Deep sleep, also known as slow-wave sleep, is when your body restores and repairs itself. It's one of the most beneficial stages of sleep that helps you feel rested for the next day.

The main categories of sleep include REM (rapid eye movement sleep) and NREM (non-rapid eye movement sleep). Healthy people will cycle through these stages of sleep multiple times through the night before waking up.

However, no matter how hard we try, it's often difficult to get enough sleep. Experts state that we should be getting 7 - 9 hours of quality shuteye a night. But in reality, many people get 6 or less, with 1 in 3 American adults not getting enough sleep regularly.

If you fall into the insufficient sleep category, read on to learn more about deep sleep, the stages of sleep, the reasons you're not getting enough sleep, and tips to start getting more.

What Are the Sleep Stages?

During each night, you go through sleep cycles lasting from 70 to 120 minutes. Each person will experience four to six of these sleep cycles, depending on how much deep sleep is best for them.

A sleep cycle moves you through different stages of sleep including four non-rapid eye movement stages (75% - 80% of the night) and one rapid eye movement stage (20% - 25%). Here's a breakdown of sleep stages and what happens in each:

Stage 1

This stage only lasts a few minutes when you're drifting off. This is light sleep, when your heart rate and breathing begin to slow down.

Stage 2

Here, your heart rate and breathing slows even more. Your muscles start to relax and your temperature lowers. In the first cycle, you stay in this stage from 10 to 25 minutes, and as the cycles progress, this stage lasts longer. Overall, you'll spend 45% to 55% in this stage of sleep.

Stages 3 and 4

This part of the cycle is the deep sleep stage or slow wave sleep stage. You stay in stage 3 for a few minutes before transitioning into stage 4.

Here, your heart rate and breathing slow further, and the brain emits delta brain waves. These are associated with the deepest levels of healing, and restful sleep.

This deep sleep stage is thought to be where the best quality recovery of your body and mind takes place. Deep sleep is a hard place to wake someone up from and if you manage it, they will likely appear very groggy and disorientated.

The deep sleep stage lasts between 20 and 40 minutes in the first cycle. 10% to 15% of your total sleep time should be spent in this stage.

REM Sleep

In REM, your brain activity increases, temperature drops, and the eyes move around quickly under the eyelids. It's common to dream in this stage of sleep with 80% of vivid dream recalls happening here.

The REM stage of sleep only happens for 1 to 5 minutes in the first cycle and gets longer as the cycles progress. Muscles are mostly paralyzed during this stage, to stop you from acting out your dreams.

What is Deep Sleep?

Deep sleep, or slow wave sleep, happens in NREM sleep, in the third stage. Here, the brain's activity appears in long, slow delta waves at a frequency of 0.5 to 2 Hertz.

You typically fall into a deep sleep within the first hour and as the night wears on, the time spent in deep sleep decreases. During this stage, your muscles are very relaxed and your breathing and heart rate are slow.

Deep sleep is an important time when your brain rests and recovers, energy is replenished and your memory is reinforced. This is also an important stage for keeping hormones balanced, with the pituitary gland secreting a growth hormone to help the cells of the body regenerate.

Why is Deep Sleep So Important?

While the whole sleep cycle is important, getting quality deep sleep offers multiple mental and physical benefits. In this stage your immune system gets stronger, you secrete a growth hormone to help the body repair and the brain detoxifies.

This is also when your brain consolidates new information, and creates and organizes memories. Additionally, deep sleep is important for glucose metabolism and for replenishing energy stores.

If you don't get enough deep sleep regularly, this can start to impact your health. A lack of deep sleep can lead to:

Increased Pain

A reduced amount of deep sleep can make chronic pain worse. If you suffer from fibromyalgia, you may find that your symptoms become exaggerated.

Impaired Growth

Not being able to get a good night's sleep has been associated with growth problems for kids. A lack of deep sleep can interfere with growth hormones being released, which can lead to a slower rate of growth.

Lowered Immune Function

If you find it hard to fall asleep and drift into a deep sleep, this can lower your immune function, leading to frequent colds and common illnesses. You may also be at a higher risk for health problems such as heart disease, Alzheimer's, and a stroke.

Decreased Cognitive Function

Because deep sleep is where the brain rests and repairs, not getting enough can affect your ability to retain information and make it hard for you to focus.

How Much Deep Sleep Do You Need?

The recommended amount of total sleep an adult needs each night is 7 to 9 hours. However, each person is unique and will function well in different amounts.

Deep sleep should make up 10% to 15% of your total overall sleep. How much deep sleep you need will be self-regulated but will be affected by certain factors such as your age, how much sleep you had the previous night, if you have a sleep disorder or if you nap frequently during the day.

Try not to worry about how much time you're in this stage, as you can't control this. Instead, focus on how much overall sleep you're getting.

By aiming for the right amount of sleep each night, you give yourself a good chance of naturally cycling through the sleep stages and getting enough deep sleep.

It's also important to remember that as you age, you will need less deep sleep and spend more time in the stage 2 part of the sleep cycle.

What Causes a Lack of Deep Sleep?

Many factors can cause a lack of slow-wave sleep each night. Some factors are controllable, like reducing screen time in the evening and getting a better bedtime routine.

However, some factors are hard to control, such as working shifts and dealing with sleep disorders. Common factors that can reduce deep sleep hours include:

• Insomnia
• Jet lag
• Shift work
• Leg cramps
• Sleep apnea
• Circadian rhythm disorders
• Exploding head syndrome

Common Signs You May Not Be Getting Enough Deep Sleep

It can often be hard to pinpoint whether you're getting enough deep sleep or not. But, some indications you are lacking include:

• Finding it hard to focus and stay attentive
• Feeling drowsy and unrefreshed after waking
• Cravings for salt, sugar, and high-fat foods
• Trouble retaining information and forming memories

Tips to Increase Your Deep Sleep Time

Practicing good sleep hygiene is a recommended way to increase the number of hours you sleep. By establishing a good bedtime routine you'll improve sleep quality and get more hours of deep sleep. Follow these tips:

Create a Bedtime Routine

A relaxing bedtime routine helps your body wind down from the stresses of the day. It also signals to your brain that it's time to get ready for sleep. Aim for a 30 - 60 minute routine of consistent activities such as reading, listening to soothing music, and drinking chamomile tea.

Reduce Screentime in the Evenings

Put your electronic devices away at least one hour before bedtime. The blue light from screens can block melatonin, which makes us feel sleepy. If you must look at your phone, wear blue light-blocking glasses or dim the screen brightness.

Take a Warm Bath

Relaxing your body in a warm bubble bath one hour before bedtime can help to encourage slow-wave sleep. After heat is drawn to your hands and feet in the bath, this will dissipate, allowing you to cool and get to a favorable sleep temperature.

Try Yoga Poses for Sleep

Yoga is great for relaxation and can help to improve sleep quality. One study found that cyclic meditation - a form of yoga combined with rest periods - helped people to enjoy better quality sleep and deeper sleep.

Work Out Daily

Research has shown that those who exercise daily generally fall asleep faster than those who don't exercise at all. Aim for 150 minutes of brisk exercise a week, but don't exercise just before bedtime as this can keep you awake.

Increase Your Fiber Intake

A healthy diet can help you maintain a healthy weight and help you get a deeper sleep. One study showed that a higher fiber intake helped increase the amount of time spent in deep, slow-wave sleep.

Avoid Alcohol Before Bed

Alcohol might help you fall asleep, but it decreases the amount of time spent sleeping deeply. Because alcohol is a diuretic, it can also make you need to relieve your bladder in the middle of the night.

Avoid Caffeine Before Bed

Avoid caffeinated beverages at least 7 hours before bedtime. Caffeine is a stimulant and can make it harder for you to fall asleep. Stick to water, warm milk or chamomile tea, which are effective at inducing sleep.

Listen to White and Pink Noise

Soothing sounds are one way to help relax you at bedtime and encourage deep, peaceful sleep. White noise is useful for blocking out background noises if you live in a busy area.

Pink noise includes calming nature sounds such as rainfall, waves crashing, or the wind howling. This type of noise has been shown in studies to decrease the time it takes to fall asleep and enhance deep sleep.

Make Your Bedroom Sleep Friendly

Another way to encourage deeper sleep is to turn your bedroom into a sleep sanctuary. Eliminate bright lights and loud noises and make sure it's cool enough (between 60 and 67 degrees Fahrenheit).

Keep electronic devices out of the room and ensure you have a comfortable, supportive mattress. Change the light bulbs on your nightstand to warming amber, which will help create a relaxing ambiance.

Listen to Binaural Beats

A binaural beat is when you hear a different tone in each ear at slightly different frequencies. The difference between these frequencies is the binaural beat.

By listening to certain frequencies, your brain waves can be induced to match the beat frequencies. To encourage deeper sleep, listen to delta wave binaural beats, which may encourage the brain to produce delta waves like in stage 3 of the sleep cycle.

Who Struggles to Get Enough Deep Sleep?

Sleep deprivation is experienced by the majority of people occasionally. However, those with sleep disorders may find it hard to get the right amount of deep sleep on a regular basis.

If you have insomnia, your sleep schedule may vary, resulting in less deep sleep and more time in stage 1 of sleep. As you age, the amount of time spent in deep, slow-wave sleep, will also diminish.

Additionally, if you struggle with Alzheimer's or schizophrenia, you might experience less slow-wave sleep. Research has even shown that those living with a damaged hippocampus (brain memory center) often spend less time in the deeper sleep stage.

Is Light Sleep as Good as Deep Sleep?

While deep, slow-wave sleep is critical, light sleep has many benefits as well. For example, it pays to wake up naturally in this part of the sleep cycle, rather than jolting awake from the deep sleep stage.

There is no hard and fast rule for how much light sleep you need. Everyone's needs will vary. It's part of the falling asleep stage and is when the sleep cycle begins.

When to Talk to A Doctor About Sleep-Related Problems?

Restful sleep requires a healthy balance of the sleep stages. If you start to experience health problems due to a lack of sleep, such as a low mood, reduced cognitive function, or deterioration in your physical health, talk to your local GP.

If you can, start a sleep diary detailing your sleep habits and how you feel during the day. If symptoms persist, your doctor may suggest polysomnography or taking part in a sleep study. With this, you'll sleep in a lab while experts monitor your brain and body activity as you sleep.

Deep, slow-wave sleep is important, but try not to get fixated on this as you cannot control it. Instead, work on improving sleep hygiene which will add to your overall quality sleep time.

To help you along the way, use sleep aids such as the BetterSleep app. Here you can track your sleep and relax before bedtime with soothing tunes, guided meditations, and curated bedtime stories.