Sleep Debt – Can you catch up? Or are you just dreaming?

We all know that sleep is important (but if you don’t, check out episode 3 or episode 8 for previous discussions about sleep). Now I’m not here to bore you to sleep with extraneous details about slow-wave EEG patterns in different phases of sleep (though that can be exciting!), but I want to talk about a much more prevalent issue for most of us– sleep debt.

What is Sleep Debt?

Simply speaking, sleep debt (often termed potential sleep debt or PSD in research) is an estimate of the amount of sleep you are actually getting, subtracted from the amount of you should optimally be getting.

Potential Sleep Debt (PSD) = Optimal Sleep Duration (OSD) – Total Sleep Time (TST)

First, in order to calculate your sleep debt, we have to estimate an optimal sleep duration. We know from decades of experience that this number typically falls around 8 hours. How? Studies have collected data on thousands of individuals to correlate sleep habits/sleep duration and associated them with outcomes like cardiovascular disease (hypertension, heart attacks), diabetes, mood disorders, and even death. In these studies, the data tends to show a ‘U shaped curve’ with the low point around 8 hours indicating the lowest risk of these poor outcomes. Indeed, short sleepers (usually less than 6-7 hours of sleep in the studies) show higher rates of disease, but interestingly long sleepers (more than 9 hours of sleep) start to show increases in these risks, as well (1).

Luckily, Athlytic makes this easy for us. By tracking your sleep and comparing it to your optimal/goal sleep, you are presented with a running tally of your recent sleep time and an accumulation of your sleep debt.

So, it seems I’ve taken out a loan from the Sandman; does Hypnos offer loan forgiveness?

It’s not easy to stay in a state of sleep surplus, with the demands and pressures of society, work, life, kids, chores, hobbies, so much tends to get in the way.

In one interesting study, participants’ sleep habits and daily activities were very closely monitored, in temperature and light-controlled environments, getting the opportunity to sleep for up to 12 hours, without interruption, while data was then reviewed in order to determine how the participants sleep needs changed when they could essentially sleep as much as they wanted overnight (naps were not allowed, and if a participant fell asleep during the day, they were awoken by the evaluators).

Interestingly, when reviewing the data, the participants tended to spend the first few nights sleeping much more than their average, ultimately reducing sleep over successive nights until they reached a steady-sleep state, closely representing their optimal sleep needs. 

The investigators of the study concluded that the increased sleep needs at the beginning reflected the participants catching up on their sleep debt, and ultimately falling back into a regular rhythm once the debt was repaid. On average, it took about 4 days to see this improvement. (and when I say improvement, I mean it, the reduction in sleep debt was associated in a reduction of symptoms associated with poor sleep, fatigue/tiredness, etc.)(2).

This means the sleep debt can be repaid, but it is not quick - the interest rates are high.

But no need to not stop here. There’s more optimism to be had!

In research as recent as the last month (in a new review publicized at the European Society for Cardiology), researchers found that catch-up sleep on the weekends has the potential to reduce cardiovascular disease by almost 20% (3)! This study utilized data from over 90,000 participants to come to this conclusion. While it echoes similar concepts and findings from previous research (4), the size of this study makes it quite compelling and the findings more conclusive.

What’s the takeaway?

Sleep debt is an important factor to consider in our overall sleep goals. We can’t aim for perfection every night, but the accumulation of sleep debt tends to make us feel worse, and ultimately increases risk factors for adverse health conditions in the long run.

While it’s obviously best to avoid accumulating the sleep debt at all, by taking an intentional approach, we can still work to overcome sleep debt, and ultimately reduce the risk of these conditions. Let me emphasize – it is still better to avoid accumulating sleep debt in the first place! However, some of the negatives can be lessened with ‘catch up sleep.’ It’s not easy, and the results are not immediate. In fact, research suggests only one quarter of us effectively use the weekends to make up for reduced sleep during the week (5). 

Nevertheless, if you keep at it and use Athlytic as your guide, you’ll be able to see the results and reap the rewards for years to come.

Sources and Further Readings:

1. Gallicchio L, Kalesan B. Sleep duration and mortality: a systematic review and meta-analysis. J Sleep Res. 2009;18(2):148–58. 

2. Kitamura S, Katayose Y, Nakazaki K, Motomura Y, Oba K, Katsunuma R, et al. Estimating individual optimal sleep duration and potential sleep debt. Sci Rep. 2016 Oct 24;6(1):35812. 

3. Catching up on sleep on weekends may lower heart disease risk by up to 20% [Internet]. [cited 2024 Sep 23]. Available from: https://www.escardio.org/The-ESC/Press-Office/Press-releases/Catching-up-on-sleep-on-weekends-may-lower-heart-disease-risk-by-up-to-20, https://www.escardio.org/The-ESC/Press-Office/Press-releases/Catching-up-on-sleep-on-weekends-may-lower-heart-disease-risk-by-up-to-20

4. Yoshiike T, Kawamura A, Utsumi T, Matsui K, Kuriyama K. A prospective study of the association of weekend catch-up sleep and sleep duration with mortality in middle-aged adults. Sleep Biol Rhythms. 2023 Oct 1;21(4):409–18. 

5. Leger D, Richard JB, Collin O, Sauvet F, Faraut B. 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 Med. 2020 Oct;74:278–88.