Aug. 6 (UPI) -- A gene carried by about 1 in 300 causes people to go to sleep around 8 p.m. and wake up as early as 4 a.m., a new study says.
A condition called advanced sleep phase triggers a premature release of the sleep hormone melatonin within the circadian rhythm, the body's internal sleep clock. This is unrelated to what causes seniors and people with depression to wake up early.
These findings were published on Tuesday in the SLEEP.
"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," Louis Ptacek, a researcher at the University of California at San Francisco and study senior author, said in a news release. "These extreme early birds tend to function well in the daytime but may have trouble staying awake for social commitments in the evening."
To examine this condition, the researchers looked at more than 2,400 patients, including 1,748 with symptoms of obstructive sleep apnea, which didn't affect sleep-cycle hours. Of that group, eight people were diagnosed with advanced sleep phase.
"Generally, we find that it's the people with delayed sleep phase -- those night owls that can't sleep until as late as 7 a.m. -- who are more likely to visit a sleep clinic. They have trouble getting up for work and frequently deal with chronic sleep deprivation," said Ptacek.
To qualify as an advanced sleeper, patients had to fall asleep before 8:30 p.m. and rise before 5:30 a.m., and sleep only once a day. This routine had to have started before the patients reached age 30. The patients also couldn't use stimulants or sedatives to influence sleep habits, bright lights to induce early rising, or have a medical condition that affected their ability to sleep.
Advanced sleepers typically only pick up five to 10 minutes of extra sleep on non-work days compared to 30 to 38 minutes for family members without advanced sleep phase.
"We hope the results of this study will not only raise awareness of advanced sleep phase and familial advanced sleep phase," Ptacek said, "but also help identify the circadian clock genes and any medical conditions that they may influence."