In mid-May, Carolina Panthers running back and unbreakable bowling ball in a football uniform Christian McCaffrey told GQ that in a perfect world, he’d get at least nine hours of sleep every night. “I can wake up on my own,” he said of hitting that elusive nine-plus hours mark. “I feel great and I’m ready to go.” McCaffrey isn’t alone in this regard, at least among pro athletes: Arizona Cardinals wide receiver Larry Fitzgerald aims for somewhere between nine and 11 hours, while Roger Federer and LeBron James (allegedly) try to get 12 hours of sleep a night.
The consensus view, passed down over the decades via public-service announcement infographics, is that adults should get somewhere between seven and eight hours of shut-eye. But by snoozing a few extra hours, are the world’s tip-top athletes—whose jobs require them to stay in outrageously good shape—on to something the rest of us aren’t?
According to Adrian Owen, a cognitive neuroscience professor at Western University in Ontario, unless you, too, are one of the world’s tip-top athletes, the answer is probably no. In late 2018, Owen and his associates released their findings from a study in which 10,000 participants from around the world self-reported their typical sleeping patterns, and then took a validated cognitive test. (You can sign up to take the test yourself here, if you are so inclined.) Unsurprisingly, the researchers found that regularly getting less than seven hours of sleep negatively affected the cognitive performance of participants. But the study’s results also indicated that too much sleep—more than eight hours—was equally detrimental.
“In the past, the general idea was that more sleep is good, but at least try to get seven or eight hours,” Owen says. “Now, we’ve seen a slight change from that to show that it’s an inverted, U-shaped curve. You need to hit the sweet spot.”
Why? Oversleeping likely causes a form of grogginess called sleep inertia, which depends in part on which part of the sleep cycle you’re in when you wake up. This condition can interfere with your reasoning and decision-making processes. “Most people can appreciate the idea that you don’t want to make a life-changing decision three minutes after you wake up,” Owen explains. And even simple, seemingly inconsequential choices—what to wear, what to eat, whether to cycle or drive to work—impose a cognitive load on an overtaxed brain. Owen says sleeping longer may prolong this critical period of sleep inertia. "I would certainly say if you’ve gotten too much sleep, hold off on any major decisions until the following day," he says.
Don't fret too hard, though; there is some good news about managing the risks associated with oversleeping. First, the high-level conclusions from a population-based study do not apply to everyone. You’re almost certainly not imagining things if you’ve spent most of your life feeling your freshest after more than eight hours of sleep. Some people do benefit from doing their best koala impressions each night—especially professional athletes. “There is good evidence that people who work out a lot and expend a lot of energy during the day need more sleep,” Owen says.
Second, it’s remarkably easy to get back on track if oversleeping has left you with a foggy brain. A single night of the optimum amount of sleep, Owen says—something between seven and eight hours—is all it takes to reboot your system. And in the coming months, he and his associates plan to conduct additional studies on how factors like socioeconomic status and lifestyle choices affect what constitutes the “right” amount of sleep.
But in the meantime, if you’ve made it this far in life without feeling the need to embark on a period of mini-hibernation each night, you don’t need to start doing so now—unless, of course, you're still holding out hope for a Christian McCaffrey–esque NFL career.