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If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.
Ever since researchers discovered that there were multiple stages of sleep, one of those stages has stolen most of the attention: rapid eye movement (REM) sleep. After all, REM sleep is the stage where we experience dreams, so it’s pretty interesting for researchers and non-researchers alike.
However, other stages of sleep also deserve some recognition. Deep sleep is the stage where the body repairs its tissues, builds bone and muscle, and strengthens the immune system (Patel, 2021). It also plays a vital role in the formation of memories (Zhang, 2019).
Here is what we know about deep sleep, the health risks of not getting enough, and how you can help yourself get a better night’s sleep overall.
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What is deep sleep?
Deep sleep, also called slow-wave sleep (SWS), is the fourth stage of the sleep cycle. Like all the stages of sleep, your brain and circadian rhythm (your body’s 24-hour sleep-wake cycle) control deep sleep (Institute of Medicine, 2006).
Believe it or not, most deep sleep happens in the first third of the night. During this stage, a recording of your brain’s activity would show increased high-voltage, slow-wave activity, called delta waves (Institute of Medicine, 2006).
Researchers have looked at ways of enhancing slow-wave sleep to improve cognitive abilities. A review of multiple studies using sound, electricity, and medications to increase deep sleep time in humans found that several of these methods improved cognitive abilities (Zhang, 2019).
The stages of sleep
The sleep cycle is divided into non-rapid eye movement sleep (NREM), which includes the first four stages of sleep, and rapid eye movement sleep (REM). Here are the five stages in a typical sleep cycle. You will move through these stages several times during a night’s sleep (Institute of Medicine, 2006).
The first stage of sleep begins when you are still awake. As you become drowsy and close your eyes, your brain activity changes from both alpha and beta waves to mostly alpha waves. This causes you to fall asleep (Patel, 2021).
Your body then moves into the lightest stage of sleep, called N1. Here, your brain’s alpha waves change to low-amplitude mixed-frequency (LAMF) activity. You still have muscle tone, and your breathing occurs at a regular rate. This stage usually lasts for 1–5 minutes in a cycle (Patel, 2021).
You are now falling more deeply asleep. Your heart rate and body temperature drop. Your brain starts to show long delta waves. This stage lasts about 25 minutes in the first cycle and gets longer as the night progresses. Eventually, all of your brain waves are replaced by delta waves (Patel, 2021).
This stage is deep sleep or slow-wave sleep, marked by slower frequency delta waves. It isn’t easy to wake up at this stage. If someone or something wakes you up, you will likely be very groggy for up to an hour afterward. Your body uses this stage for repairs, growth, and memory formation (Patel, 2021).
5. REM Sleep
After deep sleep, the body moves into a period of REM sleep. Your brain activity is close to the same as when you are awake, but your muscles cannot move, except for your eyes and diaphragm. This is the stage where you experience dreaming (Patel, 2021).
REM sleep behavior disorder: what is it, causes, treatment
Are there any risks from a lack of deep sleep?
Not getting enough deep sleep can have a profound effect on the brain’s ability to form memories. In one study, researchers looked at four individuals who experienced damage to the hippocampus area of the brain. These individuals also experienced a near absence of slow-wave sleep and difficulty forming episodic memories, suggesting these two activities are connected (Saletin, 2020).
Getting enough sleep overall is essential for your health. A lack of sleep can lead to far more problems than just feeling tired. Over time, sleep deprivation can lead to (U.S. National Library of Medicine, 2021):
- Decreased cognitive performance
- Increased reaction time
- Impaired decision making
- Mood changes such as depression and irritability
- Slowed growth in children
- Decreased ability to build muscle mass, fight infections, and repair cells
- Increased risk of high blood pressure, stroke, diabetes, and heart and kidney disease
How much deep sleep do you need?
Slow-wave deep sleep makes up about 13–23% of the total sleep you get each night (Institute of Medicine, 2006).
Sleep deprivation: symptoms, effects, stages
The amount of total sleep you need depends on your age, your health, and the quality of sleep you’re getting. Overall, the general recommendations for sleep are (U.S. National Library of Medicine, 2021):
- Newborns: 16–18 hours a day
- Preschool-aged children: 11–12 hours a day
- School-aged children: At least 10 hours a day
- Teens: 9–10 hours a day
- Adults (including older adults): 7–8 hours a day
Several health conditions can interfere with getting the amount of deep sleep that your body needs. These include (Karna, 2021):
- Medical conditions, such as heart failure, sleep apnea, pain, or thyroid disease
- Psychiatric disorders, such as depression or anxiety
- Environmental problems, such as excessive noise, shift work, or jet lag
- Medications that can cause insomnia or frequent waking
As you get older, your circadian rhythm changes, which often decreases your total sleep time, sleep efficiency, and time spent in slow-wave sleep. These changes are a normal part of aging (Li, 2018).
How to get more deep sleep
To get more deep sleep, you also need to get more sleep in general. There are some scientifically-backed ways to improve the quality of your sleep by making minor alterations to your lifestyle and bedtime habits.
Some small changes to your daily habits can build up over time to help you improve your sleep. Try these strategies (MedlinePlus, n.d.):
- Write down anything that is bothering you before bedtime to help calm your thoughts.
- Walk or exercise for at least 30 minutes a day, but not within two hours of bedtime.
- Avoid naps during the day.
- Stop or cut back on nicotine, caffeine, and alcohol use.
- Learn relaxation techniques such as guided imagery or meditation.
Developing a bedtime routine can help signal to your body that it’s time to slow down and get ready for sleep. Some tips for an effective routine include (MedLinePlus, n.d.):
- Only using your bed for sleeping and sex (that means no eating or watching television in bed!)
- Trying to wake up and go to bed around the same time every day
- Avoiding eating a heavy meal at least two hours before bedtime
- Doing a calming activity such as reading or taking a bath to prepare for bed
- Avoiding screen time before bed
- Making sure your bedroom is quiet, dark, and at a comfortable temperature
If you are still unable to fall asleep within 30 minutes, don’t stare at the ceiling. This will only make you feel frustrated and more awake. Move to another room and do a quiet activity until you feel sleepy again.
Sleep hygiene: what is it and 20 tips for better sleep
Talk to your provider
If you’ve made changes to your lifestyle and sleep habits without any improvement in your sleep, talk to your healthcare provider. There are medical conditions such as depression and pain or medications that can be interfering with your ability to get a good night’s rest. Your provider can help you uncover these and other obstacles to healthy sleep, then work with you to make a plan to manage your symptoms.
- Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. (2006). Sleep disorders and sleep deprivation: an unmet public health problem. Washington (DC): National Academies Press (US); 2006. 2, Sleep Physiology. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK19956/
- Karna B, Gupta V. (2021). Sleep disorder. [Updated 2021 Feb 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK560720/
- Li, J., Vitiello, M. V., & Gooneratne, N. S. (2018). Sleep in normal aging. Sleep Medicine Clinics, 13(1), 1–11. doi: 10.1016/j.jsmc.2017.09.001. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5841578/
- Patel AK, Reddy V, Araujo JF. (2021). Physiology, sleep stages. [Updated 2021 Apr 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK526132/
- Saletin J. M. (2020). Memory: necessary for deep sleep?. Current Biology: CB, 30(5), R234–R236. doi: 10.1016/j.cub.2020.01.038. Retrieved from https://pubmed.ncbi.nlm.nih.gov/32155430/
- U.S. National Library of Medicine. (2021). Healthy sleep. MedlinePlus. Retrieved from https://medlineplus.gov/healthysleep.html
- U.S. National Library of Medicine. (n.d.). Changing your sleep habits: MedlinePlus Medical Encyclopedia. MedlinePlus. Retrieved from https://medlineplus.gov/ency/patientinstructions/000757.html
- Zhang, Y., & Gruber, R. (2019). Can slow-wave sleep enhancement improve memory? A review of current approaches and cognitive outcomes. The Yale Journal of Biology and Medicine, 92(1), 63–80. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430170/