You may have read countless articles that recommend getting between 7 and 9 hours of sleep every day. However, many of these publications don’t emphasize that when it comes to sleep, quality matters just as much as duration.
There are various ways to gauge sleep quality. For instance, you’re considered to have had a restful sleep if you can sleep for longer hour blocks uninterrupted.
Another critical aspect of quality sleep relates to the duration spent in the various sleep phases.
This article examines the third sleep phase, called deep sleep, focusing on how it might impact your health and lifestyle.
What Is Deep Sleep?
The best way to define deep sleep is to start by understanding the various phases of sleep.
In a typical sleep cycle, the body undergoes two main sleep phases. They include non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep.
Rapid eye movement, as the name rightly implies, is a sleep phase marked by quick, involuntary movements of the eyeballs within the sockets. Other key occurrences during REM sleep include elevated brain activity (causing intense dreaming) and ataxia (temporary loss of muscle activity).
Non-rapid eye movement is the opposite of REM. This sleep phase typically doesn’t involve eye movements. It’s also marked by less intense brain activity compared to REM sleep.
There are three distinct stages of non-rapid eye movement sleep: NREM Stage-1, NREM Stage-2, and NREM Stage-3. NREM Stage 3 is what constitutes deep sleep.
Note that we experience all three phases of NREM sleep in the given sequence before transitioning into REM sleep.
What Happens During Deep Sleep?
Deep sleep, known as NREM Stage 3, is the final phase of non-rapid eye movement sleep. It comes right before transitioning into REM sleep.
Deep sleep sets in about 20–40 minutes after falling asleep. The duration spent in this phase varies throughout the sleep cycle. Healthy individuals will have more hours of NREM Stage-3 sleep during the initial stages of their sleep cycle. The time then shortens gradually as you approach dawn.
True to its name, a person in deep sleep is deep asleep. Therefore, they’re challenging to awaken. If you happen to be awakened while in NREM Stage 3 sleep, you’ll likely battle grogginess throughout the day.
Grogginess is a feeling of fatigue and confusion experienced during the day. Many people attribute the condition to sleep deprivation in general. However, grogginess mostly results from having inadequate deep sleep.
Another thing that happens during deep sleep is that the body slows down. Cardiovascular and respiratory activities tend to be at their lowest during NREM Stage 3 sleep. That means a slow heart rate, breathing and reduced body temperature.
As already hinted, brain activity also slows down during deep sleep.
NREM Stage-3 is marked by a slowdown of the brain’s electrical activities into long, slow waves called delta waves. That explains why this sleep phase is alternatively known as “slow-wave sleep.”
What Are the Health Benefits of Deep Sleep?
1. Deep Sleep May Speed Up Muscle Recovery
Muscles are generally more relaxed in deep sleep than in NREM Stages 1 and 2.
Muscle relaxation reduces the risks of spasticity, thereby enhancing blood circulation. It’s important to keep your blood flow in check during deep sleep, considering that your heartbeat slows down significantly.
Muscle relaxation during sleep also means you’re unlikely to be awakened by muscle cramps. Most importantly, it can speed up recovery from muscle pains and inflammation.
2. Deep Sleep May Improve Cognitive Performance
We’ve already mentioned the delta waves that characterize deep sleep. Numerous studies have shown that delta waves may improve cognitive performance.
Getting adequate deep sleep may enhance various aspects of brain performance. These include thinking abilities, problem-solving skills and attention span.
So, if you know of a child suffering from cognitive issues like attention deficit hyperactivity disorder (ADHD), you might recommend restful sleep before exploring other interventions.
3. Deep Sleep May Promote Retentive Memory
Staying with cognitive performance and getting sufficient deep sleep may also boost your memory.
In fact, NREM Stage-3 is so deeply involved in memory consolidation that this sleep phase has earned the name “sleep-dependent memory processing.”
Studies have particularly cited deep sleep for its ability to aid spatial declarative memory, a phenomenon in which short-term memories get consolidated into long-term ones through repetition.
4. Deep Sleep May Escalate Wound Healing
Not only is NREM Stage-3 sleep effective at inhibiting muscle spasticity during sleep, spending more hours in this sleep phase may also promote wound healing in the muscles, skin, bones, and other tissues.
Note that most of the body’s restorative processes occur during deep sleep. During this stage, you’ll recover from microscopic tissue damages incurred while engaging in strenuous activities.
5. Deep Sleep May Aid Growth and Development
During deep sleep, the pituitary glands in the brain release growth hormones.
As the name suggests, growth hormones are responsible for various growth aspects. They’re primarily involved in increasing height.
Elevated endocrine activities during deep sleep may also prevent unhealthy weight gain. For instance, insulin secretion typically increases during NREM Stage-3. More insulin in your bloodstream can prevent the dangerous accumulation of glucose, averting complications like weight gain. Additionally, if you’re wondering how to regain a sense of smell, it’s important to consider factors like sleep quality and overall health, as they can play a role in sensory perception.
The Bottom Line
Deep sleep plays a crucial role in aiding growth and development. This sleep phase may also provide several therapeutic benefits. Therefore, ensure you get the recommended daily sleep intake every night (or every day, depending on your work shift).
