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Dr. Constance Fung considers herself to be a night owl but has always wanted to be an early bird.
“I always envision myself getting up really early and exercising and having everything done before the sun gets up,” says Fung, a sleep medicine physician with training in geriatrics and a professor of medicine at the University of California, Los Angeles. “But then usually it doesn’t turn out like that.”
Everyone has a natural preference for when they prefer to sleep or be awake, known as chronotype, Fung says.
Your chronotype reflects how your circadian rhythm, or your body’s 24-hour internal clock, is timed. The clock regulates sleep and other processes, like digestion and hormone release. Light influences circadian rhythm, but your chronotype — which also determines when you’re at your peak alertness and energy level — might not align with the sunrise and sunset.
Some people’s internal clocks are naturally shorter, while others’ are longer, Fung says.
Those with shorter circadian rhythms tend to be early birds, or morning larks — they naturally fall asleep and wake up earlier and feel most active and alert earlier in the day, says Dr. David Kuhlmann, a sleep medicine physician and spokesperson for the American Academy of Sleep Medicine, who’s an early riser.
People with longer circadian rhythms tend to be night owls, as they prefer to fall asleep and wake up later, he says, and they’re at their peak in the late evening or at night.
Most people are considered intermediate, not really falling into either extreme. Where you fall on the chronotype spectrum is influenced by several factors, including genetics and lifestyle, Fung says.
Is one type better than the other? Here’s what sleep experts want you to know.
What makes you an early bird or a night owl?
Genetics is the strongest predictor, says Dr. Brienne Miner, an assistant professor at the Yale School of Medicine who specializes in geriatric and sleep medicine. Genes regulate your sleep-wake cycles by dictating when your brain releases the hormone melatonin, which controls circadian rhythm.
“So a lot of people are sort of born that way,” says Miner, who’s a morning person.
Lifestyle factors play a role too. For instance, working unconventional hours, such as shift work, can disrupt natural circadian rhythms, says Dr. Joseph Giaimo, a sleep medicine physician and past president of the American Osteopathic Association. He considers himself a “hummingbird,” someone who floats between being an early bird and a night owl.
Age can also lead to a shift in chronotype, says Dr. Jamie Zeitzer, a professor of psychiatry and behavioral sciences (sleep medicine) at Stanford Medicine. In adolescence, people often become night owls but begin going to sleep and waking up earlier as they get older.
Scientists aren’t exactly sure why this happens, Zeitzer says, but it’s likely a combination of biological changes and behavioral factors. And your body adapts to these changes, Giaimo says.
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