We've been talking recently about sleep. And it's an issue for many of us--some of us are morning people; others, night owls. Why? Some always sleep well. Others, not. Why? Well, maybe it depends on what "chronotype" you are. Huh? True--read on:
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This article appeared in the October 20, 2013 issue of The New York Times Magazine.
If you consider yourself to be a born morning person or an inveterate
night owl, there is new research that supports your desire to wake up
early or stay up late. Each of us has a personal “chronotype,” or unique
circadian rhythm, says Till Roenneberg, a professor of chronobiology at
Ludwig Maximilian University in Munich and one of the world’s experts
on sleep. In broad strokes, these chronotypes are usually characterized
as early, intermediate or late, corresponding to people who voluntarily
go to bed and wake early, at a moderate hour or vampirishly late. If you
are forced to wake up earlier than your body naturally would, you
suffer from what Roenneberg calls “social jet lag.”
People with an early chronotype may do well with a 7 a.m. workday
rising time, but others do not. Sleeping out of sync with your innate
preferences can be detrimental to your health, especially for late
chronotypes, who tend to be the most at odds with typical work
schedules. A study conducted by the National Institutes of Health and
published in March in PLOS ONE
found that obese adults with late chronotypes tended to eat larger
meals, develop more sleep apnea and have higher levels of stress
hormones and lower levels of HDL, or “good,” cholesterol than obese
people with other chronotypes.
Their chronotype may also have contributed to weight gain in the
first place, Roenneberg says. Research has shown that a single hour of
social jet lag, the mismatch between your chronotype and your schedule,
increases your risk for obesity by about 33 percent. In a study
published in June in Chronobiology International,
late-night chronotypes gained more weight during their freshman years
at college than other new students did, even though college is one of
the best fits for night owls.
The brain can also be affected. Another study in Chronobiology
found that “individuals having a preference for evening hours to carry
out their daily activities are prone to depression,” more than earlier
chronotypes are. In an August study in NeuroImage,
scientists in Germany scanned the brains of young men and found that
white matter, which carries and amplifies signals between neurons, was
less cohesive in certain parts of the brain in late chronotypes than in
the other volunteers. This could make the brains of late chronotypes a
little “less efficient,” says Jessica Rosenberg, a researcher at the
Institute of Neuroscience and Medicine in Jülich, Germany, and an author
of the study, although, she points out, it’s impossible to tell whether
the lack of sleep caused the brain changes or vice versa.
Almost every cell in our bodies is likely to reflect our chronotype. In a study in May in Chronobiology,
scientists typed volunteers using a questionnaire, then examined cells
from their inner cheeks and found that late chronotypes tended to have
activity in genes that contribute to later sleep onset, offering further
evidence that the urge to stay up late or to rise early is not a
lifestyle choice but resides in our DNA.
Few people have the luxury of organizing their lives by their
chronotypes. If you can’t convince your boss that your body clock
requires a later start, consider “getting outside more,” Roenneberg
says. Infusions of sunlight nudge most chronotypes toward an earlier
sleep time. More immediately, look forward to Nov. 3, the end of
daylight saving time. The summertime clock typically disrupts sleep for
all chronotypes, he says. “Everybody sleeps better when it ends.”
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