You’ve spent Monday through Friday running on five hours of sleep, working late nights and waking up early just to do it all over again. On Saturday, you get 12 glorious hours of shut-eye and feel instantly refreshed when you wake up. You’re all caught up on your sleep, right?
Actually, not quite. The idea that a single morning or weekend spent logging extra hours in bed can wipe away a week’s worth of sleep deprivation is one of the most persistent sleep myths out there.
Here’s what sleep experts wish everyone understood about how “catch-up” sleep actually works and why your z’s can’t just be topped off like a gas tank.
Sleep debt explained
Sleep debt is essentially the difference between how much sleep your body needs and how much it gets, according to Kimberly Fenn, professor of cognition and cognitive neuroscience at Michigan State University. Put another way, it is the cumulative amount of lost sleep an individual has experienced.
In general, you should aim to get at least seven hours of sleep each night, and most people need between seven and nine hours of sleep to function well the next day, said Ulysses Magalang, board-certified physician and director of the Sleep Medicine Program at Ohio State University. The ideal amount for you is whatever allows you to wake up feeling rested and like you have enough energy to make it through the day, according to Fenn.
Each night you don’t sleep a sufficient amount, it adds to the “debt,” Fenn explained. For example, if you need eight hours of sleep every night to feel your best and on Sunday night you sleep for only six hours, on Monday, you’ll have a debt of two hours. If this pattern continues all week, then by Saturday, your cumulative amount of sleep debt would be 10 hours.
Short-term side effects of not getting enough shut-eye include tiredness, trouble concentrating, difficulty paying attention, irritability and memory impairment, Magalang said. Long-term sleep deprivation is associated with health issues such as a weakened immune system, high blood pressure, heart disease, stroke, increased inflammation, cognitive impairment and insulin resistance, according to research.
There’s also some evidence tosuggest that people who consistently get fewer than six hours of sleep each night have shorter lifespans than those who get more than six hours of sleep each night.
Why catching up on sleep isn’t the best strategy
While you might feel refreshed in the short-term after a morning of sleeping in, changing your bedtime and wake-up time drastically can make you feel even groggier or more fatigued, according to Fenn. “Sleep consistency is important for feeling well rested, and straying too far off course can throw off your internal clock,” she said.
She emphasized that maintaining the same bedtime is especially important. If you go to bed at your normal time but have accumulated sleep debt, you can let yourself sleep an additional hour or so in the morning.
“Typically, due to the strength of the circadian rhythm, unless there are other factors involved — like alcohol or other drugs, or extreme sleep loss — most people won’t sleep more than an hour past their habitual wake time,” Fenn said.
But your health might still be compromised, depending on the severity of your sleep debt, according to Fenn. For instance, a small 2019 study in Current Biology found that a weekend of recovery sleep isn’t a good way to prevent the metabolic damage associated with chronic sleep deprivation.
“We know that sleep deprivation is associated with high blood pressure, but there’s really no definitive study that says if you have developed high blood pressure [due to chronic lack of sleep], and then you lengthen your sleep, your high blood pressure will be reversed,” Magalang added.
Additionally, sleep consistency is just as important for your health as the amount of sleep you get, according to Magalang.Sticking roughly to the same bedtime and wake time daily is essential for aligning your body clock, or circadian rhythm, which moderates everything from hormone levels and metabolism to digestion. One large study found that people with the most irregular sleep schedules were 26 percent more likely to experience a major cardiovascular event, including heart attack and stroke. Another linked irregular sleep to a higher risk of early death compared to those with consistent routines.
What to do instead
The best way to combat the health effects of sleep deprivation, according to both experts, is to do your best to aim for that sweet spot of seven to nine hours of shut-eye each night. Prioritizing sleep isn’t always possible though, Fenn acknowledged.
If you do have a few nights where you can’t get the sleep you need and find yourself craving a sleep-in to make up for it, a 20-minute nap during the day can be an effective way to power through the day and maintain your consistent sleep and wake time, according to Fenn.
“This length is considered optimal because it’s sufficient to increase energy, mood and attention, but is typically not long enough to get into deep sleep,” Fenn said. With lengthier naps, there’s a high probability that you’ll wake up in the midst of deep sleep and experience sleep inertia, which is a state of grogginess and reduced cognitive and neuromuscular function, she said.
“That’s why people say that they awake from a nap more tired than they started,” she said. “Being in a state of sleep debt also increases sleep inertia, so taking a long nap after insufficient sleep is even more problematic.”
Sleep is like any other biological necessity — if you skimp on it here and there, you’ll probably be fine in the long term, Fenn said. Your body is resilient and will find ways to manage and forge ahead. But being sleep-deprived for months on end is going to do some serious damage, she said, which is what you want to try to avoid as best as you can.
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