Is 6 Hours of Sleep Enough? 5 Reasons Why It’s Not

You may feel fine after six hours of sleep, but really, everything from your energy levels to your health and mental performance will be impaired.
Written by
Jeff Kahn, M.S., Rise Science Co-Founder
Reviewed by
Jamie Zeitzer, PhD, Rise Science Scientific Reviewer
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We bring sleep research out of the lab and into your life. Every post begins with peer-reviewed studies — not third-party sources — to make sure we only share advice that can be defended to a room full of sleep scientists.
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Man sleeping at desk in office feeling sleepy after 6 hours of sleep

Did you know that there are only three genes that let you sleep four to six hours and still feel in top form the next day?

Scientists at the University of California, San Francisco (UCSF) discovered that the NPSR1 gene mutation allows you to get by on four to five and a half hours of sleep, with the added bonus of warding off memory problems associated with sleep deprivation. Similarly, those with the DEC2 and ADRB1 gene mutations need only five to six hours per night.

The catch: Only an infinitesimal minority are blessed with the short-sleep genetic material. And, what’s more, just because you have one of these mutations doesn’t mean you’re guaranteed to have short sleep.  

As Dr. Thomas Roth says in Matthew Walker’s book, Why We Sleep, “The number of people who can survive on five hours of sleep or less without any impairment, expressed as a percent of the population, and rounded to a whole number, is zero.” Case in point: The UCSF researchers highlighted that the NPSR1 gene mutation “is exceedingly rare, occurring in fewer than one in 4 million people.”

That brings us to the question of today’s post, “Is six hours of sleep enough?” Unless you’re already biologically equipped with a genetic cheat sheet for short-sleeping - and the mutation is active - six hours of sleep just isn’t sufficient.

Below, we’ll dive into why you might feel fine on six hours of sleep, what it’s doing to your brain and body, and how the RISE app can work out how much sleep you actually need.

Is 6 Hours of Sleep Enough?

Six hours of sleep is very likely not enough for you to feel and perform your best. Here are five reasons why six hours of shut-eye just doesn’t cut it. 

1. Your Sleep Need is Definitely More Than Six Hours

RISE app screenshot showing how much sleep debt you have
The RISE app can work out how much sleep debt you have.

To the masses, six hours of sleep seems to be a fairly reasonable amount to squeak by compared to four or five hours of sleep. After all, a quick Google search will show some sleep guidelines recommend getting around six to eight or six to seven hours of sleep per night. (Although the National Sleep Foundation’s guidelines say healthy adults need seven to nine hours, not six.). 

But sleep guidelines are exactly that: guidelines. They don’t take into account individual differences, and they’re often based on studies looking at the amount of sleep people get, not what they actually need. What’s more, they’re often based on self-reported data, too, which is notoriously inaccurate

And, unfortunately, the short-sleep gene is rare. You’re more likely to be struck by lightning than you are to possess the gene that allows you to sleep six hours a night with minimum ill effects. A large majority of us will have a sleep need that’s more than six hours. 

Heads-up: Your sleep need is the amount of sleep you need each night. It’s determined by genetics, just like height and eye color. 

One study found the average sleep need stands at 8 hours and 40 minutes per night (plus or minus 10 minutes or so). What’s more, a not-insignificant percentage of the population (13.5%) may need a longer sleep schedule of nine hours or more.

As such, just meeting the standard six to eight hours of sleep is likely not enough for meeting your individual sleep need. 

How do you find out your sleep need exactly? There are two ways: 

The manual way: Try waking up without an alarm clock for at least a week and track how long you slept for each night. This method can be tricky for a few reasons: 

  • First, you need to find a week where it’s possible for you to forgo the alarm clock — a luxury most of us just don’t have.
  • Second, it’s hard to tell how long you spend sleeping each night. We often forget about sleep efficiency, which takes into account the time you take falling asleep and being awake during the night. This includes the phenomenon of retrograde amnesia, where you forget the time just before falling asleep and the sub-10-minute micro-awakenings throughout the night. The result is, we tend to inflate our estimated sleep duration. Six hours in bed isn’t six hours of sleep.
  • And thirdly, if you end up sleeping for much longer than usual, it’s hard to tell if this is due to needing more than six hours of sleep a night, or because you’re paying back sleep debt (more on that in a moment). You may also temporarily sleep for longer when you’re sick or have just done very intense exercise. 

The accurate way: Side-step all of these issues and take the guesswork out of figuring out your sleep need by turning to the RISE app. RISE uses a year’s worth of phone use behavior and proprietary sleep-science-based models to calculate your sleep need down to the minute. Learn more about RISE here.

Why is it so important to know your sleep need? When you don’t meet your sleep need, you start building up sleep debt, the amount of sleep you owe your body. In the RISE app, we measure this over the past 14 nights. 

The more sleep debt you have, the more your energy, productivity, and overall mental and physical health and well-being will be impacted. Your risk of heart disease, obesity, and depression goes up, all by not getting the sleep you need. 

RISE can also work out how much sleep debt you’re carrying.

RISE users on iOS 1.202 and above can click here to view their sleep need.

RISE users on iOS 1.202 and above can click here to view their sleep debt.

2. You Misread Daytime Drowsiness

You don’t need to be full-on snoring at your work desk to realize six hours of sleep isn’t cutting it for you. Simply experiencing mild daytime sleepiness is a sign that your body is already suffering from a lack of sleep.

As William Dement, one of the founders of the field of sleep medicine, often quoted, “Drowsiness is red alert.”

Other warning signals of sleep deprivation include nodding off the moment your head touches the pillow, the overwhelming urge to nap at times during the day that aren’t your natural dip in energy in the afternoon, and morning sleep inertia (or grogginess) that seems longer and more intense than usual. (And, as we explain below, another way to “misread” daytime drowsiness is to think your perceived lack of daytime drowsiness means you’re adequately slept, when in fact you’ve subjectively adapted to sleep loss.)

We’ve covered the connection between sleep and daytime energy here.

3. You Can’t “Hack” Sleep

As much as we’d all love to have more time in the day, you can’t hack sleep to make six hours work for you if your body needs more shut-eye than that. 

The human body is biologically built to get the sleep it needs in the form of sleep cycles.

Each sleep cycle consists of non-rapid eye movement (NREM) sleep and REM sleep. NREM sleep is further split into three stages of sleep, whereby stages 1 and 2 are light sleep while stage 3 is deep sleep.

Everyone cycles through all stages of sleep about four to six times per night — depending on your sleep need — and spends roughly 1.5 hours in each cycle. 

But our sleep cycles aren’t identical throughout the night. We spend more time in deep sleep in the first half of the night and more time in REM in the second half. 

While 20-25% of our total nightly sleep is spent in REM (assuming we meet our need), REM sleep lasts for only 10-15 minutes in the first sleep cycle. In the last cycle, it might last for up to an hour. That means by the fifth or sixth sleep cycle, which coincides with the early to late morning hours (depending on when you went to bed), you are now deep in REM-rich sleep. 

While it’s tempting to think that cutting your nightly sleep short by two hours (say, by waking up six hours into your total sleep need time of eight) means you’ve forgone only 25% of your nightly sleep, this sleep stage imbalance across the night means you’re actually losing 60-90% of your REM sleep need. 

It also works both ways. If you wake up at 8 a.m., but went to bed two hours later than usual at 2 a.m., you lose a significant amount of deep NREM sleep. 

Short-changing your brain of either REM or deep sleep, both of which serve important and distinct functions, has myriad immediate and longer-term consequences to your health and wellbeing. 

Healthy testosterone levels, for example, depend on getting enough early-morning REM sleep. One study found that after sleeping five hours a night for eight nights — something that’s not all too uncommon for some of us — participants had 10% to 15% lower testosterone levels. Another study found participants had lower morning testosterone levels after just one night of sleeping 4.5 hours. (Learn more about the link between sleep and testosterone here.)

And as further proof of how little we can control our sleep architecture (how our brains move through sleep stages across the night), our sleep patterns change again when we try to survive on less sleep than we need. One or more nights of sleep loss means the human brain retains deep sleep at the expense of stage 1, stage 2, and REM sleep. 

When you eventually do get more sleep, your brain self-optimizes and you may experience REM rebound, when your body gets more REM sleep than usual to make up for all that it’s lost out on. But this comes at the expense of the other important sleep stages. 

All this is to say that you can’t hack sleep, control your sleep architecture, or get the benefits of a full night’s sleep in just six hours if that’s not your baseline need. The best sleep hack out there? Getting enough sleep for you. 

4. You Subjectively Adapt to Objective Downgrades

RISE app screenshot showing your energy peaks and dips
The RISE app can predict your circadian rhythm each day.

Perhaps the most insidious aspect of sleep loss is that you subjectively adapt after one (or several) nights of poor sleep. That means you might get six hours of sleep and feel fine, so you think this is enough shut-eye for you. But really, your energy levels and performance are suffering without you even knowing.

The reason behind this is two-fold.

Firstly, your circadian rhythm (the internal body clock that dictates your energy peaks and dips) operates independently of your sleep drive (your need for sleep). We all experience two peaks in energy throughout the day, one in the morning and one in the late afternoon or early evening, and a dip in energy in the afternoon (think your afternoon slump) and before bed.  

Even if you’ve underslept your sleep need last night, the energy surge during your peaks can mask the effects of sleep deprivation. The downside is that your energy peaks could have soared higher if you had gotten enough shut-eye in the first place, and your dips will now feel much lower.

Your subpar energy levels and slower reaction time begin to feel normal. When in reality, as objectively measured, every aspect of your daytime functioning downgrades in terms of your emotional, physiological, and cognitive performance.

Secondly, short sleeping hikes up your cortisol production to unhealthy levels. As an alertness-promoting hormone, excess cortisol misleads you into thinking you’re doing fine on six hours of sleep as you don’t feel tired. But you will still see the consequences of sleep deprivation. 

Feel fine on six hours of shut-eye? Check RISE to see how much sleep debt you’re carrying, you may be surprised to see how much sleep you owe your body. We recommend keeping sleep debt below five hours for maximum energy and performance.

RISE can also predict your circadian rhythm each day, so you can the timings of your peaks and dips in energy. 

RISE users on iOS 1.202 and above can click here to see their upcoming energy peaks and dips on the Energy screen.

5. You Aren’t Productive With the Extra Hours of Wakefulness

What would you do with two or so extra hours each day? Maybe you’d get more work done, spend time with family, or practice a hobby. It’s tempting to cut sleep short to get these extra hours in the day, but most of us won’t spend that time doing anything productive as we’re simply too sleep deprived. 

The sleep debt you build up by only getting six hours of sleep will take a hammer to your daytime productivity, emotional processing, and overall well-being. Consequently, even the simplest task on your to-do list can feel like a Herculean effort, you won’t be your best with family, and it will be much harder to motivate yourself to go to the gym, let alone exert yourself while you’re there.

To really be more productive, you need to get enough sleep for you. We’ve covered more ways to be more productive here.

Is 6 Hours of Sleep Bad for You?

So far, we’ve (hopefully) convinced you that six hours of sleep isn’t enough — unless you’re one of the aforementioned very lucky, but very few and far between, short sleepers by nature.

If you need more proof, here’s what science says happens to you when you get six hours of shut-eye. 

Acute Sleep Debt

Acute sleep debt (measured in the RISE app over a 14-day window) stops you from feeling, functioning, and even looking your best the next day. Pulling an all-nighter impairs your cognitive skills akin to having a blood alcohol level (BAC) of 0.10%, higher than every state’s legal limit.

But you don’t have to stay up for 24 hours to feel these effects. Slightly missing your sleep need over several nights can add up. Sleeping for only seven hours, when your sleep need is eight hours, over 10 consecutive nights will make your brain as impaired as it would if you had not gone to bed at all last night, even though you may not feel that way when you wake up. In fact, the symptoms of sleep deprivation are similar to the symptoms of concussion.

To give you more cause to meet your sleep need tonight, one study found that sleeping for only six hours or less means you’re four times more likely to catch a cold than if you had slept for seven hours or more. 

Another reason? Two consecutive nights of less than six hours of sleep has been associated with a decline in performance that lasts for six days.

Chronic Sleep Deprivation

When you give acute sleep debt a chance to roll over many months and years, it becomes chronic sleep deprivation. And this comes with many unwanted side effects.

As well as no energy, you’ll be upping your risk of physical and mental health issues, possibly due to high cortisol levels. Sleep deprivation messes with other hormones, too, including the aforementioned testosterone.

Constantly undersleeping your sleep need intensifies your risk of chronic medical conditions, such as type 2 diabetes, cardiovascular disease, and high blood pressure. It also weakens your immune system.

Unfortunately, the negative effects don’t stop there. People who regularly sleep for six hours or less tend to have a higher body mass index (BMI), fat percentage, and abdominal circumference than those who sleep for seven to eight hours. So, your insufficient sleep can increase your odds of weight gain and obesity.

And a 2022 study found sleeping for five hours or less at ages 50, 60, and 70 was associated with a higher risk of multimorbidity, or having two or more long-term health conditions. Remember, if you spend six hours in bed, you’re probably not sleeping for six hours. Your real sleep number may well be five!

Finally, a 2023 study found sleeping for six hours or less was associated with higher odds of having a medical condition, including diseases of the nervous system, musculoskeletal system, digestive system, and circulatory system, as well as mental and behavioral diseases.

Stop Sleeping 6 Hours; Start Meeting Your Sleep Need

Many of us are tempted to get more time out of the day by sleeping for just six hours a night. But you simply won’t feel or perform your best with that little sleep, let alone be protecting your long-term good health. 

But we also know getting six hours isn’t always an active choice. Perhaps a demanding work schedule is barring you from a good night’s sleep. Or maybe your newborn hasn’t gotten the sleep memo and often wakes up in the middle of the night. Your lack of sleep could also be due to an underlying medical condition or sleep problem. For example, various sleep disorders like obstructive sleep apnea, restless leg syndrome, and sleepwalking disrupt sleep. 

Sometimes there is something we can do about it, though. And that’s where sleep hygiene comes in. These are the daily sleep habits you can do to help you fall and stay asleep each night. If we’ve convinced you to start getting more than six hours of shut-eye a night, the RISE app can help.

RISE calculates your personal sleep need by using the sleep and activity data on your phone measured over the last 365 nights. It also reveals your running sleep debt on the Sleep tab to show if you’re getting too little sleep (aim for five or fewer hours of sleep debt). To start getting more sleep, the app can guide you through 20+ sleep hygiene habits to help you fall and stay asleep, making it easier to meet your sleep need. 

For example, adding the “Melatonin Window” habit to your Energy Schedule tells you the best time to go to bed for better sleep that night (melatonin is your body’s natural sleep hormone, going to bed during this roughly one-hour window will help you fall and stay asleep). Pair it with the “Evening Routine” habit to schedule your bedtime routine right before your Melatonin Window, so that you can relax into sleep and meet your sleep need more easily.

As you evolve from getting six hours a night to getting your true sleep need, give yourself grace and time to make that transition. If you can, take daytime naps to pay down sleep debt. RISE tells you the exact window of your afternoon dip so you know when’s the best time to get some extra shut-eye.

Resetting your sleep schedule won’t be an overnight transformation, but the effort will be absolutely worth it. Download the RISE app today, so you can start feeling and functioning at your best.

Summary FAQs

Is 6 hours of sleep enough for one night?

For many of us, six hours of sleep is not enough for one night. Scientific evidence indicates the average sleep need is around 8 hours and 40 minutes per night (plus or minus 10 minutes or so), with a not-insignificant percentage of the population (13.5%) requiring nine hours or more of sleep time.

Is 6 hours of sleep enough for a teenager?

Sleep boards such as the National Sleep Foundation and the American Academy of Sleep Medicine agree that six hours of sleep is not enough for a teenager. Their guidelines suggest a longer sleep duration of eight to 10 hours. This is in line with other research on the average sleep need for healthy young adults.

Is 6 hours of sleep enough to build muscle?

Six hours of sleep isn’t enough to build muscle if your body needs more sleep than that (which most of us do). Research shows that sleep deprivation, even for one night, is enough to reduce muscle protein synthesis by 18%, so you’re more likely to experience muscle loss than growth.

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Over the past decade, we've helped professional athletes, startups, and Fortune 500s improve their sleep to measurably win more in the real-world scenarios that matter most.

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