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“Sleep debt” is a term used to describe cumulative sleep loss resulting from ongoing sleep restriction. If you regularly get less sleep than you need, your accumulated sleep debt will grow larger over time. Some say this looming sleep debt makes you tired, grumpy, and prone to accidents and illness.
Experts disagree on the nature of a sleep debt. Some experts, most notably Jim Horne of Loughborough University, say that sleep needs naturally fluctuate with seasonal and social changes. For example, those living in Northern climates without much winter daylight may sleep for many hours during darker months, and naturally shift to sleeping less in the summer, when daylight peaks. And some studies show that social factors like boredom or isolation can increase the drive for sleep. So simply feeling tired or sleeping more doesn’t necessarily indicate that you have a sleep debt, he argues.
Horne says these naturally occurring shifts in sleep cycles don’t indicate that people are incurring or repaying accumulated lost sleep, and may suggest that our bodies’ needs for sleep are more flexible than some assume.
However, many other experts believe that chronic, long-term sleep deprivation is a public health problem with dire economic and social consequences. Research shows that accumulated sleep loss negatively impacts mood and cognitive performance.
In addition to these deficits in mental health and performance, ongoing sleep deprivation is linked to an increase risk for cardiovascular and metabolic illness, driving accidents, and fatigue. Sleep debt has been shown to cause death in lab studies on animals, and rarely, people die from lack of sleep.
What’s your personal sleep debt? Start with the amount of sleep you need to feel rested and alert. If you need 8 hours of sleep each night but only get 7 hours on average, you accumulate a sleep debt of 7 hours each week. Over the course of a year, you’ve lost 364 total hours of sleep, equivalent to nearly 7 weeks of sleep.
With the increased awareness of the dangers of sleep deprivation, many night owls and chronic sleep-skippers wonder if they can repay their looming “sleep debt.” The answer is no, for the most part. Once sleep is missed, it’s gone for good.
Sleeping more for a night or two can help restore some of the cognitive decline caused by a large sleep debt. But clearly, it’s not possible to “repay” a sleep debt totaling hundreds of hours.
However, when a sleep-deprived individual slumbers, the body works to “make up” some lost sleep by spending more time in the deeper, more restorative stages of sleep, and less time in lighter-stage sleep. Scientists observe changes to the sleep stages in people who don’t sleep enough, which generally resolve if the person starts sleeping more. But because each sleep stage is vital to our mental and physical wellbeing, it’s vital to allow enough time for the body to move through all stages of sleep, and not chronically deprive yourself of the rest you need.
The best way to stay out of sleep debt? First, stop adding to your sleep debt by making a real effort to get adequate sleep each night. Determine the amount of sleep you need to feel well-rested, and create a schedule that allows enough time for sleep. A sleep journal can help track your sleep patterns to help you see how much you’re sleeping overall.
Once you decide how much sleep you need each night, solid sleep hygiene habits will help keep your sleep routine on track:
A short daytime nap can help restore your alertness until you can get more rest at night. The best way to accomplish this is with a brief 15-20 minute nap between 11 a.m. and 3 p.m. Why is a midday nap important? If a nap occurs too early in the day, the body won’t be tired enough to fall asleep, while naps that occur after mid-afternoon can make it harder to fall asleep at night. If you can’t get enough coffee, you’re in luck: A “caffeine nap” could be your ideal midday snooze.