutes; our muscles start to relax, breathing, heart rate, and eye movement all slow down.

Stage 2 – It is a light sleep stage, that happens before you fall into deep sleep. You usually spend most of the time sleeping at this stage. Your heart and breathing rate is even slower, your muscles continue to relax, and your eye movement is completely stopped. Your brain waves slow down, but there are occasional electrical bursts. All the tossing and moving around happens in this stage, and it is vital for maintaining the circulation through your entire body. If you stay motionless for too long, it leads to a lack of oxygen and nutrients in some parts of your body, and that can lead to tissue damage.

Stage 3 – It is a stage of deep sleep crucial for brain and body maintenance, and feeling refreshed in the morning. It usually lasts longer in the first part of the night, and then it lasts longer later on. That way your brain does the necessary housekeeping right away, and it avoids spending too much time in deep sleep close to morning, as that increase the chances of waking up during deep sleep and feeling groggy.
Your heart and breathing rate are slowest in this stage, and your muscles are very relaxed. The growth hormone is essential for growth and development, and it is released during this stage. That is why deep sleep is crucial for children, and they usually spend a lot more time in this stage than adults.
Delta brain waves that characterize this stage are of high amplitude and low frequency. This is the period when your neocortical neurons can rest.

REM stage – Usually happens every 90 minutes. It is a stage when your breathing and heart rate increase, your eyelids are closed, but your eyes are going from side to side, and your brain waves are mixed. Dreaming mostly occurs during this stage, and your muscles are shut down, so you don’t act out while dreaming and hurt yourself. It’s been observed that depressed people usually spend more time in this stage, so antidepressants work to regulate REM sleep.

The Importance of Deep Sleep

If you have ever missed a night of sleep, you know that the following day you’ll feel moody, less focused and will have decreased learning abilities. That can affect your work performance and overall quality of life. After the period of sleep deprivation, we try to make up for the lost sleep. That means that we will sleep for a more extended period, but what’s more interesting is that it affects sleep stages as well. During our rebound sleep, the percentage we spend in deep sleep increases a lot, which shows the importance of this stage.

Deep sleep is crucial for the consolidation of memory. That’s why individuals who have insomnia often have impaired memory, and don’t perform as well on memory tests. The current model for long-term memory storage relies on interactions between the hippocampus and neocortex. Deep sleep is crucial for maintaining the learning efficiency of your brain, so if you have a big test coming up, don’t sacrifice sleep to stay up and study, as it can be counterproductive.

Deep sleep is needed as it is the time when our brains do the necessary housekeeping. Don’t forget that our minds work without stopping, so time to repair all the damage all around our body is of great importance. For a long time, scientists weren’t quite sure how our brains get rid of all the harmful substances that can be very dangerous if they get accumulated. A few years ago, research had finally shed some light on how it happens, and now we understand more about this phenomenon.

How Does Your Brain Get Rid of Harmful Substances

Our brains don’t have the lymphatic circulation, so it wasn’t quite sure how it got rid of all the waste that is produced during cell metabolism. In the 2012 study, Nadergaard and a team of researchers first described the glymphatic system used to remove all the toxic substances and harmful proteins from the brain. Cerebrospinal fluid (CBS) is pumped in the brain during our sleep, and it washes away the waste. It goes through the brain interstitial space, and it is then removed from the brain via blood vessels.

A 2019 follow-up study showed that the glymphatic system is active during the deep stage of sleep. The researches have induced delta waves by giving six different types of anesthesia regimens to mice. They observed that the combination of ketamine and xylazine worked best to mimic the deep sleep stage. It closely replicated the slow and steady brain waves, as well as hearth and breathing rate that occurs during the third stage of non-REM sleep. The team observed this state to be optimal for glymphatic system functioning, concluding that the glymphatic system is most active during deep sleep.

The accumulation of proteins such as beta-amyloid and tau are correlated with Alzheimer’s disease, so scientists have been speculating that disruption of sleep can impair the glymphatic system, leading to the accumulation of these proteins and inducing Alzheimer’s disease. This is consistent with current knowledge that sleep deprivation increases the chances of getting Alzheimer’s disease.

Deep Sleep Disorders

Not getting enough deep sleep can affect many parts of our lives, but there are also some deep sleep disorders and parasomnias that need to be treated by professionals. These include:

Sleepwalking, night terrors, and nocturnal enuresis most commonly happen in children. If your child is experiencing any of these, you should consider taking them to the doctor. Deep sleep is essential for children as it is the time when growth hormone is released. If there are any disturbances in this stage, you want to try and remove them right away.

How to Get More Deep Sleep

Spending more time in Stage 3 of non-REM sleep can be a little tricky, as there is no definite way to increase only deep sleep. Most medications used to treat sleep disorders increase the duration of sleep, but it is mostly on account of light sleep. Spending more time in light sleep can, in fact, lead to more deep sleep, so it is a good start. Before sleep medication, we always suggest an adjustment of lifestyle to promote better quality sleep. You can try:

Remember that time spent in deep sleep varies between individuals, so good night’s sleep for a 50-year-old might be a terrible night for a 20-year-old. The depth of sleep also varies, so some people naturally sleep deeper than others. But that doesn’t have to mean that they have more sleep benefits. It’s also important to know that there is no such thing as too much deep sleep, so practice good sleep hygiene and sleep well!


Sleep Related

Was this post helpful?

+ posts

Dusan is a biologist, a science enthusiast and a huge nature lover. He loves to keep up to date with all the new research and write accurate science-based articles. When he’s not writing or reading, you can find him in the kitchen, trying out new delicious recipes; out in the wild, enjoying the nature or sleeping in his bed.

Leave a Reply

Your email address will not be published. Required fields are marked *