How Much Deep Sleep Do You Need Each Night?

These expert-backed secrets will help you score the right amount of restorative sleep.

Woman Sleeping
Photo: Getty Images

Whether you're wired from a little too much time scrolling on TikTok or stressed after a jam-packed day, you might find yourself lying in bed with your mind racing, struggling to fall asleep. And even once you manage to drift off, you can wake up feeling drained — pretty much the opposite of what you'd hope for, especially when another nonstop day awaits. If this scenario sounds familiar, it's possible you're concerned about the quality of your sleep and whether or not you're getting enough deep sleep.

"Deep sleep is your most restorative stage of sleep," explains Stephanie R. Wappel, M.D., a sleep and pulmonary medicine physician at Greater Baltimore Medical Center Health Partners Pulmonary and Sleep Medicine in Towson, Maryland. "If you aren't getting enough deep sleep, you may not feel as refreshed or restored in the morning." What's more, a deficit in this particular stage of sleep can lead to decreased immunity, impaired hormone regulation, and some cognitive decline, says Dr. Wappel.

Here, experts explain what deep sleep is, how it influences your health, and how to figure out if you're getting enough.

The Stages of Sleep

When you fall asleep, your body moves through several sleep stages before repeating the cycle, explains Marcella Frank, D.O., assistant medical director of the Institute of Sleep Medicine at Deborah Heart and Lung Center in Brown Mills, New Jersey. First comes the light sleep phase, when you're probably still somewhat aware of your surroundings, followed by light slow wave sleep, the stage when your body temperature drops and eye movements stop, which most people spend about half of their total sleep time in, according to Dr. Frank.

Then you enter deep sleep, which is also referred to as slow wave or delta sleep. You'll experience the slowest heartbeat and breathing during this phase, and your muscles are at their most relaxed. Earlier in the evening, within the first stage of each sleep cycle, this phase lasts for about 45 to 90 minutes, but with subsequent cycles, the number of minutes of deep sleep decreases. "I don't think the exact reason why this occurs is clear, but it's likely important for optimal functioning to allow the body and brain to have more restorative sleep during the first half and then more REM sleep during the second half of sleep," says Dr. Wappel.

The final phase is rapid eye movement (REM) sleep, which is when most dreaming occurs. Contrary to what you think you might know about REM, this actually isn't considered a restful sleep stage. In fact, REM is often the sleep phase in which people wake up in the morning.

The Deep Sleep Stage, Defined

Sleep doctors can gauge what sleep stage someone is in by looking at brain waves on an electroencephalogram, or EEG, while the person is asleep, and deep sleep is associated with delta waves — or the slowest waves, explains Dr. Frank.

As you might have guessed, it's harder to wake someone up from deep slow wave sleep compared to other stages of sleep. "This is the stage in which sleepwalking generally occurs, and that's why it is very difficult to wake a sleepwalker," says Dr. Frank. "When someone awakens [during the deep sleep phase] they are often groggy for a while." (Related: This Woman Is Going Viral On TikTok for Her Hilarious Sleepwalking Videos)

A few other key characteristics of this deep sleep phase:

Memories are consolidated during deep sleep.

Each stage of sleep serves a useful function for the brain, although researchers don't completely understand exactly how each stage accomplishes its function, says Dr. Frank.

Your body forms synapses — the connections between neurons (brain and nerve cells) — all the time, especially throughout the day when you are learning new things and your brain and body are active, explains Dr. Wappel. And because so many connections are formed, the signals that nerve cells send through the synapses create a lot of "noise" which can overwhelm your brain, and the signals become unclear. Your brain is then less likely to be able to accurately read the signals. "But deep sleep allows an opportunity for the brain to relax so that these synapses can get cleaned up or fine-tuned, to sharpen the connections and get rid of some of the noise — sometimes this is referred to as 'pruning,'" she notes.

In other words, it's as though your brain is sorting through all your recent memories and deciding which get filed away into long-term memory and which are released or demoted as not as important.

Slow wave sleep affects your hormones, immune system, and blood pressure.

Since the regulation of many vital hormones occurs during sleep, your body relies on deep sleep for optimal functioning, explains Dr. Wappel. Those hormones include insulin, which helps regulate blood sugar by controlling the amount of glucose in your blood; ghrelin and leptin, hormones that tell you you're hungry or full; thyroid hormone, which regulates your metabolism; and the stress hormone cortisol.

Deep sleep "also regulates your immune system's functioning," she notes. "During deep sleep, the blood pressure, heart rate, and breathing rate are lower than during wakefulness and during other stages of sleep, which gives the immune system and other organ systems an opportunity to strengthen and recharge while the brain and body are otherwise 'relaxed.'"

Similarly, blood pressure and glucose levels will decrease during deep sleep. "This is normal and is part of the body's way of slowing down the system so it can recharge — it's why deep sleep is considered restorative sleep," explains Dr. Wappel. (Related: A Sleep Expert Answers All the Questions You Have About Zzz's)

How Much Deep Sleep You Should Get a Night

The amount of deep sleep you need is very individual, says Sudha Tallavajhula, M.D., a neurologist with UTHealth Neurosciences and medical director of the Neurological Sleep Medicine Center at TIRR Memorial Hermann in Houston.

In general, the average adult spends about 13 to 23 percent of the night in deep slow-wave sleep, and that seems to be an adequate amount, says Dr. Frank. "Studies have indicated that the average adult needs seven to eight hours [total] per night, and it seems that spending 13 to 23 percent of that time in deep sleep is normal" and theoretically, that's enough for optimal functioning, adds Dr. Wappel. (That works out to anywhere from 55 minutes to one hour and 50 minutes, in case you're wondering.)

How to Know If You're Getting Enough Deep Sleep

While deep sleep is important, there's no need to get super hung up on results from wearable sleep monitoring devices, for example. "Getting 'good' sleep numbers is not the ultimate goal," says Dr. Tallavajhula. "The parameters used for calculating deep sleep are different among manufacturers and may not necessarily mean the same thing."

"The sleep trackers are very helpful to get a sense of general sleep patterns and how restful one's sleep is, but they are not a substitute for an EEG which shows the brain waves and allows you to definitively distinguish sleep versus wake and the different stages of sleep," adds Dr. Wappel.

It's more helpful to pay attention to whether you're waking up feeling exhausted or just not refreshed, which indicates you're probably not getting enough sleep, period, says Kendra Becker, M.D., a sleep medicine specialist and internist at Kaiser Permanente in Fontana, California. "Make sure you're getting enough sleep — that's seven to eight hours a night — in general," she notes. "And the deep sleep will come."

Of course, even if you always clock eight hours, you might still experience trouble getting enough deep sleep if your environment isn't conducive to it, points out Dr. Wappel. "Sleeping in a disruptive environment — for example, with TV and other electronics emitting blue light that the brain interprets as sunlight — can impair your sleep quality and prevent you from getting into deep sleep," she notes.

Healthy lifestyle habits — e.g. maintaining a well-balanced diet, exercising regularly, using that meditation app, and avoiding blue light from tech devices — should set your brain up for enough deep sleep, says Dr. Frank. You might also benefit from maintaining a steady sleep schedule, keeping the light and temperature in your room low, and avoiding caffeine and alcohol prior to bedtime, adds Dr. Tallavajhula.

And if you've made an effort to up your overall sleep and are still waking up beyond zonked, it may be time to check in with your primary care physician.

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