You’ve probably heard about financial debt, but what about sleep debt? Before you dismiss it as a myth or even as a term made up by sleep supplements and mattress companies, sleep debt is real. And if you’re like most of us, there’s a good chance you’re in the red.
Sleep debt refers to how much lost sleep you have under your belt in the past 14 days and comes with significant effects to how you feel and function while awake. Instead of viewing it as a honor badge of hustle culture, take note that the Centers for Disease Control and Prevention (CDC) has proclaimed sleep insufficiency a “public health epidemic.”
As such, it’s really important to know how much sleep debt you have. The problem: it isn’t that easy to calculate your sleep debt, as you’ll see below. Fret not, we’ll reveal the one tool that does measure it to help bring you back into the black.
Sleep debt is the amount of sleep you’ve missed in the past 14 days relative to your sleep need (more on sleep need in the next section). It’s a concept pioneered by the recently deceased giant of sleep medicine, Dr. William Dement, who was well-known for his mantra, “Drowsiness is red alert.” In other words, the slightest bit of tiredness when you’re awake is an indication you’re sleep-deprived and performing sub-optimally.
Contrary to popular belief, it is sleep debt researchers agree determines how you feel and function each day, not “quality sleep,” a term for which there’s no scientific consensus definition. This means, you don’t need to worry about how much time you’ve spent in REM sleep or how much deep sleep you need. Instead, getting sufficient naturalistic sleep — i.e., meeting your sleep need via naturalistic sleep (more on both later) — is quality sleep. That’s why the only sleep score that matters is sleep debt.
Just like your height and eye color, your sleep need is genetically determined.
The average sleep need stands at 8 hours and 10 minutes per night, plus or minus 44 minutes, with 13.5% of the population needing a longer sleep schedule of 9 hours or more. When you don’t meet your nightly sleep need, you accrue sleep debt. For instance, if your sleep need is nine hours but you only had 7 hours of sleep two nights in a row, you would have accrued four hours of sleep debt. Since sleep debt is calculated over a 14-day horizon, you can see how hours of missed sleep add up quickly.
To better understand sleep debt, we have to understand how sleep “works”. For that, we turn to the Two-Process Model of Sleep Regulation, first established by sleep scientist Alexander Borbély in the 1980s. One part of the model – your circadian rhythm – explains sleep timing or when your body wants to sleep or be active. The second part of the model describes the sleep homeostatic process, which for our purposes here can be understood as how much sleep your body needs.
Sleep homeostasis, or any homeostatic process, is about balance: think of it as a seesaw that wants to be level. During wakefulness, a drowsiness-inducing compound called adenosine builds up in your brain, tilting the homeostat to one side. At bedtime, this “sleep pressure” is at its climax. When this coincides with the “sleep gate” trough of your circadian rhythm, sleep comes easily. If you meet your sleep need, adenosine fully dissipates and rebalances the sleep homeostat.
On the other hand, if you don’t meet your need, leftover adenosine stays in your system. This leaves the seesaw unbalanced, making you feel groggier than usual. In essence, you don’t feel and function at your best when sleep debt’s hanging over you — more on that in the next section. (For a more in-depth explanation of Borbély’s Two-Process Model, head to our Sleep Guide.)
Sleep debt has widespread ramifications on your waking life, both in the short and long term. For clarification, acute sleep debt is measured in a short two-week to one-month time frame (it’s a 14-day window in the RISE app). On the other hand, chronic sleep deprivation refers to not getting enough sleep on a regular basis over months and years.
Those ramifications, however, can be hard to see at first. In Dr. Dement’s canonical sleep study on the effects of sleep restriction, participants underwent seven nights of sleep restriction and two nights of recovery sleep. Using self-rated assessments, test subjects reported that daytime sleepiness immediately increased after sleep restriction and plateaued after four days. Meanwhile, the multiple sleep latency test (MSLT), an objective test that measures how fast you fall asleep, discovered that elevated sleepiness continued until the last day of sleep restriction. Moreover, the study showed that sleep deprivation had a “cumulative effect on daytime well-being that persists” throughout the sleep restriction period even though study participants stopped perceiving declines in their own alertness after a few days.
This difference between self-reported and objective sleepiness highlights how dangerous sleep debt is.. After a few days of lost sleep, you subjectively adapt as your downgraded cognitive performance feels “normal.” If you merely meet your sleep need on your recovery nights without getting extra sleep for prior sleep loss, your brain will continue to operate at a reduced capacity as you’re not actively paying down sleep debt.
In the short term, expect inevitable downgrades to your emotions, physical health, and cognition. Think poor mood, a weakened immune system, and reduced attention span, to name a few. In the long term, chronic sleep debt spells even more trouble for your overall well-being. Brace yourself for an increased risk of metabolic health issues like obesity, type 2 diabetes, and high blood pressure on top of weight gain. You’re also more likely to develop heart disease, sleep disorders like sleep apnea, mental health problems, stroke, cancer, and other chronic illnesses.
Given the gamut of sleep-related declines and health problems, it makes sense to prioritize low sleep debt, which we will show you how in later sections. That said, it’s unrealistic to expect zero hours of sleep debt as life sometimes throws us curveballs.
Instead, strive for a sleep deficit that’s five hours and below. It’s the sweet spot for feeling and functioning at your best on most days, or as close to it as possible.
There are a few ways to answer the question, “How much sleep debt do I have?”, some more accurate than others.
Before we go into the specifics, you first need to know your individual sleep need to have a baseline for how much sleep you’ve skipped out. That's not to say you should rely on generic recommendations by sleep boards like The National Sleep Foundation. The reason is these generalized guidelines describe what counts for a “normal” amount of sleep across the population based on what people are getting but not what they need. Thus, they aren’t prescriptive at the individual level because everyone's biological need is unique.
Instead, try one of these two methods:
Ahead, we share three ways to determine how much sleep debt you have. Bear in mind that the first two methods are subjective and may not guarantee 100% accuracy.
A noon self-check-in basically refers to making it until noon without a nap or a cup of coffee. If you find yourself reaching for either or feel like you can’t function without them, it’s a sure sign of sleep deprivation.
That said, this way of measuring sleep debt isn’t entirely reliable. This is especially so for habitual coffee drinkers (more than 90% of the adult population in America) who are vulnerable to caffeine dependence. Quitting caffeine cold turkey induces side effects like lethargy that may mislead you into thinking you’re more sleep-deprived than you actually are.
Remember Dr. Dement’s mantra: “Drowsiness is red alert.” While it’s natural to feel tired during the energy dips of your circadian rhythm, experiencing the teeniest bit of drowsiness outside of these dips is a good indication you’re carrying sleep debt.
Be that as it may, Dr. Dement’s earlier study on subjective versus objective levels of drowsiness following sleep loss shows we aren’t accurate judges of how tired we are. So, the actual amount of sleep debt you have may be more or less than what you perceive.
We’ve mentioned how it’s subjectively tricky to rate how sleep-deprived you are, especially by how much debt you carry. Even in professional sleep laboratory settings, sleep debt measurement is both an art and a science. Case in point: Both the MSLT and the Stanford Sleepiness Scale (SSS) are widely used to measure objective and subjective sleepiness, respectively. Yet, each comes with its own limitations.
To illustrate, MSLT often ignores the root cause of objective sleepiness, which in most cases, is due to sleep debt. This test also overlooks microsleeps (brief periods of involuntary unconsciousness) that typically occur during monotonous tasks like driving.
Meanwhile, the SSS is a self-rated assessment in which the individual has to rate their subjective sleepiness every 15-20 minutes. As you can imagine, not only is this tedious for the average person but also unreliable, given our innate inaccuracy when it comes to determining drowsiness.
For these reasons, it’s better to use a tool like the RISE app that makes it easy for you to objectively track your sleep debt. If you recall, RISE passively catalogs your nightly sleep duration without requiring input from you. Weighing this number against your sleep need, RISE efficiently calculates your sleep debt for you.
For the sake of your sleep health, you may wonder if it’s possible to pay back sleep debt. The good news is, yes, you can catch up on acute sleep debt. Case in point: In renowned sleep scientist Gregory Belenky’s famous sleep dose response study, two nights of recovery sleep after a full week of sleeping 4-5 hours per night restored sleep restriction-induced deficits in cognitive performance and mood.
Make up for less sleep in the previous night(s) by out-sleeping your sleep need. Pencil time in for extra sleep in the next few nights or however long you need to pay down sleep debt, as per the Sleep screen in the RISE app. Leverage earlier bedtimes, afternoon naps, and late sleep-ins (but not too late) to get those extra hours of sleep whenever possible.
To keep your sleep debt consistently low, practice good sleep hygiene paired with your circadian rhythm. This is where the RISE app can help. Your Energy Schedule on the Energy screen shows the best times to carry out healthy sleep habits based on your unique chronobiology. For instance, go to bed early within your Melatonin Window and take a power nap during your afternoon dip to pay down your sleep debt.
For the full story on how to use RISE for better sleep for better days, head over to our step-by-step Sleep Guide.
On average, adults need about 8 hours and 10 minutes (give or take 44 minutes or so). Meanwhile, a not-so-insignificant percentage of the population (13.5%) may need nine hours or more. The best way to find out how much sleep you need is to use a tool like the RISE app.
Sleep debt, also known as sleep deprivation, is real. When you don’t meet your sleep need, you accumulate sleep debt, which has real-world impacts on your daytime functioning.
The good news is that you can catch up on acute sleep debt by napping. Meanwhile, the research on recovering from chronic sleep deprivation is less conclusive. Even if you can’t totally reverse the effects of long-term sleep loss, making a real effort to reduce your acute sleep debt is definitely worthwhile.
Common sleep debt symptoms include excessive daytime sleepiness, reduced attention span, slow reflexes, impaired productivity, a weakened immune system, and poor mood the next day. Over time, your overall health deteriorates and exposes you to an increased risk of chronic illnesses.
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