You may have heard of the term ‘sleep debt’. Is it a real thing? How can you use sleep debt to help both get to sleep and stay asleep? Learning how to use sleep debt to your advantage can be a helpful tool in managing your sleep.
What is sleep debt?
“Sleep debt” is the accumulated drive for sleep that gradually builds up when humans are awake. It is an internal body process as part of the sleep homeostatic system and is sometimes called ‘Process S’. It is considered a sleep deficit since it measures the difference between how much sleep you need and how much you actually get.
Process S refers to the buildup of sleep pressure. This pressure to sleep builds up wakefulness and then decreases as we sleep. For most people, being awake for 16 hours will build up enough sleep pressure to fall asleep and stay asleep for around 8 hours. Process S is homeostatic, which means we can only go without sleep before our sleep pressure builds up high enough that we can’t maintain wakefulness.
We’re all aware of the feeling of being increasingly sleepy the longer we are awake. Eventually, there will come a point where we can’t hold off sleep any longer and find ourselves falling asleep uncontrollably. However, there is another process that interacts with sleep debt – your body clock. So whilst we may pull an all-nighter and accumulate a lot of sleep debt, we are not as sleepy the next day as we are in the early hours of the morning before we would usually wake up. This is the effect of the body clock, also called ‘Process C’, which can either increase or decrease how strongly we feel the impact of sleep debt.
Process C is the answer to how our body knows our sleeping time. This process is responsible for the timing of sleep. Process C refers to our circadian rhythm, a 24-hour cycle that oscillates like a sine wave and might be affected by body temperature, hormone production, and digestion.
The interaction between sleep debt (process S) and our body clock (process C) is discussed in this video produced by Hailey Meaklim.
How do we accumulate sleep debt?
Accumulating sleep debt doesn’t always mean that we feel tired. Sleep debt most often occurs when insufficient hours of sleep are obtained to meet your individual sleep needs. This may occur due to sleep restriction, in which too few hours are spent sleeping.
For example, if your body needs 8 hours of sleep per night but only gets 6, you have accumulated two hours of sleep debt. Since sleep debt is cumulative, sleeping 30 to 60 minutes less than usual for a few days can quickly add up. Not getting adequate sleep over a series of days causes sleep debt to build day by day progressively.
How do we reduce sleep debt?
Taking a nap is usually the first solution we think of when we’re underslept. A short 10 to 20-minute nap may help you feel more refreshed during the day. A mid-afternoon nap can also help us increase working memory, learning, and mental acuity for a few hours.
Ideally ensuring we have enough time and opportunity for sleep each night ensures we don’t accumulate sleep debt over time. But if you find your sleep debt has built up, allowing extra time for sleep each night can pretty quickly get you back on track.
Although it isn’t ideal, if there isn’t an opportunity to catch up on sleep through the week, you can plan to have additional sleep on days off or the weekend. Unfortunately, it’s not clear if sleeping in actually compensates for sleep debt or if it simply represents a return to our standard sleep patterns. One study found that sleeping on weekends doesn’t reverse the metabolic dysregulation and potential weight gain associated with regular sleep loss.
Using sleep debt to help manage sleep
On the other hand, sleep debt can be a beneficial tool to help manage your sleep. People who are not sleeping well spend more time in bed, either going to bed earlier or staying in bed later. This leads to less time during the day being awake doing things and building up sleep debt. If we don’t have enough sleep debt, it can be hard to get to sleep or get back to sleep when we wake up during the night.
This is the principle of sleep restriction, a really powerful technique for helping to get sleep back on track. Sleep restriction is a very powerful tool to help reduce insomnia, making it easier to get to sleep or get back to sleep during the night. Recent research done by University of Auckland researchers, showed improved sleep quality reduced symptoms of insomnia, shorter time taken to get to sleep (sleep latency) and less time awake during the night (wake after sleep onset – WASO).
What if I’m still having trouble?
If you’ve looked at your pattern of behaviour around sleep and tried increasing your sleep debt using sleep restriction but are still having trouble, talk to your GP or healthcare professional. They will assess your overall health, look for other factors that might be impacting your sleep and recommend additional treatments depending on your circumstances. They may refer you to a sleep specialist if they are concerned that you need more specialised treatment.
Related links and posts:
- Video on interaction between process S and process C
- Sleep restriction
- Cognitive behaviour therapy (CBT) for insomnia
- Podcast on CBT for insomnia including interview on sleep restriction
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