What Is “Sleep Debt” and What Can You Do About It?

By Dr. Ryan Neely, Ph.D.

You may or may not be familiar with the term “Sleep Debt,” but the term implies a deficit of sleep and, ominously, implies that it is something that will become due. The core concept is simple enough - sleep debt occurs when the sleep that you get is less than the sleep your body needs. However, scratch the surface of this concept and many questions emerge: how do you know when you’ve incurred a sleep debt? What happens when you have one? Can you adapt to shorter sleep times? How can you “pay it off?” In this post, we’ll explore this concept and hopefully clarify the answers to these questions, as well as highlight what we do and don’t yet understand about sleep debt.?

How do you know you’ve got a sleep debt?

As addressed above, sleep debt is a negative difference between the amount of sleep you receive and the amount of sleep you need. These two numbers aren’t that easy to come by, however. As a general rule of thumb, the American Academy of Sleep Medicine has endorsed general guidelines for the amount of sleep a person needs in each 24 hour period, based on their age:

While these numbers are helpful, the reality is that every individual will have a slightly different need for sleep quantity that may change depending on life circumstances (for example, if you are recovering from illness or injury). One way to gauge whether you’ve incurred a sleep debt is to look for signs of insufficient sleep. Over the short term, these include cognitive changes, like slower reaction times, decreased alertness, and poor judgment; emotional effects like irritability or depressed mood; and perhaps obviously, feelings of sleepiness, unplanned naps, and involuntary moments of falling asleep (known as microsleeps)3.Experiencing some or all of these symptoms could be a sign that you need more sleep.

Determining the total quantity of sleep you actually get is also not exactly straightforward. Just because you go to bed at 10:00 PM and get up at 6:00 AM does not mean that you’ve gotten 8 hours of sleep. To determine the actual sleep duration, you need to subtract the time it takes you to fall asleep, as well as any additional periods of wakefulness you experience throughout the night (the technical term for this is “Wake After Sleep Onset”, or “WASO”). Various types of sleep trackers can be helpful for measuring your total sleep duration, although you’re more likely to get an accurate estimate using a device that measures brain activity directly. Getting a sense for how much you sleep each night can help you measure yourself against the AASM guidelines, as well as help you better determine how much time you need to allocate for sleeping in order to meet them. For some ideas about how to make the most of your time in bed, check out this previous post on sleep interventions.

Can you “adapt” to shorter sleep times?

Another important question related to the notion of sleep debt is whether a person can habituate or “train” themselves to adapt to shorter sleep times. Anecdotally, you may have heard people report a wide range of typical sleep durations. Indeed, studies have shown that habitual sleep durations follow a typical normal distribution, with most people falling inside of a wide range of 5-10 hours4. This range raises the question of whether some individuals simply need less sleep, potentially by adapting to shorter sleep times, or if they are simply carrying a long-term sleep debt. At least one study has suggested that the latter is true - by measuring sleep pressure, researchers at Harvard and the University of Surrey found that individuals with shorter habitual sleep durations carried stronger sleep pressure and, when given the opportunity, compensated by sleeping for longer periods of time5. Indeed, when the same researchers gave adults unrestricted opportunity to sleep across several nights, most young adults eventually settled in at about 8.9 hours, while older adults leveled off at about 7.46. This suggests that people who report habitually shorter sleep may be carrying around a significant sleep debt. However, one question that these studies did not answer was whether there are individual differences in how people handle sleep debt. For example, it may be the case that some people are able to carry a sleep debt without a significant impact on their ability to function.

Consequences of sleep debt and how to pay it off

The short term symptoms of sleep debt are described above - lower cognitive function, emotional changes, and signs of sleepiness. But what about long-term sleep debt? Chronic sleep insufficiency can have more serious consequences, such as accidents (sleepiness is a common cause of car crashes), declining cardiovascular health, suppression of the immune system, obesity, and an overall lower quality of life3.? In general, the risk and severity of these effects is related to the amount of sleep debt a person incurs. Of course, everyone will experience some occasional loss of sleep, so how can you recover, or pay back your debt? It’s incredibly common for people to attempt to “catch up” on sleep over the weekend or days off, when they have fewer obligations and a more flexible schedule. Napping may be another way to try to gain additional sleep. Certainly, these approaches can help to offset some of the sleep missed during the work week. However, a population-level study found that, in general, people don’t add back enough sleep by napping or sleeping in on the weekend to account for their cumulative sleep debt7. Furthermore, a 2-week study of young adults in a sleep lab found that it typically takes about 4 days of unrestricted sleep to fully recover from sleep deprivation, suggesting that a weekend of extra sleep may not be enough to recover fully from a week of late nights and early mornings8. The good news, however, is that this same study also reported that after paying off their sleep debt, these same individuals experienced improvements in their metabolism, immune function, and stress hormone levels. These data suggest that the body is able to quickly rebound from the negative effects of sleep loss when given the opportunity.?

Conclusions

Sleep debt occurs when the sleep you need exceeds the sleep you get. Most adults need about 7-8 hours of sleep each night, which can be measured by using a sleep tracker. Missed sleep can have short-term impacts on your daily functioning, and chronic sleep loss can have more serious health consequences. Carrying sleep debt is common, and the good news is that it’s possible to make up for it by simply getting additional sleep. However, sleeping in on the weekends and taking naps may not be enough to account for a week of deficit. A better strategy is to consistently sleep enough so you can avoid sleep debt altogether. This may be a difficult prospect for many of us with busy lives and multiple obligations - in these cases, making the most of your time in bed is a good way to make sure you’re getting enough sleep. Approaches like Elemind’s that help you to fall asleep faster and restart sleep quickly can improve your sleep efficiency when you’re pressed for time.?

References:

1. Paruthi, S., Brooks, L.J., D'Ambrosio, C., Hall, W.A., Kotagal, S., Lloyd, R.M., Malow, B.A., Maski, K., Nichols, C., Quan, S.F. and Rosen, C.L., 2016. Recommended amount of sleep for pediatric populations: a consensus statement of the American Academy of Sleep Medicine. Journal of clinical sleep medicine, 12(6), pp.785-786.
2. Watson, N.F., Badr, M.S., Belenky, G., Bliwise, D.L., Buxton, O.M., Buysse, D., Dinges, D.F., Gangwisch, J., Grandner, M.A. and Kushida, C., 2015. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, 11(6), pp.591-592.
3. Cirelli, C. (February 2024). Insufficient sleep: Definition, epidemiology, and adverse outcomes. In R. Benca & A. Eichler (Ed.). UpToDate.
4. ?Krueger, P. M. & Friedman, E. M. Sleep duration in the United States: a cross-sectional population-based study. Am J Epidemiol 169, 1052–1063, doi: kwp023 10.1093/aje/kwp023 (2009).
5. Klerman, E.B. and Dijk, D.J., 2005. Interindividual variation in sleep duration and its association with sleep debt in young adults. Sleep, 28(10), pp.1253-1259.
6. ?Klerman, E. B. & Dijk, D. J. Age-related reduction in the maximal capacity for sleep--implications for insomnia. Curr Biol 18, 1118–1123, doi: S0960-9822(08)00804-X 10.1016/j.cub.2008.06.047 (2008).
7. Leger, D., Richard, J.B., Collin, O., Sauvet, F. and Faraut, B., 2020. Napping and weekend catchup sleep do not fully compensate for high rates of sleep debt and short sleep at a population level (in a representative nationwide sample of 12,637 adults). Sleep Medicine, 74, pp.278-288.

Kitamura, S., Katayose, Y., Nakazaki, K., Motomura, Y., Oba, K., Katsunuma, R., Terasawa, Y., Enomoto, M., Moriguchi, Y., Hida, A. and Mishima, K., 2016. Estimating individual optimal sleep duration and potential sleep debt. Scientific reports, 6(1), p.35812.

This article was originally published to the Elemind Blog.

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Dr. Ryan Neely, Ph.D. is VP of Science and Research at Elemind. He studied the neural basis of learning during neuroprosthetic control while at UC Berkeley before embarking on a career developing novel therapeutics and medical devices. He is focused on innovation at the interface of biology and technology.