Deep sleep describes a particular stage of sleep that is important for waking up feeling refreshed and alert. Although there are no definitive guidelines for how much deep sleep you need, experts say that most adults need between seven and nine hours of sleep each night.
There are two types of sleep: rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. There are three stages of NREM sleep: stage 1, stage 2, and stage 3. Deep sleep is a term that describes stage 3 of NREM sleep. Each sleep stage is associated with certain physical processes and benefits, and people cycle through each of these stages several times during a night of sleep.
Learning more about the function and importance of deep sleep can help you get the most out of your nightly rest. We consider the benefits of this sleep stage, the risks associated with a lack of deep sleep, and tips for improving your sleep hygiene.
What Is Deep Sleep?
Deep sleep refers to stage 3 of non-rapid eye movement sleep. During this sleep stage, a person’s heart rate, blood pressure, and breathing slow until they reach their lowest levels of the night. Stage 3 sleep is a period of deep muscle relaxation and is often perceived by sleepers as the most refreshing and high quality portion of sleep.
Deep sleep is also called slow-wave or delta sleep, due to the characteristic brain waves that occur during this stage. Sleepers are often hardest to wake up during stage 3 sleep and, if awakened, may experience a period of mental fogginess called sleep inertia.
Initial periods of deep sleep last around 20 to 40 minutes at a time. Periods of deep sleep are usually longer early in the night, likely because a person’s need for rest is highest just after falling asleep. Until middle age, people spend about 10% to 20% of their total sleep time in deep sleep. The percentage of time spent in deep sleep decreases as a person gets older.
The Importance of Deep Sleep
Although scientists are still learning about the purpose and benefits of sleep, it’s clear that sleep impacts just about everything in the mind and body, from mood and immunity to overall health. Deep sleep in particular appears to provide a number of important health benefits.
- Promotes feeling rested: Deep sleep is necessary to waking up feeling refreshed and renewed. This benefit may be related to deep sleep’s role in relieving the pressure to fall asleep, which builds during each waking hour.
- Supports memory consolidation: Researchers believe that during deep sleep the brain recalls new information learned during waking hours and transfers it to long-term memory.
- Heals damaged tissue: Deep sleep promotes the release of human growth hormone, which may support the development of muscle and other tissues in the body. Human growth hormone may also help the body regenerate cells and heal damaged tissue.
- Fortifies the immune system: Hormonal changes during deep sleep enhance the immune system. In particular, these hormonal changes support the body’s ability to develop acquired immunity, remembering and better defending against specific pathogens.
What Happens if You Don't Get Enough Deep Sleep?
Although it can be challenging for researchers to differentiate the effects of losing deep sleep from sleep deprivation in general, studies have found several potential consequences of insufficient deep sleep.
- Sleep inertia: Sleep inertia describes the feeling of grogginess, disorientation, or a reduction in performance that can occur after waking up. People who wake up during deep sleep may experience sleep inertia for 30 to 60 minutes.
- Impared memory: Deep sleep plays an important role in forming long-term memories. Insufficient deep sleep may lead to forgetfulness and poor retention of memories.
- Risk of diabetes: Insufficient deep sleep may increase the risk of diabetes through reducing insulin sensitivity, which describes how well cells are at absorbing blood sugar.
- Hypertension: Blood pressure reaches its lowest point of the day during deep sleep. Losing deep sleep may increase the risk of high blood pressure, a medical condition called hypertension.
- Mood changes: Early research suggests that a reduction in deep sleep may make it harder to maintain a positive mood during the day.
Reduced deep sleep can also contribute to poor overall sleep quality, which in turn can lead to additional symptoms of sleep deprivation, such as:
- Difficulty focusing and staying alert
- Irritability, frequent bad moods, and low energy
- Slowed reaction times
- Memory issues
- Chronic medical conditions, including heart disease, obesity, and depression
- Other issues at work, school, or in social settings
Signs You May Not Be Getting Enough Deep Sleep
Because deep sleep is closely tied to a person’s sleep drive, daytime sleepiness may be a sign of insufficient deep sleep. Daytime sleepiness may cause a person to drift off while riding in the car, watching TV, reading, or after meals.
Other effects of not getting enough deep sleep may mirror those seen in people with sleep deprivation. Everyone responds to a lack of sleep differently, but common signs of sleep deprivation include:
- Difficulty focusing and paying attention
- Trouble learning new things
- Poor decision-making
- Emotional problems
- Difficulty remembering information
Tips for Getting More Deep Sleep
Although there are no guidelines for increasing deep sleep, taking steps to improve your sleep hygiene may improve sleep quality and support adequate deep sleep. Sleep hygiene is a term used to describe healthy habits that may help you get better rest.
- Exercise regularly: Exercise has been shown to help people fall asleep faster and stay asleep. Working out might also increase the amount of time spent in deep sleep and improve the quality of deep sleep. Try to get at least 30 minutes of exercise a day, preferably more than three hours before bedtime.
- Avoid caffeine and alcohol before bed: Alcohol and caffeine should be avoided close to bedtime, as they may reduce the amount of time spent in deep sleep.
- Get sunlight exposure during the day: Exposure to light is important for maintaining healthy sleep patterns. Wake up with natural sunlight and lower the lights indoors before bedtime.
- Maintain a consistent sleep schedule: Going to bed and getting up at the same time, even on weekends, may help you sleep better. Avoid staying up too late, or trying to catch up on lost sleep by sleeping in.