Sleep is the foundation of a happy and healthy life. Sleep not only restores youth, vitality, strength, and health but also sharpens the mind, improves our memory, and enhances our emotional intelligence. Sleep can even help us recover from emotional trauma.
But did you know that not all sleep is equal? When we sleep, we actually experience many different types of sleep called sleep stages. Each sleep stage serves different functions and provides unique benefits for the mind and body.
In this article, you’ll learn all about the sleep stage known as deep sleep or slow wave sleep. First, you’ll learn about the biology of deep sleep – what is happening in the brain and body during this sleep stage. You’ll also learn about some of the most important benefits of deep sleep, including the benefits of deep sleep for physical restoration and memory. Finally, you’ll learn how much deep sleep we need along with some tips and strategies to experience more deep sleep.
What is deep sleep?
Deep sleep (also known as slow wave sleep) is the deepest phase of Non-REM sleep and is characterized by delta waves on an electroencephalogram (EEG). Delta waves are slower and less frequent than other types of brain waves that characterize other states of sleep and wakefulness https://www.sciencedirect.com/topics/neuroscience/alpha-wave#:~:text=Alpha%20waves%20are%20seen%20in,transition%20from%20wakefulness%20to%20sleep.:
- Alpha waves are present during a normal wakeful, but relaxed state.
- Beta waves are present when we are alert/attentive and thinking actively.
- Theta waves are present during the transition from wakefulness to sleep.
Compare delta waves to other brain waves with the chart below:
Deep sleep is also characterized by difficulty waking. During deep sleep, we become almost completely unresponsive to external stimuli. In addition, slow heart rate, blood pressure, and breathing also lead to a feeling of grogginess upon waking from deep sleep.
What happens to the brain and body during deep sleep?
Although delta waves and difficulty waking are the primary characteristic of deep sleep, they aren’t the only features of deep sleep. The body and brain experience many changes during deep sleep, each of which serves a specific purpose and provides us with a specific benefit.
1. Sympathetic nervous system (SNS) activity decreases
The sympathetic nervous system (SNS) is responsible for the body’s fight-or-flight response (our rapid involuntary response to dangerous or stressful situations). Thus, the SNS plays a major role in regulating body temperature, breathing rate, hormone flow, and blood pressure.
During deep sleep, the brain communicates a calming signal to the fight-or-flight branch of the sympathetic nervous system ((https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3018785/)), causing our breathing and heart rate to slow down significantly. In fact, our heart beats about 20% to 30% slower during deep sleep than it does when we’re awake. This reduction in blood pressure at night is crucial for experiencing healthy blood pressure the following day and maintaining healthy blood pressure in general. https://www.ahajournals.org/doi/full/10.1161/01.hyp.27.6.1318 Likewise, healthy blood pressure is important for maintaining heart health and reducing risk of heart disease.
2. Parasympathetic nervous system (PSNS) activity increases
The parasympathetic nervous system (PSNS) is responsible for stimulation of “rest-and-digest” or “feed and breed” activities, including digestion and sexual arousal. In other words, the PSNS helps regulate both digestion and sex drive. The PSNS also plays a major role in slowing heart rate.
The PSNS can be thought of as producing the opposite effect of the SNS. While the SNS causes a state of stress (useful during dangerous situations), the PSNS causes a state of relaxation, ultimately assisting many bodily functions.
During deep sleep, the PSNS is more active. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3018785/ That means, deep sleep likely plays a major role in regulating many bodily functions, including digestive health, reproductive health, and heart health.
3. Secretion of human growth hormone (HGH)
- Restoring bones and tissues, which promotes physical well-being
- Regulating blood glucose levels, which reduces risk of diabetes
- Stimulating the immune system, which helps with sickness prevention and recovery
The pituitary gland secretes HGH throughout the day and night. That being said, nearly 50% of all HGH secretion occurs during deep sleep. https://en.wikipedia.org/wiki/Growth_hormone That means, deep sleep plays a major role in promoting physical well-being, reducing diabetes risk, preventing sickness, and helping the body recover from sickness.
4. Glymphatic system activity increases
The glymphatic system is responsible for getting rid of waste buildup in the brain, including amyloid and tau proteins, which have been linked to Alzheimer’s Disease. https://www.semanticscholar.org/paper/Age-dependent-suppression-of-nocturnal-growth-sleep-Mullington-Hermann/fbf9661c7a6a041202d67d1d550f7d1b708250fc
The glymphatic system is another system that’s more effective during deep sleep than it is during other stages of sleep and wakefulness. https://www.medicalnewstoday.com/articles/324425
In a recent study, scientists have discovered that glial cells of the glymphatic system shrink in size by up to 60 percent during deep sleep. They concluded that this shrinking enlarges the space around neurons so that cerebrospinal fluid can proficiently clean out metabolic waste, like the waste proteins that cause Alzheimer’s Disease. https://www.sciencedaily.com/releases/2019/02/190227173111.htm
5. Brain activity during deep sleep
Scientists have long associated deep sleep with memory consolidation (the transfer of memories from short-term to long-term storage). Many studies demonstrate that the more deep sleep we get, the more information we remember the following day. https://www.nih.gov/news-events/nih-research-matters/how-sleep-clears-brain Other studies demonstrate that deep sleep also plays a part in spatial memory. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768102/ That being said, scientists are still trying to figure out how.
In a 2016 study, scientists at the University of California Riverside used a computational model to explore the role of slow wave sleep in memory consolidation. Based on their findings, they determined that, during slow wave sleep, sharp ripples in the hippocampus (responsible for short-term memory) influence synaptic changes in the cortex (responsible for long-term memory), ultimately leading to memory consolidation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768102/
How much deep sleep do we need?
At this point, you might be wondering how much deep sleep we need in order to reap all of the benefits mentioned above. That short answer is: not much. The average healthy adult only gets about 1 to 2 hours of deep sleep per 8 hours of nightly sleep. That’s about 13 to 23% of total sleep time. https://www.sciencedaily.com/releases/2016/04/160414214830.htm
That being said, in order to achieve this 1 to 2 hours nightly, you should be sleeping for between 7 and 9 hours each night. Fortunately, if deep sleep is cut short one night, from sleeping for less than 7 hours, the body and brain will compensate with more deep sleep the following night. Unfortunately, however, if short sleep duration is a regular occurrence, the body will grow accustomed to short deep sleep duration as well and will no longer compensate for loss of deep sleep. The result will be sleep deprivation and the consequences that come with it.
It’s also important to note that many people need more deep sleep than average. This is usually achieved by simply extending total sleep time. People falling into this category include growing children and adolescents, athletes, and people who are fighting off an illness.
Lastly, although normal healthy adults experience deep sleep for between 13 and 23% of their total sleep time, not everyone is so lucky. Some people, especially people who have trouble sleeping in general, have trouble experiencing deep sleep. Instead, they find themselves tossing and turning all night long, transitioning between states of light sleep, REM sleep, and wakefulness.
Fortunately, there are a number of strategies that have shown some promise in terms of increasing deep sleep.
Tips and strategies to improve deep sleep
As mentioned, the best way to get more deep sleep is to improve your total sleep duration. Doing so allows the body to go through more sleep cycles, which makes it possible to have more deep sleep.
If you’ve improved your sleep duration, but still think you need more deep sleep, here are a few tips:
- Engage in intensive physical activity. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385214 (Just make sure you do so at least an hour before bedtime so your body has time to decrease its temperature and heart rate before bed.)
- Cool down your body temperature by taking a hot bath or shower 1 to 2 hours before bed. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385214
- Listen to pink noise (slightly different that white noise) while falling asleep and throughout the night. https://www.frontiersin.org/articles/10.3389/fnhum.2017.00109/full
- Avoid caffeine later in the day. Caffeine greatly disrupts deep sleep. https://www.frontiersin.org/articles/10.3389/fnhum.2017.00109/full Try a caffeine-free herbal infusion instead.
- Make dietary changes that include fewer carbohydrates and more fats. https://ascpt.onlinelibrary.wiley.com/doi/abs/10.1002/cpt1976206682
Tips to improve sleep in general
- No caffeine after 3:00 PM. Recommendation: Switch to a caffeine free herbal infusion
- No long naps in the afternoon. Recommendation: Cut the naps down to 20 minutes.
- No blue light at least an hour before bedtime. Recommendation: If you can’t avoid the screens, try some glasses that block blue light.
- No light in your bedroom. Recommendation: Try a sleep mask or blackout curtains
- No noise in your bedroom. Recommendation: Use earplugs, headphones (designed for sleeping), or a white noise machine to block out the distracting noise
- If you’re travelling and suffering from jet lag, try taking a melatonin supplement to regulate your circadian rhythm.
If you’re too anxious or nervous to sleep, try natural sleep supplements, herbal infusions, or essential oils to help you relax.
Sleep is the foundation of a happy and healthy life with many benefits for the mind and body.
Deep sleep is one of the most important sleep stages for physical restoration, general health, and memory consolidation.
The best way to improve your deep sleep is to improve your sleep in general, but there are many tips and strategies you can use to target and improve your deep sleep.