Slow-Wave Sleep: Why It’s Essential for a Good Night’s Sleep

by | Last updated Jan 12, 2023

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Slow-wave sleep is a crucial part of getting the rest you need each night, but do you know why it’s so important?

Sleep is a key biological function— everything in your body and your brain rely on adequate sleep to work properly. Slow-wave sleep helps to ensure that you get the deep, restful sleep you need to feel refreshed in the morning and ready to take on the day.

As you already know, there’s more to getting a good night’s sleep than just closing your eyes at night and waking up in the morning. So let’s take a look at what slow-wave sleep is, and the role it plays in getting a good night’s sleep.

What is Slow-Wave Sleep?

Slow-wave sleep (SWS), also known as N3 sleep or delta sleep, is the deepest phase of NREM sleep, or non-rapid eye movement sleep. It’s marked by high-amplitude, low-frequency brain waves. 

In the NREM phase, there is no eye movement, your breathing and heart rate slow, and your brain quiets down. Dreaming and conditions like sleepwalking can occur during this stage of brain activity. [1]

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Sleep Cycle Stages

Your sleep cycle each night is broken up into four stages:

  • Stage 1 (N1): Non-REM sleep that lasts between one and five minutes. Your muscles start to relax, and your heartbeat and breathing slow down.
  • Stage 2 (N2): Non-REM sleep that lasts between ten minutes and one hour. Your body temperature reduces, your heart rate and breathing slow further, and eye movement stops.
  • Stage 3 (N3): Non-REM sleep that lasts between twenty and forty minutes— slow-wave sleep occurs here. Your heart rate and breathing are at their slowest, and your body repairs itself and prepares for the next day.
  • Stage 4 (N4): Rapid eye movement (REM) sleep that lasts between ten minutes and one hour. Most dreaming happens here. Like the name suggests, your eyes move rapidly, and your brain activity, heart rate, and breathing all increase.

It’s important to get adequate N3 sleep each night— decreased slow-wave sleep contributes to light sleep, sleep disturbance during the night, and sleep deprivation.

Why Increasing Slow-Wave Sleep Is Essential for Good Sleep

You get your deepest sleep during N3 sleep, which means this stage is crucial to waking up feeling well-rested and like you got a good night’s sleep. 

The most important sleep stage for memory consolidation and overall sleep quality is slow-wave sleep (SWS). If you wake up feeling tired and sluggish, you likely had poor or disrupted slow-wave sleep.

Not only is stage 3 when you get your deepest sleep, but there are also numerous psychological and physical health benefits to getting adequate amounts of slow-wave sleep. 

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Some benefits of deep sleep include: 

  • A stronger immune system and enhanced immunity
  • Bone and tissue repair
  • Cell regeneration
  • Balanced blood sugar levels
  • Improved metabolism
  • Brain restoration and detoxification

Because your body uses slow-wave sleep to repair itself, a lack of SWS can be a major inhibitor for your overall health. 

Not getting enough SWS means you’re not getting enough deep rest. Without deep rest, you may begin to notice negative effects throughout your entire body, like short sleep duration, daytime sleepiness, and cognitive decline.

If you wake up during slow-wave sleep, you’ll probably feel disoriented, groggy, and sluggish. These interruptions to your sleep cycle harm your rest by disrupting this fine-tuned process. You need complete, uninterrupted sleep cycles to get a good night’s sleep.

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New Research: Naps Don’t Relieve Sleep Deprivation

A recent study from the Michigan State University Sleep and Learning Lab examined the role that short naps played in reducing the cognitive deficits associated with sleep deprivation. The research found that 30-60 minute naps did not show any measurable effects in counteracting the effects of sleep deprivation. 

Although participants getting slow-wave sleep during their naps helped reduce sleep deprivation-related impairments, it wasn’t enough to compensate for poor sleep the night before. [2]

After completing initial cognitive tasks the participants were separated into three groups: 

  • The first group was sent home to sleep
  • The second group stayed at the lab overnight and could take either a 30 or 60-minute nap
  • The third group did not sleep or nap at all

All participants completed more cognitive tasks the next morning. 

The group that took naps still experienced the ill effects of sleep deprivation and made significantly more errors than those who got normal sleep the previous night. However, increases in slow-wave sleep in the nap group reduced errors by around 4 percent for every 10 minutes of SWS. In total, they still performed worse than the participants who slept normally. 

While the idea of a short nap may sound like a restful solution to catch up on lost sleep, your body does not have an opportunity to fully recover from the lack of deep sleep you experienced the night before. 

This is why it’s so important to get a full night of quality sleep each night. Adequate slow-wave sleep is vital to morning alertness and wakefulness. SWS suppression contributes to cognitive impairment. This means memory and problem-solving difficulties, slower reaction time, and other problems are inevitable the next day (even when you try napping to make up for poor sleep). For example, you may show up to work in the morning asking the same questions repeatedly, or find that a simply tasks that normally takes an hour complete seems to take an entire afternoon. 

Get More “Deep” Slow-Wave Sleep by Sleeping Cooler

Your core body temperature is very important for getting the deep slow-wave sleep you need each night. Although slow-wave sleep is important for all ages, core body temperature seems to have a particularly pronounced effect on people who are older. 

It’s believed that individuals over 65 years old experience core body temperature drops during the midpoint of sleep. This means they reach their temperature minimum earlier than younger people, and the last half of the sleep period occurs as their body temperature is rising. 

This rising temperature curve has been associated with the decreased ability to maintain sleep. 

If you’re older, your maximum rate of temperature decline happens earlier. Therefore, how much sleep you get during the slow-wave sleep period— when your body’s core temperature is most likely to decline— is important for initiating and maintaining sleep. It’s also important for producing slow-wave sleep. 

However, older people’s sleep tends to occur later when it comes to this part of the temperature cycle. This produces subpar sleep continuity and less slow-wave sleep. 

Improve Slow-Wave Sleep By Increasing Core Body Temperature Before Bed

There are two ways to increase your amount of deep sleep each night: Allowing yourself enough total sleep time at night, and creating and supporting your ideal body temperature.

Slow-wave sleep is strongly correlated to whole-body cooling. Increasing your brain and body temperature before sleep (either with exercise or passive heating) results in heat loss during the night as your body cools itself down. That heat loss in turn increases the slow-wave sleep that you get.

One effective method is called passive body heating (PBH). Passive body heating increases the core body temperature followed by rapid cooling. Studies show that immersing yourself in 104 degrees Fahrenheit water for 30 minutes or more later in the day (ideally 60-90 minutes before bedtime) increases SWS regardless of age or fitness levels. 

In other words, a bath before bed can help your body get to the optimal internal temperature needed for a good night’s rest. 

Unlike vigorous exercise, passive body heating is an easy and ideal way for older people, who tend to get less SWS than their younger counterparts, to improve their sleep during this phase.

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How Can Sleep Apnea Affect Slow-Wave Sleep?

In addition to age and temperature, sleep apnea can negatively impact your deep sleep stage. 

If you have sleep apnea, you may experience airway collapse in deeper sleep states. If you have central sleep apnea, your brain will fail to properly signal respiratory muscles during sleep, while obstructive sleep apnea points to a physical blockage of your upper airway. [3]

Both of these forms of sleep apnea cause a reduction in slow-wave sleep and REM sleep. In fact, sleep the obstructive effects of sleep apnea on your way are most likely to occur in the deepest stages of sleep when you are most relaxed. 

The short-term effects of a lack of deep sleep caused by sleep apnea can lead to excessive daytime drowsiness, mental fog, and irregular sleep patterns. A prolonged lack of deep sleep caused by intermittent breathing from sleep apnea can lead to a number of long-term cognitive deficits. Strokes, depression, and even Alzheimer’s disease have been linked to the negative effects of sleep apnea. 

How Can Sleep Apnea Treatments Improve My Deep Sleep?

Detecting sleep apnea early is key. If you have Obstructive Sleep Apnea, you are going through multiple episodes of interrupted breathing, restricting the oxygen flow to your brain, every night. By reaching out to sleep experts to conduct a sleep study, doctors can properly diagnose your form of sleep apnea and offer treatment, usually in the form of a Continuous Positive Airway Pressure device (CPAP). 

CPAP has been proven to be the most effective sleep apnea treatment and has been shown to restore SWS and REM sleep in sleep apnea patients. [4]

Patients using CPAP therapy have experienced reduced respiratory events and restored sleep cycles. By treating the physiological effects of sleep apnea, slow-wave sleep increases. With this increase in slow-wave sleep, both short-term and long-term psychological repercussions of deep sleep deprivation decrease significantly. 

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When to Consult an Expert

Slow-wave sleep is vital to get the restorative sleep you need to be at your best each day. If you find that you’re consistently sleep-deprived and exhausted, then you may have a sleep disorder. Sleep disorders like insomnia or obstructive sleep apnea (OSA) can seriously impact the amount of deep sleep you get each night, and can even lead to health problems down the line.

If you think you may have a sleep disorder, it’s important to contact a sleep expert and get your symptoms evaluated as soon as possible.

A timely evaluation and appropriate treatment can be the difference between a good night’s sleep and another night of poor rest. Contact us at the Sleep Centers of Middle Tennessee today— we can help you get back to the deep and restful sleep you deserve.


1. Dijk, Derk-Jan. “Regulation and Functional Correlates of Slow Wave Sleep.” Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine, American Academy of Sleep Medicine, 15 Apr. 2009,

2. “Scrap the Nap: Study Shows Short Naps Don’t Relieve Sleep Deprivation.” ScienceDaily, ScienceDaily, 12 Aug. 2021, 

3. Marin-Oto, Marta, et al. “Long Term Management of Obstructive Sleep Apnea and Its Comorbidities – Multidisciplinary Respiratory Medicine.” BioMed Central, BioMed Central, 4 July 2019, 

4. Cheng, Jin-Xiang, et al. “Rapid Eye Movement Sleep and Slow Wave Sleep Rebounded and Related Factors during Positive Airway Pressure Therapy.” Nature News, Nature Publishing Group, 7 Apr. 2021, 

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