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Sleep Debt = Hours of sleep you need per night – Hours of sleep you actually get
During a busy week recently, I averaged 5-6 hours of sleep per night, and planned on getting my eight hours of sleep on the weekend nights. After getting less-than-adequate sleep for 5 consecutive nights, I noticed it had started to take a toll on me. By Friday, I felt like I had pulled an all-nighter the night before.
When the weekend came, I slept in and got 10 hours of sleep per night to partially make up for the sleep I had missed over the week. I’m sure many of you have experienced a similar scenario. I had accumulated sleep debt during the week, and I paid it back over the weekend.
Your Sleep Bank Account
The whole idea of sleep debt comes from the analogy of having a sleep bank account, where you can make sleep deposits and debits. This analogy is not perfect, and can be a bit confusing. Here are some caveats to the sleep bank account:
- Current research suggests your maximum sleep debt is 20 hours
- You cannot “sleep ahead” and build up your sleep bank account
- You can only pay back sleep debt in increments of 1-2 hours; If you are 10 hours in sleep debt, don’t expect to pay it all back at once
Losing one hour of sleep per night over a week is equivalent to pulling one all-nighter- here’s an example to explain why:
Sleep Debt Comparison Example: Sarah and Ashley
Sarah and Ashley both need eight hours of sleep per night. Sarah gets 6 hours of sleep on week nights, and 8 hours of sleep on the weekend. Ashley gets 8 hours of sleep per night, except for Thursday night, when she pulls an all-nighter:
At the end of the week, Sarah has 10 hours of sleep debt (56 – 46); Ashley has 8 hours of sleep debt (56 – 48). So both women have similar levels of sleep debt, even though one accumulated the debt all over Thursday night. Their similar levels of sleep debt will give them similar negative symptoms of sleep deprivation:
- Daytime drowsiness
- Mood shifts, including depression, increased irritability, and loss of sense of humor
- Stress, anxiety, and loss of coping skills
- Lack of interest in socializing with others
- Weight gain
- Reduced immunity to disease and viral infection
- Feelings of lethargy
- Reduced productivity
Why not just sleep in on weekends to pay back sleep debt?
You cannot make up for large sleep losses during the week by sleeping in on weekends any more than you can make up for lack of regular exercise and overeating during the week by working out and dieting only on the weekends.
-James B. Maas, Power Sleep
You can make payments of an extra couple of hours of sleep on Saturday and Sunday to pay back part of your sleep debt. But you aren’t likely to be able to pay more than 2 hours at a time. You still have debt left, and this doesn’t get to the root of the problem- you still face symptoms of sleep deprivation over the course of your week.
Calculating the Hours of sleep you need per night
Each individual has different sleep needs- some need 9-10 hours of sleep per night to perform at their best. Others function perfectly at 5-6 hours of sleep per night. Thomas Edison slept three or four hours at night, and regarded sleep as a waste of time. Albert Einstein needed 10 hours of sleep per night to function well.
Note: Before calculating your hours of sleep needed, be sure to review my previous post on do’s and dont’s for better sleep. Caffeine, alcohol, your diet, and exercise habits all play a role in sleep quality.
The Easy (Less Accurate) Way to Calculate Your Nightly Sleep Needs
If you feel drowsy during the day, you probably didn’t get enough sleep the night before. Try going to bed earlier and see if you feel alert the next day. If you do, this is your nightly sleep need.
The Accurate Way to Calculate Your Nightly Sleep Needs
- Select a bedtime at least eight hours before you need to wake up
- Maintain this time for a week and keep track of the time that you wake up
- If you feel drowsy or don’t get up easily to your alarm, go to bed thirty minutes earlier than usual
- If you feel alert, try to cut back fifteen minutes and see if you still feel alert to confirm if this is your correct number of sleep hours
Calculating your Sleep Debt
Take your nightly sleep need, and subtract it by the amount of sleep you actually got. The number that remains is your sleep debt:
Sleep debt = Hours of sleep you need per night – Hours of sleep you actually get
Paying back sleep debt
You cannot replace lost sleep all at once. If you lose two nights of sleep you will not sleep for fourteen or sixteen additional hours on the third night. When you sleep longer to catch up, try to do so by going to bed earlier than usual. Otherwise your normal waking time will be shifted. This is likely to make it difficult to get to sleep at the usual time the following night.
-James B. Maas, Power Sleep
As Dr. Maas mentions in Power Sleep, you should pay back your sleep debt by going to bed earlier than usual. This way, you can maintain your normal waking time. You can also use a nap to help you pay back your sleep debt. But make sure you take your nap in the early afternoon, as late-afternoon napping will shift your biological clock, making getting up in the morning a struggle.
Avoid accumulating new sleep debt
After factoring how much sleep you need, and repaying your sleep debt, factor it into your daily schedule. Create a daily ritual (see my creating daily habits post) of going to bed and getting up at the same time, each day of the week. This will ensure you do not accumulate new sleep debt.
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