Just because you sleep later than your early rising friends doesn't mean you sleep longer than they do; nor does it make you lazier. And yet, the association between the time of day that a person wakes up and how proactive or driven they are is just one example of the many preconceptions that society upholds regarding sleep and productivity.


But here's the problem: these expectations might actually be working against us.

In his recently published book, Internal time: Chronotypes, Social Jet Lag and Why You're So Tired, German chronobiologist Till Roenneberg provides numerous examples of how social expectations surrounding time may be having a detrimental effect on large sections of the human population. Over on Brain Pickings, Maria Popova walks us through one of Roenneberg's examples, wherein he examines the clash between adolescents' sleep cycles and the starting times of typical school days:

Roenneberg points out that in our culture, there is a great disconnect between teenagers' biological abilities and our social expectations of them, encapsulated in what is known as the disco hypothesis - the notion that if only teens would go to bed earlier, meaning not party until late, they'd be better able to wake up clear-headed and ready for school at the expected time. The data, however, indicate otherwise - adolescents' internal time is shifted so they don't find sleep before the small hours of the night. Here, we brush up against a painfully obtrusive cultural obstacle: School starts early - as early as 7 A.M. in some European countries - and teens are expected to perform well on a schedule not designed with their internal time in mind. As a result, studies have shown that many students show the signs of narcolepsy - a severe sleeping disorder that makes one fall asleep at once when given the chance, immediately entering REM sleep.


In other words: our culture's tendency to associate early rising with an ideal sleep pattern may be clashing with the biological needs of teenagers. On one hand, studies like this are troubling, because they suggest that we're standing in the way of our students' success. At they same time, however, they seem to point to a straightforward solution: simply tailor start-times to better fit the teenagers' biological clocks:

"Teenagers need around eight to ten hours of sleep but get much less during their workweek," writes Roenneberg. "A recent study found that when the starting time of high school is delayed by an hour, the percentage of students who get at least eight hours of sleep per night jumps from 35.7 percent to 50 percent.

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"Adolescent students' attendance rate, their performance, their motivation, even their eating habits all improve significantly if school times are delayed."

Of course, teenagers aren't the only ones who feel the ill effects of a disconnect between biological time and social time. Evidence continues to pile up that the late-night schedules of shift workers clash so violently with their internal biological clocks that they actually increase their risk of obesity, diabetes, and a long list of other nasty health effects. Researchers have linked these adverse effects to discordance between the timekeeping mechanisms within our own bodies (the molecules that control the daily cycle of fat production and storage in your liver, for example) and our odd-hour work schedules.


Researchers who study metabolism call this "circadian misalignment." Roenneberg calls it "social jet lag" (a concept he explains quite succinctly in the video featured here). Whatever you call it, a growing body of evidence suggests that the disconnect between our internal clocks and societal clocks could be informing aspects of our daily lives ranging from metabolic disorders, to suicide rates, to alcohol consumption, to why older men marry younger women.


You can read more about Roenneberg's book, Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired, and his research over on Brain Pickings.