If you're having a case of the Mondays, or reading these through squinting eyes and dreaming of your sweet, sweet pillow, it may be because you slept in this past weekend.
Susanna Jernelöv, a psychologist and sleep researcher at Sweden's Karolinska Institute, recently told local media that sleeping in during the weekend can make you more tired the following week. "It's like giving yourself a bit of jet-lag and jet-lag makes you less bright and perky," she said.
Michael J. Breus, a clinical psychologist, a diplomate of the American Board of Sleep Medicine and a fellow of The American Academy of Sleep Medicine, agrees. He tells Broadly that even sleeping in 30 minutes later on Saturday and Sunday can affect how you feel when you return to school or work Monday. "The classic Monday morning fog has a lot to do with if you stay up late Friday, sleep in Saturday, stay up late Saturday, sleep in Sunday," he says. "Your body is starting to shift to that schedule."
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According to the National Sleep Foundation, sleep is regulated by sleep/wake homeostasis and the circadian biological clock. The sleep/wake homeostasis balances the drive for sleep and wakefulness, while the circadian biological clock is what makes you sleepy or feel awake at different points in the day.
By sleeping in, you delay that biological clock, explains Bradley V. Vaughn, a professor of sleep medicine and epilepsy at the University of North Carolina Chapel Hill School of Medicine. "If you're sleeping in an extra hour or two hours, what's happened over the weekend is your body clock is delayed by two hours," he says. Therefore, it's harder to go to sleep Sunday night, and as a result, you may be pretty sleepy come Monday morning.
But, Vaughn tells Broadly, that tiredness doesn't necessarily stay with you the entire week. As your inner clock gets back on track, the waking up gets easier.
If you're sleeping in an extra hour or two hours, what's happened over the weekend is your body clock is delayed by two hours.
Another caveat is sleep deprivation. "If you are not sleeping enough during the week," Vaughn says, "then paying off some of that sleep debt may actually help a little bit. But the ideal would be going to bed earlier, not getting up later."
Breus suggests getting up at your normal time on the weekends, even if you fell into bed at 3 in the morning after a night of partying. "The wake-up is really what is the anchor of your circadian rhythm," he explains. "Getting light in the morning ... restarts it, if you will, and that's what you're trying to accomplish."
Keeping your internal clock stable ensures your body is working at optimal performance, Vaughn says. A study published in the Journal of Clinical Endocrinology and Metabolism last year suggested that interruptions in a person's natural circadian rhythm could lead to risk factors associated with obesity, diabetes and cardiovascular disease.
So is it possible to catch up on lost sleep? "It doesn't really work that way," Breus says. "Sleep is lot like a baseball game. If the game starts at 8 o'clock and you show up at 9:30, they don't restart the game. And also when the game is over—you staying at the ballpark, you're not going to see anything."