What Is Deep Sleep and How Much Do You Need?

Deep sleep^[1] means that a person is in a stage of rest in which it is hard to wake them because their brain waves are very slow during this time. The heart rate, breathing, and eye movements are at their slowest as well. This stage of sleep is important because it is the most restorative period, meaning it fosters physical growth, immune function, memory consolidation, and the hormones that control stress, appetite, and blood glucose levels^[1]. It has also been shown to be beneficial for managing stress, learning, preventing diabetes^[2] and obesity, physical energy, and strengthening your immune system.

In order to understand deep sleep, it’s important to know where it falls in relation to the other stages of sleep. There are two broad categories of sleep that we cycle through throughout the night: rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. NREM is further divided into three stages, N1, N2, and N3.

The body moves through each of these phases about four to six times per night, each of these sleep cycles lasting about 90 minutes. (So, one sleep cycle includes these four stages, totaling up to roughly 90 minutes per sleep cycle.)

Stage 1: The first stage of sleep is called N1^[2]. This non-REM stage is categorized as light sleep, and it is when you’re just drifting off. This stage only lasts about one to five minutes and includes a regular rate of breathing, sometimes a feeling as though you’re falling (perfectly normal), and if you were to get woken up during this stage, you might feel like you haven’t slept at all^[1].

Stage 2: The second stage of sleep is called N2. In this non-REM stage of sleep, eye movement stops, heart rate begins to slow down, body temperature drops, and brain waves begin to slow. This stage lasts about 25 minutes in the first cycle of the night and lengthens as you repeat the cycle throughout the night. Ultimately, you’ll spend about 45 percent of your total sleep in this sleep stage^[2].

Stage 3: The third stage of sleep is called N3. This stage of non-REM sleep is what we know of as deep sleep. During this stage, your brain produces delta waves, which are very slow brain waves. This is why deep sleep is also called “slow wave sleep.”

During this stage, you have no eye movement or muscle activity, and it is very hard to wake up during this stage [1]. If somebody does wake you up during deep sleep, you’ll probably feel groggy and disoriented^[3] for 30 minutes to an hour. This stage of deep sleep lasts about 20 to 40 minutes and makes up 25 percent of your total night’s sleep, and as we get older, less and less^[2].

This is the stage when our body repairs and regrows tissue, builds bone and muscle, and strengthens the immune system. It’s when night terrors, sleepwalking, and bedwetting occur^[2].

Stage 4: The final stage of sleep is rapid eye movement (REM) sleep. This stage usually starts about 90 minutes after falling asleep, and the first cycle of REM lasts only 10 minutes. These cycles will get longer throughout the night, though, with the final one before waking lasting up to an hour^[2].

It is during REM sleep that we experience faster breathing, rapid eye movements, increased brain activity, physical arousal, and vivid dreams^[1].

Research shows that about 25 percent of our sleep per night should be spent in deep sleep^[2]. That means if we spend eight hours sleeping, about two of those hours should be spent in deep sleep.

That being said, as we get older, we need less deep sleep, and we tend to spend less time there. This is a natural phenomenon and not something to be worried about.

In fact, a study titled Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem^[4] says that time in deep sleep declines by 2 percent every decade. This is because children and teens need more deep sleep than adults to support physical and cognitive growth. Young people experience abundant growth during this time and need the benefits of restorative sleep, whereas older people do not experience this same kind of physical and cognitive growth and therefore, need less of the sleep that facilitates it.

Deep sleep is valuable because it comes with multiple benefits to your cognitive, emotional, and physical well-being.

1. Lower stress levels: Deep sleep is beneficial for managing stress. Studies^[5] have shown that not sleeping enough can increase cortisol levels and increase anxiety. Further, deep sleep in particular has been found to “decrease anxiety overnight by reorganizing connections in the brain^[5].”
   

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2. Improved memory and learning skills: Getting adequate deep sleep is good for your memory and learning skills. Deep sleep^[6] fosters memory consolidation, which is crucial for learning and retaining new information. For this reason, deep sleep is important for people of all ages, including students and workers.
   

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3. Helps prevent diabetes and obesity: Deep sleep helps prevent diabetes and obesity^[7]. Two things can happen when you get good rest. First, the lack of sleep causes ghrelin hormone levels to increase, increasing your appetite. Second, too little rest can elevate blood glucose levels in the body. If this happens often, it may affect the body’s natural insulin resistance, resulting in diabetes.
   

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4. More physical energy: Deep sleep can increase your daytime energy^[8]. This sleep stage is highly restorative for the body, fostering tissue growth and repair. It allows the body to produce ATP, the body’s energy molecule, which will help us feel awake, alert, and clear the next day.
   

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5. Stronger immune system: Getting enough deep sleep helps maintain a strong immune system because this stage boosts immune function. The Mayo Clinic^[9] reports that important antibodies that fight off infections are reduced when sleep-deprived, leaving you more susceptible to illness.

Not getting enough sleep in general can be detrimental to your health, physically and mentally, and not getting enough deep sleep, in particular, has been found to have specific harmful effects.

1. Chronic pain: Studies^[10] show that a lack of deep sleep can cause a condition called fibromyalgia. This condition can cause chronic physical pain, depression, and fatigue [10]. Unfortunately, fibromyalgia also impacts the quality of sleep you’re getting, so deep sleep and fibromyalgia have a sort of cyclical relationship. Learn more: The Relationship Between Sleep and Pain
   

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2. Impaired growth in children: It is during deep sleep that children release the growth hormone. When kids experience less deep sleep, because of environmental factors or some sort of sleep disorder like sleep apnea, it can lead to a disruption in the release of this hormone. In other words, a lack of deep sleep^[11] can stunt your kids’ growth.
   

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3. Higher risk for Alzheimer’s or dementia: Research^[12] shows us that deep sleep is responsible for washing away toxic proteins. This process is known as the glymphatic system. When we don’t get enough deep sleep, this waste builds up in the brain, which is thought to be a leading cause of Alzheimer’s and dementia.
   

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4. Increases risk for chronic disease: Since deep sleep is an important part of maintaining a healthy immune system, it makes sense that a lack of deep sleep would mean a weakened immune system. This can lead to more minor illnesses like viruses and colds. It can also lead to more chronic illnesses^[13], such as diabetes, hypertension, and heart disease, as well as an increased risk for stroke, mood disorders, and cancer.
   

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5. Lower life expectancy: A chronic lack of deep sleep can result in a shorter life expectancy– which isn’t surprising, considering the impact it has on health in general. Research reveals that sleeping five hours or less per night increased people’s mortality risk by about 15 percent^[4].

Experts^[14] advise getting to sleep sometime between 8:00 p.m. and Midnight to get the best deep sleep. This is because you experience more non-REM/deep sleep in the earlier hours of the night, and you experience more REM sleep later in the night, as the outside shifts to morning light.

Regardless of when you go to bed, you’ll still shift from non-REM to REM sleep during certain times of the night. This means if you go to bed around 3:00 a.m., you’ll experience more REM sleep than deep, restorative sleep15.

This has to do with the way light outside regulates the body’s circadian rhythm, a series of physiological changes that follow a 24-hour cycle. One way it does this is by releasing more melatonin, a hormone that promotes sleep.

Melatonin amounts decrease throughout the night as the sun starts to come up. Additionally, trying to sleep when it’s light outside goes against the body’s natural rhythm, which is why many shift workers are prone to sleep deprivation. If your work schedule does not allow you to sleep on a consistent nighttime schedule, you should make your bedroom as dark as possible. Blackout curtains can help block out light that interferes with sleep.

If you’re concerned about the amount of deep sleep you’re getting, the good news is that are easy steps you can take to help get more of it.

1. Practice good sleep habits: Practicing good sleep hygiene should increase deep sleep. Good habits include cutting off electronics before bed, avoiding caffeine and alcohol, not eating big meals late at night, and managing stress.Devices like cell phones and computers emit a blue light that suppresses melatonin production, causing alertness. Caffeine can make it harder for you to feel tired at night, while alcohol^[15] has been shown to cause more fragmented sleep patterns. Eating too much food late at night can be uncomfortable, and certain foods may trigger heartburn. Not managing stress can affect your ability to relax and fall asleep.
   

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2. Consistent schedule: Keeping a consistent sleep schedule should improve your deep sleep because it helps set your internal clock. You need to establish a bedtime and wake-up that work for you and stick to those times every day of the week, including weekends.
   

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3. Comfortable bedroom and mattress: Ensuring your bedroom is comfortable will improve your rest. Experts say it’s best to sleep in a room that's cool. If your room does not meet these standards, you should find ways to improve it, such as using blackout curtains, earbuds, and opening a window. Additionally, the right mattress will help you sleep soundly. If you notice your bed isn’t as comfortable as you’d like, consider investing in a new mattress that’s a better fit for your needs and preferences.
   

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4. Treating sleep disorders and other health issues: Sleep disorders and other health issues can have a huge impact on your quality of sleep, so it’s important to treat those as soon as possible. Some sleep disorders may be managed through healthy lifestyle habits. If you continue to experience symptoms, speak with your doctor or a sleep specialist, who can help diagnose your condition and set up an appropriate treatment plan.

The primary distinction between deep sleep and REM sleep is that they are two different stages of sleep. Deep sleep is the third stage of the sleep cycle and the final stage of the non-REM phase. REM sleep is the fourth sleep cycle stage and the only stage in REM rest.

Deep sleep also exhibits the lowest brain activity, and REM sleep has the highest amount. Deep sleep is characterized by slow brain waves, heart rate, breathing, and eye movements. Conversely, REM sleep is characterized by quick eye movements and heightened brain activity^[1].

One of the similarities between these two stages is that it is harder to wake up in both deep sleep and REM sleep. Waking up during either of these stages can leave you feeling groggy and unrefreshed. Sleep experts recommend that people do not wake up during these stages in order to feel well-rested in the morning.

Read more about REM and NREM sleep stages.

The difference between deep sleep and light sleep is that it is harder to wake up during deep sleep than light sleep. Deep sleep is also the third stage of the sleep cycle, whereas the first two stages of the cycle are light sleep. You begin to doze off during light sleep, and your body and brain activity slow down until they reach their lowest point in deep sleep.

One similarity that deep and light sleep share is that they are both in the non-REM phase of the sleep cycle^[2]. As mentioned, sleep health experts say it’s better to wake up during light sleep because you're more likely to feel refreshed.

Yes, listening to music can help you get good deep sleep. Music and sleep quality are often connected because melodies and lullabies are popular for helping kids sleep better. Research suggests music may help adults sleep soundly too. A 2003 study titled The use of music to promote sleep in older women^[16] examined the effects of music on a group of women over the age of 70. They found that music decreased the time it took to fall asleep and the number of times they woke up during the night.

Reducing the number of times someone awakes overnight increases a person’s chance of getting more deep sleep, which means this news is helpful for older people since they experience a decline in deep sleep. The best music for sleep is slow and calming. A study titled Releasing stress through the power of music^[17] found that the ideal genres, instruments, and sounds include Native American, Celtic, Indian-stringed instruments, drums, flutes, nature, thunder, and rain.

Yes, meditation is good for deep sleep. Many people have difficulty sleeping soundly due to stress, and meditation provides a way to relieve stress. Meditation is a practice where an individual focuses on one particular thing, such as an image or object. The goal of meditation is to keep out thoughts that cause you to feel overwhelmed. It can be done any time of the day, but if you want to improve your sleep, schedule a time to meditate shortly before going to bed.

There are tips you can follow if you’re new to meditating. First, create a space to meditate that feels calming. Second, take some deep breaths as you try to focus and relax your mind. You can also try using a meditation app such as Headspace or Calm if you experience roadblocks.

Items you can use to get quality deep sleep include:

1. Eye Masks: Eye masks can help eliminate distracting light and are an economical alternative to blackout curtains. Many eye masks are available for 20 dollars or less. If you plan to use one, be sure that the fit and material are comfortable.
   

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2. Fans: Fans are a great way to sleep better because they keep you cool. If your room is too warm, this could cause you to awaken during the night. Keeping a fan on will help prevent you from overheating.
   

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3. Weighted blanket: Weighted blankets are a well-known method for improving sleep for those with anxiety. The weight of the blanket is designed to help provide emotional comfort for better rest.
   

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4. Essential oils: Essential oils are a great way to foster relaxation and better sleep. Many people choose to use a diffuser with essential oils to give their room a calming scent. One of the most popular scents for good sleep is lavender.
   

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5. CBD: CBD may help promote more deep sleep. CBD comes from marijuana, but it does not contain tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana that causes people to feel high. Studies^[18] have shown sleep improvements from using CBD. A common way to use CBD is through CBD oil, placing several drops under the tongue, and waiting 30-60 seconds before swallowing.

Yes, a mattress can affect deep sleep quality. A bed that doesn’t provide pressure relief, support, and other helpful features could lead to more restless nights. The right mattress should be a good match for your specific needs and preferences, such as your sleep position, how much you weigh, your health needs, and whether you sleep with a partner.

1. “Sleep Basics”. Cleveland Clinic. Last modified December 7, 2020. 
2. Patel, Aakash K., Reddy, Vamsi., Shumway, Karlie R., Araujo, John F. “Physiology, Sleep Stages”. National Library of Medicine. Last modified September 7, 2022. 
3. Hilditch, Cassie.J., McHill, Andrew W. “Sleep inertia: current insights”. National Library of Medicine. 2019.
4. Institute of Medicine (US) Committee on Sleep Medicine and Research. “Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem”. National Library of Medicine. 2006. 
5. University of California – Berkeley. “Stressed to the max? Deep sleep can rewire the anxious brain”.  Science Daily. 2019. 
6. “Sleep On It: How Snoozing Strengthens Memories”. National Institutes of Health. . 2013.
7. Farabi,  Sarah S. “Type 1 Diabetes and Sleep”. National Library of Medicine. 2016. 
8. “How sleep boosts your energy”. Harvard Health Publishing. 2020. 
9. Olson MD, Eric J. “Lack of sleep: Can it make you sick?”. Mayo Clinic. Last modified November 28, 2018. 
10. Choy, Ernest H.S. “The role of sleep in pain and fibromyalgia”. National Library of Medicine. 2015. 
11. “Can Lack of Sleep Stunt Your Growth?”. Nemours Teens Health. 2021.  
12. Michaud, Mark. “Not All Sleep is Equal When It Comes to Cleaning the Brain”. University of Rochester Medical Center. 2019.  
13. “Sleep and Disease Risk”. Harvard Medical School. Last modified December 18, 2007.
14. Heid, Markham. “What’s the Best Time to Sleep?”. Time Magazine. 2014.  
15. Thakkar, Mahesh M., Sharma, Rishi., Sahota, Pradeep. “Alcohol disrupts sleep homeostasis”. National Library of Medicine. 2015.  
16. Johnson, Julie E. “The use of music to promote sleep in older women”. National Library of Medicine. 2003. 
17. “Releasing stress through the power of music”. University of Nevada, Reno. Webpage accessed April 18, 2023. 
18. Shannon MD, Scott., Lewis ND, Nicole., Lee, Heather., Hughes PhD, Shannon. “Cannabidiol in Anxiety and Sleep: A Large Case Series”. National Library of Medicine. . 2019.