While we all know that sleep is important, most people don’t realize that the type of sleep you get matters more than the overall number of hours you sleep. Modern research now indicates that “deep sleep” is not just essential for optimal health; you need deep sleep to stay alive.
Sleep is divided into different stages. REM (rapid eye movement) sleep is the stage where most of your dreaming happens. All other sleep is called non REM sleep, mostly because your eyes don’t move around. The deepest stage of non REM sleep (“deep sleep”) is so essential that long-term survival is impossible without it.
Individuals who inherit the rare disease called fatal familial insomnia are unable to get deep sleep. Over 18 months, the sufferer develops high blood pressure, memory and thinking dysfunction, sweating, and other symptoms that rapidly lead to death.
On a somewhat lesser scale, people at risk for Alzheimer’s disease also have an inexplicable lack of deep sleep. What happens during deep sleep that is so important to our health and survival?
New evidence suggests that this sleep stage is when the metabolic wastes accumulated during the day are “washed” out of the brain through the meningeal lymphatic system. This process, called the “brain waste removal system,” is activated only during deep sleep.
Now that you have a taste of the importance of deep sleep, let’s dive in and see how many hours of deep sleep you need each night. We’ll look at sleep cycles and see what they look like.
When you sleep, you don’t just lie down and go unconscious for 8 hours. You might close your eyes and feel yourself drifting off before falling asleep. While sleeping, you will have times when you dream and others when your body barely moves. These different types of sleep often cycle in specific patterns.
Sleep can be divided simply into REM and non REM sleep. This classification is easy to see with the naked eye when watching a sleeping person. If we instead use brain wave testing (electroencephalogram or EEG) during sleep, we can see that non REM sleep has its own divisions.
Non-REM sleep has three stages, called light sleep (N1), deeper sleep (N2), and deep sleep (N3). N3 sleep is also called slow-wave sleep (SWS) because the brain’s waves are very slow delta waves.
This is where the brain’s waste removal system is most active. Failure to get enough N3 (SWS) sleep means this essential process of waste removal is insufficient to support normal brain function.
The sleep cycle is the 90-minute pattern when we cycle from wakefulness into the various non-REM sleep stages, with REM sleep separating these deeper sleep stages.
In general, the first hours of sleep are when SWS is dominant. As the night wears on, the cycle persists, but more time is spent in lighter non-REM stages or REM stage sleep.
What do we know about deep sleep and how much we should get? Experts say that age can affect the number of hours of deep sleep you get. Older individuals have more difficulty getting enough hours of sleep and tend to awaken earlier than when they were younger.
While even healthy older adults often get fewer hours of deep sleep compared to young people, those with Parkinson’s disease and Alzheimer’s dementia have a striking absence of satisfactory deep sleep.
Just as some individuals do well on 6 hours of sleep nightly and others need much longer, there are variations in how much deep sleep you need per night. Your sleep patterns are genetically determined, so you can do little to counteract your individual sleep needs with any success.
Certain aspects of your lifestyle affect deep sleep. If you have sleep apnea, for example, you tend to sleep lighter and get fewer hours of deep sleep. Those with narcolepsy have reduced numbers of deep sleep hours.
After a traumatic brain injury, the number of total sleep hours is reduced; part of daytime dysfunction in these people comes from too little deep sleep. Finally, alcohol might give you the perception of sound sleep, yet it adversely affects the number of deep sleep hours you get.
The National Sleep Foundation has weighed in on how much deep sleep you need. Remember that your needs vary with age. A healthy adult needs about 7 to 9 hours of sleep nightly.
If you get this much sleep, about 10 to 20 percent of it should involve N3 deep sleep. This means you’re normal if you get 70 to 180 minutes of deep sleep per night.
Age matters in how much overall sleep you need. A newborn can get as much as 18 hours of sleep per day but rarely knows the difference between night and day. By the age of 1 year, only 11 to 14 hours of total daily sleep are needed.
The number of recommended hours of sleep gradually diminishes so that healthy teens get 8 to 10 hours of sleep. Adults need about 7 to 9 hours of sleep. Older adults need the same number of total sleep hours; however, they rarely get this, even when healthy.
You can determine your own sleep needs by studying the number of hours of sleep you get each night and comparing how well-rested you feel the next day.
Many smartwatches track total sleep hours and can tell you how many hours of deep sleep you get each night. Such watches are moderately accurate in helping you see what your own sleep needs might be.
Deep sleep is more essential to health than REM sleep, possibly because of its crucial function in helping remove metabolic wastes from the brain. There are several known complications of getting too little deep sleep:
- Dementia – We know that those with Alzheimer’s disease have too little deep sleep. Experts surmise that getting too little deep sleep may also contribute to dementia.
- Poor immune system – Deep sleep enhances your immune function. If you get too little deep sleep, you risk infections from bacteria and viruses.
- Stroke and erectile dysfunction – both of these disorders are due to vascular dysfunction, which can arise when you get too little deep sleep.
Sleep deprivation has both long and short-term ill effects on your mind and body. No one has survived longer than 11 days without sleep. Those who have tried sleep deprivation as a challenge or prank have psychosis, severe memory issues, and cognitive distortions.
Children without adequate sleep suffer from behavioral issues and poor learning, while adults without sleep have dysfunction of blood pressure, weight, metabolism, and immune system activity. Emotions, thinking, and memory are adversely affected by lack of sleep.
It is entirely possible to increase the number of minutes of deep sleep you’re getting. Sleep hygiene practices can make sure you fall asleep more quickly and remain asleep. Here are some important sleep-enhancing tips:
- Get longer stretches of sleep to ensure you go through as many 90-minute cycles as possible during the night.
- To remain sleeping, make sure your sleep environment supports proper sleep. Avoid screens (laptops, tablets, and phones) before bedtime. Keep your sleep environment cool, dark, and quiet.
- Consider napping. Napping would normally be discouraged, yet you tend to get a higher proportion of deep sleep during shorter stretches seen when napping. If you have a short night of poor sleep quality, try napping the next day for up to an hour.
- Avoid sleeping pills and alcohol before bed. These substances impair your ability to get deep sleep, even if you sleep for the same number of hours as you normally would.
- Try to go to bed and awaken at the same time of the day, regardless of whether you are working or relaxing that day.
Your body responds best to consistency and natural methods of getting to bed. Once you establish a sleep schedule that works for you, periodically reassess to make sure you feel healthy and well-rested.
While not everyone needs nightly tracking of their sleep, you may need to do this if you know you have sleep issues or struggle with getting enough deep sleep.
Sleep tracking options are available on nearly every smartwatch, including Apple, Garmin, Fitbit, and other Android-capable watches. The choice you make generally does not matter as long as the watch measures the different sleep stages. Most watches come with free apps if all you need are the basics.
Oura rings will also track your sleep stages with its own app. There are a few under-the-mattress devices that track sleep without requiring a wearable. No two devices are the same, but if you use the same one consistently, you will get enough good data on your deep and total sleep times.
A sleep diary is essential to fixing your need for more deep sleep. In your diary, put your diet, stress levels, alcohol intake, and stress levels. You can also add other information that makes sense for you, including things like air quality and sicknesses.
Once you combine this information with how well you slept the night afterward. This is invaluable in helping you learn what parts of your life impact sleep the most.
If you find that your sleep is not improving or if you are concerned by what you see while sleep tracking, be sure to seek professional advice. A professional trained in sleep disorders can help you determine what’s going on and how to fix it to achieve better sleep.
Sleep is just as essential to life as breathing, eating, and drinking fluids. Deep sleep is particularly important for brain health because of its role in flushing metabolic wastes from the central nervous system.
Without this functional ability, you risk cognitive decline, mood swings, and whole-body metabolic dysfunction. Diseases like Parkinson’s disease and Alzheimer’s dementia are highly tied to a lack of deep sleep.
Your own sleep needs will vary with age and lifestyle. You need to pay close attention to the number of hours of total and deep sleep you get each night and correlate these numbers with how you feel the next day and over time.
While you may function well on fewer hours of sleep than most people you know, researchers are quick to point out that prioritizing restful sleep is important at any age.
Your health and well-being will improve greatly once you establish regular quality sleep and get enough deep sleep during the night.