Tell me if this sounds familiar: You go to bed intending to sleep at least
seven hours so that you’re ready to start the next day bright and
early. When your alarm goes off, you think, “Great, I got
so much sleep,” only to find yourself yawning non-stop and fending
off the urge to lie back down.
Well, optimum sleep is more than just the number of hours you get each
night. It’s also a bit of a complicated puzzle involving sleep cycles
and stages, each with its own purposes and benefits. And if you’re
trying to boost the quality of your shut-eye, looking at your deep sleep
can be particularly beneficial to understand how it all fits together.
What Is Deep Sleep?
In short, deep sleep is an important stage in the sleep cycle, and it’s
key for keeping your mind and body in tip-top shape. But what does that
While you might be ready to check out when your head hits the pillow, the
work is just beginning for your body and brain. From the time you declare
lights out to hitting snooze on your alarm, your body will likely go through
four to five (and sometimes six) sleep cycles, with each cycle lasting
about 90 to 120 minutes, according to the
Experts believe each sleep cycle has two phases: non-rapid eye movement
(NREM), which has three stages, and rapid eye movement (REM), which has
one stage, according to the
National Institutes of Health (NIH).
When you go to sleep, you’ll typically start at NREM stage 1, then
move between NREM stages 2 and 3, and then cap off the process with REM
sleep before starting a new cycle, per the Cleveland Clinic. That said,
not everyone will move through this cycle in chronological order, and
some people may skip a stage or two, according to the
Mayo Clinic. That’s what makes
sleep so individual.
Deep sleep (NREM stage 3), which is what we’re focused on here, is
also called slow-wave sleep because of the characteristically
slower delta brain waves. You’ll typically spend more time in this restorative sleep stage
earlier in the night, per the NIH.
During deep sleep, your heart and respiratory rates are slow and your muscles
are relaxed, allowing you to benefit from restorative snoozing that’s
necessary for overall health (more on that below). This state of deep
relaxation is also why it’s difficult to wake someone up during
Why Is Deep Sleep Important?
So, what exactly is so important about deep sleep? During NREM 3, the body
undergoes significant physical repair and restoration, including muscle
recovery, tissue growth, and the release of growth hormones. It’s
also the stage where your brain processes and consolidates information
and experiences from the day, helping you retain and make sense of new things.
What’s more, getting sufficient deep sleep can help your body fend
off infections and illnesses, replenish energy reserves, and help you
wake up feeling refreshed, energized, and ready to take on the day.
What Happens If You Don’t Get Enough Deep Sleep?
“The unintended consequences of
sleep deprivation can be devastating,” says
J. Rico Blanco, MSHA, Certified Director of Sleep Medicine for the American Osteopathic Association.
“Physically, [those who are] sleep-deprived experience fatigue,
low energy, and lack of alertness,” he explains.
When it comes to your mental state, Blanco says a lack of sleep can affect
your overall mood, which can lead to being
easily agitated, upset, or depressed. “Both contributing factors negatively affect
your overall health, and when you combine lack of energy and depression,
it equals unsatisfactory health outcomes,” he adds.
“Sleep deprivation, even one night, is known to have negative effects
on cognitive function and physical function and performance,” explains
Vernon Williams, MD, board-certified neurologist, sports neurologist, and founding director
of the Center for Sports Neurology and Pain Medicine at Cedars-Sinai Kerlan-Jobe
Institute in Los Angeles. “There are also significant effects on
mood and impulse control with resulting disinhibition,” he adds.
Even if you get the recommended total hours of sleep each night, too little
time spent in the deep sleep stage can leave you feeling groggy, drained,
and tired. That’s why your body needs slow-wave sleep the most.
Unfortunately, it’s also the stage we naturally
spend less time in as we age, which explains why so many of us describe ourselves as “light
Over time, Dr. Williams says insufficient deep sleep is felt to have negative
effects on the
glymphatic system, which is a kind of maintenance system that helps clear your brain of
proteins and toxins such as tau and amyloid (which are implicated in some
neurodegenerative conditions). “Poor or disordered sleep during
the middle-age years has been associated with increased risk of dementia
as you age,” he adds.
How Many Hours of Deep Sleep Do You Need?
seven to nine hours of sleep per night is a standard recommendation for adults, it doesn't guarantee that
you'll be getting a specific amount of deep sleep. Plus, there’s
no one-size-fits-all or magic number of sleep hours that works for everybody.
To get a good idea of how many hours of deep sleep you need, we first need
to look at the percentage of time you spend in each sleep stage. NREM
stage 1 is short and light. In fact, you can expect to spend only a few
minutes here, or about 5 percent of your total sleep time, before moving
into stage 2, according to the Cleveland Clinic. While you’ll still
be in the light sleep phase of the night, stage 2 is deeper than stage
1, and accounts for about 45 percent of your sleep hours. Once you cycle
through stage 2, it’s off to the good stuff.
Deep sleep, which, again, is considered NREM stage 3, makes up about 25
percent of the total sleep time for adults. In other words, if you average
seven to eight hours of shut-eye a night, your deep sleep should translate
to about one to two hours of this time.
Finally, REM sleep makes up about 25 percent of your total time, similar
to NREM stage 3. It’s also where you’ll spend most of your
Keep in mind that these are rough guidelines, and individual sleep needs
can vary. Some people may naturally have more or less deep sleep, and
factors like genetics, lifestyle, and sleep disorders can influence it, too.
How Can You Tell How Much Deep Sleep You’re Getting?
So, how do you know if your time spent in bed is comparable to the guidelines?
It’s hard to nail down specifics, but wearable smartwatches, bracelets,
or headbands can give you a rough estimation by collecting and analyzing
your snooze stats.
That said, to get exact data about your Zzzs, you need to do a medical
sleep study, according to
Johns Hopkins Medicine. These studies monitor brain waves to analyze your sleep throughout the night.
The Connection Between Deep Sleep and Exercise
Deep sleep helps us feel rested and ready for the day. It’s also
when your body repairs and rebuilds tissues, strengthens the immune system,
and consolidates memories. That’s why maximizing our time in this
stage is so important.
One way to help increase the odds that you’ll increase and improve
deep sleep is with exercise. Experts from
Johns Hopkins Medicine suggest that moderate aerobic activity increases the amount of slow-wave
sleep you get, with some people noticing a difference that same night
after engaging in 30 minutes of exercise.
Blanco says adopting a new exercise program increases the likelihood of
getting a better night’s sleep. That’s because getting active
increases your ability to sleep more soundly, as our bodies require more
sleep to restore and build muscle. Exercise also enhances self-efficacy,
which, Blanco says, may increase overall life satisfaction and remove
anxiety that can plague you when you’re trying to nod off.
Exercise also appears to improve the
glymphatic system functions mainly during sleep, “which has significant potential
ramifications for chronic neurological disorders such as Alzheimer’s,
dementia, and Parkinson’s Disease,” Dr. Williams explains.
What’s more, improvements to this system may also optimize general
neurologic function throughout your lifetime. (Translation: Snoozing can
help keep your brain healthy.)
And while exercise is known to improve the speed at which you fall asleep
and improve sleep quality, Dr. Williams says it’s important to note that
exercise too close to bedtime can impair sleep onset. (Just avoid vigorous exercise
one hour before you hit the hay.)
Benefits of Deep Sleep for Physical Recovery
“Deep sleep is a necessary component of a healthy, balanced lifestyle,”
Blanco says. Whether you’re a little active or very active, Blanco
says everyone can benefit from a good night’s sleep. “Sleep
should be restorative, allowing your body to repair muscle cells and replenish
your overall health,” he adds. As mentioned above, deep sleep is
crucial for recovering from a workout and getting your mind and body ready
for the next one.
What’s more, sleep isn’t simply a “brain rest”
state, Dr. Williams explains. “There are active physiologic processes
taking place in the body that require sleep, particularly its relationship
to circadian rhythms,” he says. “These processes affect nearly
every cell, organ, and system in the body.”
The Role of Nutrition and Lifestyle in Deep Sleep
Eating too close to bedtime can be a tricky endeavor when it comes to your
Zzzs. Choose certain foods, and you’ll be up tossing and turning
with heartburn or indigestion. Sip on a caffeinated beverage late in the
afternoon, and you risk staring at the ceiling counting sheep. But when
it comes to deep sleep specifically, why does nutrition play such a critical
role in how much we get?
Well, according to Dr. Williams, eating too close to bedtime can negatively
affect deep sleep, as can caffeine and alcohol intake. Another area of
concern, he says, are extreme diets that place you at risk for nutrient
deficits and dehydration, which can negatively impact slow-wave sleep.
The good news is that healthy nutrition and
lifestyle habits can optimize slow-wave sleep. “Eating a balanced diet, maintaining
good hydration, regulating the time of food consumption, and avoiding
heavy meals for a few hours prior to sleep onset is a good place to start,”
Dr. Williams says.
Blanco agrees that dietary choices and lifestyle factors can positively
or negatively affect deep sleep. “As a caffeine enthusiast, I have
found that limiting my coffee intake to one to two cups daily before 1:00
PM allows me to fall asleep quickly and sleep more soundly,” he
says. “If I stray from this routine and consume caffeine later in
the day, my sleep becomes disruptive, and the effects can linger for a
day or two.”
Blanco also says eating meals that are overly processed, as well as foods
high in sugar or saturated fat, has an impact. One way to get a better
night’s sleep, Blanco says, is to adopt a balanced diet. For example,
he recommends the
U.S. Department of Agriculture's (USDA) MyPlate five food groups, which includes fruits, vegetables, grains, protein,
and dairy. “A solid foundation of foods [that are] high in fiber,
nutrient-dense, and fresh can help your body restore and replenish resources
used during the day,” Blanco says.
Beyond food and nutrition, Blanco really stresses that what we do daily
directly affects our sleep. “I encourage people to live a life they
are passionate about because that feeds the mind and body and can usher
in a better night's sleep.”
While getting seven to nine hours of sleep is a good general guideline
for most adults, the number of sleep cycles you experience and the time
spent in each stage, including deep sleep, can vary widely. That’s
why focusing on overall sleep quality and making sure you get enough total
sleep to feel rested and alert during the day is key. If you find you’re
more tired or fatigued than normal, or you’re experiencing sleep
disturbances despite getting what you believe to be an adequate amount
of sleep, it may be worth consulting a healthcare professional or sleep
specialist to evaluate your snooze patterns and address any potential