Science proves you’re not losing your mojo—you’re tired.

By Maggie Seaver
Updated June 21, 2019

Have you ever lost an hour or two of your normal sleep cycle and thought, Whatever, I’ll just chug some coffee, power through, and catch up on sleep tomorrow night? While that sleep you lost won’t kill you tomorrow, it certainly won’t help your performance at work the next day. And if you’re wondering why your work output and ability to focus isn’t quite up to snuff, even when you thought you caught enough Z's, even the smallest bit of sleep deprivation could have something to do with it.

In a scientific study recently published in the Sleep Health Journal, researchers at the University of South Florida and Penn State University sought to answer the question: Is nightly sleep really associated with next-day cognitive interference—and vice versa? In other words, does how much (or how little) sleep you get affect energy and concentration the following day?

In short, the answer is yes. Over eight straight days, study participants recorded both their sleep behaviors (“bedtimes, wake times, sleep duration, sleep quality, and sleep latency") and how often they experienced of "off-task" or "distracting thoughts" the following day on a scale of zero, (never) to four (very often).

According to the study abstract’s results:

"[O]n days following earlier wake times, shorter sleep duration, or poorer sleep quality, participants reported more cognitive interference than usual. That is, waking 19 minutes earlier and sleeping 16 minutes less were associated with one additional point on the cognitive interference scale the next day."

Basically, losing just 16 to 19 minutes of sleep can lead to a dip in focus and productivity, particularly on work days (the study found the correlation between nightly sleep duration/quality and cognitive interference to be much less notable on non-work days—surprise, surprise). If 15 minutes less sleep can make a dent in your alertness and concentration, imagine what losing a few hours can do. (That’s why you really do need to hit the sheets for 7 to 10 hours a night.)

On your average work day, you may be able to get away with a slightly subpar performance and a few extra yawns, but think twice before staying up late or waking up too early before a big presentation or another important work day. (Can’t sleep? Try this counterintuitive trick to help.)