What is deep sleep and why does it matter?

Deep sleep is the third stage in the sleep cycle, during which your body and brain function slows. It is critical for maintaining and improving overall health.

If you've ever woken up feeling groggy and unrested after what should have been a good night's sleep, it's possible the culprit was a lack of deep sleep. Later that day, you may have had trouble focusing on tasks and felt irritable. Most everyone has experienced this at some point.

Sleep quality is directly linked to your overall health and well-being. Accordingly, it's important to get enough deep sleep every night.

Here are the key details to know about deep, restful sleep as well as strategies for naturally improving your sleep quality.

What is deep sleep?

Deep sleep is the third stage in the sleep cycle, during which your body and brain function slows. It is followed by the final stage, rapid eye movement (REM), which often includes vivid dreams. Deep sleep is part of the non-REM (NREM) phase.

There are three stages of NREM sleep:

• Stage 1/N1: Lasting one to five minutes, this stage occurs when you first fall asleep and your body hasn't fully relaxed.
• Stage 2/N2: Once your body becomes more relaxed, your heart rate slows down. Brain activity also slows but still has short bursts of activity. This stage lasts 10 to 25 minutes.
• Stage 3/N3: This is the final NREM stage, when you enter deep sleep. Your body relaxes even more and you become difficult to wake up. Deep sleep lasts 20 to 40 minutes in early sleep cycles and gets shorter as you continue sleeping.

REM sleep occurs after deep sleep, usually 90 minutes after you fall asleep. Its conclusion marks the end of a sleep cycle (the average person completes four to six sleep cycles a night). During the first sleep cycle of the night, the REM stage lasts about 10 minutes. As the night goes on, each REM stage gets longer — ultimately lasting up to an hour.

Why is deep sleep important?

Every stage of sleep is necessary for your overall health, but deep sleep is especially critical. During deep sleep (also known as slow-wave sleep) your brain waves slow down. Your breathing and heart rate also slow down. All these physical changes result in several unseen benefits.

Organizes information you learned during the day

When you take in new information, your brain stores it for a short period of time, known as encoding. Deep sleep helps strengthen those memories so you can recall them later. If you're constantly sleep-deprived, your brain can't consolidate what it has learned.

Strengthens your immune system

Certain components of the immune system become more active when you sleep. For instance, your body produces more cytokines — proteins that act as messengers for the immune system — which are associated with inflammation. This helps you recover when you are sick or injured.

Repairs your body

Deep sleep releases growth hormones that build and repair bones, muscles and tissues. Inadequate sleep means your body isn't releasing enough growth hormones to support recovery and repair.

How to get deep, restful sleep

So how do you make sure you're getting enough deep sleep each night? These strategies can help create healthy sleep habits.

Minimize potential sleep disruptors

According to an American Academy of Sleep Medicine survey, light and noise are the most common sleep disruptors. Other typical sleep disruptors include:

• Health issues such as restless leg syndrome
• Ignoring tired cues before bedtime
• Lifestyle factors, such as excessive alcohol consumption
• Nighttime hunger
• Stress

Keep a regular sleep schedule

Your circadian rhythm — the body's internal 24-hour clock — works best when you go to sleep and wake up at the same time every day, including weekends. This helps your body learn when it's time to enter the deep sleep phase.

Maintain a dark, quiet sleeping area

Curtains or a sleep mask can reduce light disturbances. Ear plugs or a white noise machine can help drown out outside noise. Your room should also be a comfortable temperature. Aim for somewhere between 60 and 65 degrees Fahrenheit to avoid getting too hot or cold during the night.

Stop using screens before bedtime

Discontinue use of your phone or a television 30 to 60 minutes before bed. The blue light from screens tricks your brain into thinking it's still daytime, which makes it harder to fall asleep. As you head to bed, put your phone on silent mode to avoid notifications.

Improving deep sleep quality naturally

In addition to the measures outlined above, you can improve the quality of your deep sleep with a few lifestyle updates. Consider making the following changes to your daily life:

• Avoid drinking coffee or caffeinated beverages in the afternoon or evening.
• Do a calming routine — such as practicing deep breathing, performing stretching exercises or drinking a cup of herbal tea — to let your body know it's time for bed.
• Don't eat heavy meals or drink alcohol too close to bedtime.
• Get regular exercise, but not too close to bedtime.
• Spend time in natural sunlight to regulate your circadian rhythm.

Set yourself up for a successful night's sleep

So what is deep sleep good for? Physical and mental health for starters. It's also one of the best ways to strengthen your immune system and promote the release of growth hormones.

A few healthy habits like keeping a regular sleep schedule and getting enough physical activity can help ensure you sleep well. Prioritize getting a good night's rest and set yourself up for deep sleep. Your body and brain will thank you tomorrow.