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There Are Actually Four Sleep Schedules, Not Two

It’s 9 a.m. For early birds, also known as larks, it’s the prime time of the day—the moment they feel most energized and alert. Come evening, early birds may start to feel drained or lethargic. They retire at a reasonable hour and wake early—early to bed, early to rise. “Morningness,” as it’s sometimes referred to by researchers, is one of two basic chronotypes, or sleep-wake patterns.

Not altogether surprisingly, “eveningness” is the other. Remember that roommate you had in college? The one who routinely slept through all her morning classes and couldn’t hold a conversation before noon? So-called night owls are known to have difficulty getting out of bed in the morning. Their physical and mental energy levels peak in the mid-afternoon or evening, and they tend to go to bed late and sleep late, too.

These two widely known chronotypes were once thought to apply to everybody. Maybe you identify with one of them. In the very least, you probably know a handful of people who claim they can’t function either early in the morning, or late at night.

But now, a new study out of the Siberian Branch of the Russian Academy of Sciences is challenging the idea that there are only two chronotypes. The study, which appeared in Personality and Individual Differences, posits that there are two further “bird types”—people who feel alert both in the morning and the evening, and people who feel sluggish all day long.

The study asked 130 participants to stay up for a period of 24 hours. Electroencephalographic (EEG) recordings were used to track physiological activity, while participants filled out questionnaires indicating how awake they felt, and what kind of sleep schedule they’d kept in the week leading up to the study.

Twenty-two percent of participants were early birds. Their energy levels were higher at 9 a.m. than 9 p.m. The opposite was true for 44 percent of those involved in the study, who also went to bed later, on average, than the early birds. But together, these larks and night owls accounted for just over half of the total group. The others didn’t seem to fall into either category.

Instead, 19 percent of participants appeared energetic both in the morning and the evening and the remaining 25 percent appeared sleepy both in the morning and the evening. These two groups woke up and went to sleep sometime in between the hours kept by early birds and night owls. Among all groups, the “energetic” group slept the least.

In short, now there’s a sleep-wake pattern that can put even the early birds to shame.

And if you’re someone who consistently feels dozy and tired for no apparent reason, you can stop worrying about being low on magnesium or having a malfunctioning thyroid gland. Blame your chronotype. It won’t change the fact that you feel sleepy, but it will give you a license to complain about it.

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