Are you an 'extreme early bird'?

Early to bed and early to rise? In its extreme form, this tendency is more common than previously believed, according to a new study.

Going to sleep at 8 p.m. and waking up as early as 4 a.m. is called advanced sleep phase. It was believed to be rare, but this study concluded that it may affect at least one in 300 adults.

Premature melatonin release

In advanced sleep phase, your body clock (circadian rhythm) is on a schedule hours earlier than most other people's. You have premature release of the sleep hormone melatonin and shift in body temperature.

Advanced sleepers also wake more easily than others and are satisfied with an average of five-to-10 minutes extra sleep on nonwork days, compared with the 30-to-38 minutes more sleep that other people would take advantage of, according to study senior author Dr Louis Ptacek. He's a professor of neurology at the University of California, San Francisco.

Advanced sleep is not the same as early rising that develops with normal ageing, or the waking in the early hours linked to depression.

"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," Ptacek said in a university 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," he added.

Circadian clock genes

In order to determine the prevalence of advanced sleepers, the researchers analysed data from more than 2 400 patients at a sleep disorder clinic. Of those, 0.03% were determined to be advanced sleepers. This is a conservative estimate, the study authors explained, because it did not include patients who didn't want to participate in the study or advanced sleepers who had no need to attend a sleep clinic.

The researchers also said that all of the advanced sleepers in the study reported at least one close relative with the same early sleep-wake schedule.

"We hope the results of this study will not only raise awareness of advanced sleep phase and familial advanced sleep phase, but also help identify the circadian clock genes and any medical conditions that they may influence," Ptacek said.

The report was published in the journal Sleep.

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