How Important Is Deep Sleep, Really?

Targeting deep sleep is all the rage but research shows you shouldn’t be playing favorites with your sleep stages. Here is the lowdown on deep sleep.

Man snoozing deeply in his bedroom
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Also known as “slow-wave sleep” or delta sleep, deep sleep is essential for feeling refreshed and present. But if you wake up frequently throughout the night — or consistently fall below 7-to-9 hours of nightly Zzz’s — you might not be getting enough of this restorative sleep stage.

“During deep sleep, your body slows down to recover, restore, and physically repair itself from the day. It’s your physically restorative sleep,” says Michael Breus, Ph.D., clinical psychologist and a fellow of The American Academy of Sleep Medicine. “When deep sleep is compromised, the overall quality of your sleep plummets.”

Getting more deep sleep might sound like a no-brainer; who doesn’t want to get better quality sleep and wake up in the morning feeling refreshed? However, there’s no secret code that lets you "hack” your sleep stages. That’s just not how sleep works. The best way to optimize deep sleep is to get enough sleep — with the help of proper sleep hygiene.

Keep reading to learn how deep sleep impacts the bigger sleep health picture.

Where deep sleep fits into the four sleep stages

At night, our body cycles through four sleep stages made up of rapid eye movement (REM) and non-REM sleep. Stages 1 through 3 are non-REM; stage 4, or REM sleep, is when most of our dreaming takes place.

The four sleep stages include:

  • Stage 1: The lightest sleep stage. This changeover from wakefulness to sleep typically lasts just a few minutes.  
  • Stage 2: The stage that takes us deeper into sleep as our heart rate and body temperature drop.  
  • Stage 3: Deep sleep. Our heart rate and body temperature become the slowest and lowest, and brain wave activity slows down even further. 
  • Stage 4: REM sleep. Our eyes move rapidly from side to side, our heart rate and blood pressure approach their wakening levels, and our brain activity increases significantly. 

“Deep sleep is referred to as delta sleep, or slow-wave sleep, because your brain activity, as measured by an EEG, consists of low frequency (1–4 Hz), high-amplitude fluctuations called delta waves, the characteristic slow waves for which this phase of sleep is named,” Breus says.

All four sleep stages are essential for your overall sleep health. However, deep sleep provides unique body benefits that can impact everything from heart health to immune function.

Benefits of deep sleep for your health

Why is deep sleep important to your health? As Breus puts it, “Deep sleep helps clean the system.”

During deep sleep, the pituitary gland secretes human growth hormone, which helps the body’s build-and-repair process and alleviates the effects of normal wear and tear. Increased blood flow to the muscles — a hallmark of deep sleep — helps encourage these repair functions.

Other health benefits of deep sleep include:

  • energy replenishment  
  • cellular regeneration  
  • memory processing 
  • immune system strength

While deep sleep helps your body recover, REM sleep provides mental and emotional restoration. REM sleep is primarily responsible for sorting through memories, but you need all four sleep stages to help with memory consolidation.

Light sleep vs. deep sleep: How long do these stages last? 

The four stages make up a sleep cycle, which averages about 90 minutes. When you’re getting enough hours of sleep, you’ll likely go through four to six sleep cycles per night.

Sleep stageChance of awakeningDuration
Stage 1 (NREM)High; it's the lightest sleep stage1 to 5 minutes
Stage 2 (NREM)Medium; brain activity helps avoid wake ups10 to 60 minutes, lengthening with each cycle
Stage 3 (NREM)Low; wake ups can cause grogginess20 to 40 minutes, with each cycle getting shorter
Stage 4 (NREM)Low; the brain responds to stimuli but most muscles are paralyzed 10 to 60 minutes, with each cycle getting longer

Deep sleep isn’t the longest sleep stage; that’s stage 2, which lengthens with each cycle and eventually makes up about 50% of total sleep. However, it’s the most difficult stage to wake from. If something startles you out of deep sleep, you’ll feel pretty groggy and disoriented — a phenomenon called “sleep inertia.”

What does enough deep sleep feel like? 

When you get enough deep sleep, you wake up feeling refreshed. When you don’t get enough, you’ll likely feel the opposite.

“If you wake up feeling unrested despite being in bed for 7 to 9 hours, and experience fatigue and fuzziness during the day, chances are your deep sleep is being short-changed,” Breus says.

Other clues that you’re not getting sufficient deep sleep include lacking enough energy to get through a typical day and feeling unfocused, unproductive, and not present.

Risks of not getting enough deep sleep  

Whether your deep-sleep deficit stems from sleep disruptions that cause awakenings or not enough hours of overall sleep, a deep-sleep deficiency can significantly impact your health. A lack of deep sleep increases your risk for heart disease and lowers immune function.

Research also suggests that too little deep sleep can lead to the accumulation of beta-amyloid plaques within the brain tissue. These plaques are a hallmark of memory impairment and Alzheimer’s disease. Sleep deprivation disrupts the brain’s cleansing process, which is thought to accelerate degeneration.

“Deep sleep may also have an important role in clearing metabolic waste from the brain through the lymphatic system,” Breus says.

How to get more deep sleep

Woman with a sleep mask on to get high quality sleep
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It’s not possible to control how long your body spends in each sleep stage. But here’s the good news: Your body, ever intuitive, is constantly adjusting your sleep cycle to make up for sleep loss. For example, if you have back-to-back nights of below-average total sleep time, on the second night you’ll get a disproportionately high amount of deep sleep to make up for what was lost the night before.

What does that mean for you? The best way to get more deep sleep is to get more sleep in general; your body will take care of the rest. But if you’re feeling out of sync with your body and need a few cues, here’s what Breus says can help.

1. Make time for more sleep 

“The most important thing that you can do to increase your amount of deep sleep is to allow yourself adequate total sleep time,” Breus says. 

If you need to wake up early or go to sleep later due to a project, make sure to adjust for the lost hours the next day. Sleep debt does accumulate, so you don’t want to put off your recovery sleep until the weekend. (Catching up on sleep that way also doesn’t work!)

2. Avoid alcohol, especially if you’re sleep deprived

Avoiding alcohol before bed is essential to any sleep hygiene checklist. Why? Because it affects the quality of your deep sleep. “When your body is busy processing alcohol, it has trouble getting past light sleep and into deep sleep,” Breus explains.

This is especially problematic because a large chunk of your deep sleep usually occurs during the first half of the night — the time most disrupted by a nightcap close to bedtime. 

3. Use a sleep tracker

Getting enough deep sleep means getting enough overall sleep. Not sure you’re getting the full 7 to 9 recommended hours? Try using a sleep tracker to monitor your sleep quality. The best sleep trackers will provide a full sleep cycle analysis, including a breakdown of your total sleep time, awakenings, and the time you spend in each of the sleep stages.

Not into sleep tracking? Try keeping a sleep diary where you note your fall asleep and wake-up times, plus any sleep disturbances you experience throughout the night.

4. Listen to deep-sleep meditations 

Research shows that meditation can help improve sleep quality for adults who suffer from sleep disturbances. If you find your mind filled with racing thoughts at night, meditation might be just the tool to get you out of your head and into sleep mode.

The meditation app Headspace has a section devoted to sleep, which includes meditations for sleep, sleep wind-downs, and sleep music — another sleep tool that Breus recommends.

5. Try relaxing music

Music has long been known to help soothe stressful, anxious thoughts. It can also help you fall asleep faster by triggering the release of sleep-friendly hormones, including serotonin and oxytocin, Breus says. If you want to incorporate music into your nightly routine, Breus recommends slow beats.

“The body and brain are highly responsive to music’s rhythm and tempo,” says Breus. “To move your body into relaxation and sleep mode, play songs that have a rhythm of about 60 to 80 beats per minute. Your heart rate will gradually adjust to match these slower beats, and your breathing will slow, putting you closer to a sleeping state.”

With good sleep hygiene comes good sleep (and more deep sleep)

There’s no way to control how long your body spends in each sleep stage. But there is a proven way to hack deep sleep: getting more sleep. And that starts with proper sleep hygiene. Through simple changes to your bedroom environment, lifestyle habits, and pre-bed routine, you can increase your likelihood of a great night’s sleep — and the restorative deep sleep your body craves.