Having Trouble Sleeping in? This Study May Explain Why

There’s no greater feeling than not setting an alarm for Saturday morning. You can sleep in for as long as you want and wake up feeling well-rested—until you look at your phone and realize you woke up at 6:00 a.m. and you can’t fall back asleep no matter how badly you want to. If this has ever happened to you, you’re not alone. And now, we may know what causes this bodily quirk.

According to a study conducted by researchers at the University of California, San Francisco, one in 300 people are “extreme early birds” whose bodies thrive on going to bed very early—think around 8 p.m.—and waking up very early—around 4 a.m.

If you have the condition, which the researchers call “advanced sleep phase,” it means your body’s circadian rhythm operates earlier than most people’s. When it’s time for bed, your body releases the sleep hormone melatonin and your body temperature shifts. And if you’re an extreme early bird, it happens earlier than normal.

“While most people struggle with getting out of bed at 4 or 5 a.m., people with advanced sleep phase wake up naturally at this time, rested and ready to take on the day,” says the study’s senior author Louis Ptacek, MD, professor of neurology at the UCSF School of Medicine, ScienceDaily reports. “These extreme early birds tend to function well in the daytime but may have trouble staying awake for social commitments in the evening.”

Advanced sleep phase was once considered to be extremely rare. But now, these findings show it may be more common than previously thought. The reason behind it? Genetics. The study followed a group of people deemed to be “advanced sleepers” for nine years. Interestingly, all of them said they had at least one first-degree relative who followed the same extreme early bird sleep-wake schedule they did. Researchers determined that this advanced sleep phase is likely familial.

If you’re regularly asleep by 8 p.m. and up at 4 a.m., just know that you’re not the only one. But you may have already known that, since you likely have a family member who is the same way.