There's More To Feeling Rested Than Getting Eight Hours of Sleep

How much time you spend in REM and deep sleep is crucial to feeling rested when you wake up the next day.
How Much REM Sleep Do You Need Less Than You Think
Michael Houtz; Getty Images

It used to be as easy as getting eight hours of sleep a night—period, the end, honk shoo. Then, as technology infiltrated our lives with fitness trackers like Eight Sleep, WHOOP, and Oura Ring, we began to realize that the type and quality of sleep we're getting are important, too. Loosely speaking, Scott Kutscher, MD, a clinical associate professor of sleep medicine at Stanford University, says that most guys need about seven to nine hours. However, it can vary from person to person.

However, there are also five different stages of sleep, and how much time we spend in each impacts how rested we wake up feeling the next day. These stages are awake, non-REM sleep (NRM) 1, NRM 2, NRM 3 (or deep sleep), and REM (or rapid eye movement sleep). As for how much time we need to be in each type? We consulted experts to weigh in on how much time we spend in different sleep stages, how much sleep we need overall, and the importance of Netflix-free naps.

What is REM vs. deep sleep?

All stages of sleep are essential, but Dr. Kutscher calls light sleep or the sleep in NRM 1 and 2 the "backbone" of your evening, accounting for at least 50 percent of your cycle. The other 50 percent is divided between non-REM deep sleep and REM sleep.

Chris Winter, MD, a neurologist and sleep medicine specialist, likens the different phases of sleep to fats, carbohydrates, and protein as building blocks of your diet. "Which one's most important? Well, I'm not sure you could answer that. Depending on what you need from your body, all three of those things are important and, frankly, essential. So you want to ensure you're giving yourself as much of a leg up as possible to get it all."

Deep sleep

During deep sleep, or "slow wave" sleep, your body is the most at rest. Muscle tone, heart rate, and breathing rate decrease during this stage. It's also when we release most of our growth hormone, so it's imperative for recovery—especially for athletes. This sleep is predominantly accumulated during the first portion of your sleep cycle, something you may have noticed before if you track your sleep wearing a fitness wearable. Typically, when someone says, "I got some good sleep," they get a good chunk of deep sleep. According to the Sleep Foundation, about 20 percent of your sleep is deep sleep.

REM sleep

REM sleep is when we experience much of our dreaming, which most often happens in the last portion of our sleep cycles. During the REM sleep stage, there's variability in heart rate and blood pressure, and we don't regulate our body temperature. According to the Sleep Foundation, REM sleep is responsible for emotional processing, memory consolidation, and brain development, so you don't want to skimp on it, even though it accounts for only about two hours of our total sleep a night.

"If you're going to bed too late, you're most likely missing more slow-wave sleep," says Dr. Kutscher. "And if you're waking up earlier than your body, like with an alarm, then you're likely missing out on REM sleep."

How much sleep do you really need?

Different individuals need different amounts of sleep. The American Academy of Sleep Medicine (AASM) and Sleep Research Society (SRS) recommend that adults obtain seven or more hours of sleep per night to avoid the health risks of chronic inadequate sleep. However, some individuals may need more sleep than others, depending on many factors, including activity levels, age, and illness.

"If you're an elite runner or really training heavily, you're probably gonna need more sleep," says Dr. Winter. "We also tend to sleep more when we're sick since the body works overtime to fight infection and repair itself."

Aim to set yourself up for sleep success by creating a sleep routine, which helps your body and mind prepare the best way possible for the rest ahead and may include sensory cues like smells, dimming the lights, and putting electronics down in the 30 to 60 minutes before sleep.

If your need for sleep increases dramatically without explanation, that constant tiredness—especially with age—could be a reason for concern. "If suddenly at age 45 you feel like you need 13 hours of sleep to be your best, then when you were 35 you felt like seven was perfect, that's a red flag. So anytime you suddenly feel you need more sleep, it's an indication to chat with your doctor."

What happens when you don't get enough sleep?

A late night at the office. Drinks with friends. Staying up past your bedtime to finish season eight of Suits. All of these things increase your sleep debt over time and can contribute to chronic partial sleep deprivation. Chronic partial sleep deprivation is associated with increased impulsivity and decreased positive affect in young adults. Dr. Kutscher says it can also trigger slowed reaction time, reduced concentration, and negatively impact memory and judgment. Since sleep deprivation may not happen all at once, someone may not realize these results as they occur.

Dr. Kutscher recommends, rather than trying to make up for it in bulk (read: a 14-hour sleep on a Saturday evening like Dakota Johnson), making small, more digestible tweaks throughout the week instead.

"When you are shorting yourself 30 minutes to an hour of sleep every night, that accumulates," he says. "So, if you can find time in your schedule to go to bed 15 minutes earlier and wake up 15 minutes later, you've given yourself 30 extra minutes of sleep a day. That adds up to three and a half extra hours of sleep a week, and that could be a big deal."

Do naps matter?

If you're on Team Coffee at 4 p.m., you may want to reconsider. "There is no recovery mechanism that helps sleepiness better than sleep," says Dr. Kustcher. "Caffeine is an inferior product to sleep."

The only risk? Napping too long. Dr. Kutscher recommends a 30-minute nap, which includes the entire period of time when you're horizontal. And if you can't fall asleep? Don't stress. Research shows that resting, being completely disconnected, and not watching Netflix can give you restorative benefits—even if you're not on the express train to Dreamland.

Longer than 30 minutes, you could risk cutting into your sleep time for the evening. You should never plan to use a nap to replace sleep, advises Dr. Winter. "Naps are a backup, not a strategy," he says.