Go ahead and reset your alarm.
You’ve heard the stories.
Apple CEO Tim Cook wakes up at 3:45 every morning. Both Vogue’s Anna Wintour and Twitter’s Jack Dorsey have alarms that go off before 6 a.m. Frank Lloyd Wright, Margaret Thatcher, and Ernest Hemingway never slept through a sunrise.
Maybe that’s all true. But showing the world our best, most productive selves may actually have very little to do with the time we wake up — or when we go to bed. According to a growing body of research, what really counts is doing both consistently. That means every. Single. Day.
A study from Brigham and Women’s Hospital tracked the sleep patterns of 61 full-time students at Harvard College for 30 days, and compared their academic performance. The students all got about the same amount of sleep, but those with irregular sleep schedules — participants who went to bed and woke up at different times throughout the week — fared worse than those who stuck to the same sleep routine.
“Our results indicate that going to sleep and waking up at approximately the same time is as important as the number of hours one sleeps,” lead author Andrew J.K. Phillips, a biophysicist at Brigham and Women’s, says in a statement.
The findings, a footnote to every “early bird gets the worm” story, are the latest in a string of research claiming that a good night’s sleep isn’t just getting seven to nine hours of shut-eye — it’s also about getting the same seven to nine hours every night.
This spring, researchers at Baylor University ran a similar case study on the nighttime routines of young adults. Interior design students wore wristbands that measured their sleep, and took part in tests that measured their cognitive abilities. The more variable their sleep schedule was, the worse they performed throughout the week, researchers found.
Here’s how it works: Our circadian rhythm, or “body clock,” regulates melatonin, the hormone that helps us fall and stay sleep. A fluctuating sleep pattern screws up that body clock — which, in turn, screws us up too.
“Sleep is a part of a larger system of biological rhythms that regulate everything from brain function to muscle repair,” says Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona. “The more variable your sleep schedule, the more these systems are not working optimally together.”
So what should those hours be? The answer, it turns out, is up to you. Everyone has their own “biological night” — a personalized time frame when the body wants to go to bed, Grandner says. This varies from person to person, and can change over an individual’s lifetime (that’s why older adults tend to go to sleep and wake up earlier, and adolescents tend to do the opposite).
People who ignore their personal “night” face serious consequences. In a September article about chronobiology — a growing field devoted to our so-called “inner biological clocks” — Popular Science documented the collective health of graveyard-shift employees, who often wind up adjusting their sleep patterns to accommodate varying work schedules. People who work the night shift, even if it’s just once a week, suffer from focus and exhaustion issues, according to researchers quoted in the piece.
And that’s not all.
Consistency is key, says Michael Breus, a clinical psychologist and sleep specialist. So if “early to bed, early to rise” feels more like a punishment than a personal philosophy, committing to a regular sleep schedule is a smarter bet than trying to fake it as a morning person.
“If you go to bed at the same time and wake up at the same time (even on the weekends), your rhythm will stay in sync,” he says.
This story originally appeared on Money.com.