Social jet lag was described by chronobiologists (those who study the brain’s time-keeping mechanisms) at University of Munich in 2006 as “misalignment of biological and social time.”
That could mean, for example, that when the world is saying it’s time for bed, you’re not tired. When the world is saying it’s time for work, you’re sure you need more sleep. A growing number of experts believe that this phenomenon is real, common, and beyond our control—and that the health consequences are serious.
Among them is Judith Owens, a Harvard faculty neurologist and director of the Center for Pediatric Sleep Disorders at Boston Children’s Hospital. She believes that morning people need to do more to recognize and respect the biology of non-morning people—who may simply not be built to operate on traditional schedules.
This week in the medical journal Pediatrics, Owens and colleagues found that even among people who sleep the same number of hours, there are behavioral, emotional, and cognitive differences between people who are “night owls” and people who are “morning larks.” This is what she and some sleep experts have lately begun calling a person’s chronotype: the idea that people are “programmed” or “wired” to sleep later or earlier in any 24-hour period.
But society does not always abide, insisting that people simply go to sleep earlier, and that as long as you get seven hours of sleep or so, you should be fine.
“If your sleep patterns are misaligned with your internal circadian rhythms,” Owens told me, “then that’s going to have a more important impact on self-regulation than how much sleep you actually get at night.”
In the latest research, her team studied high-school and middle-school students in Fairfax County, in Virginia, where the first bell rang at 7:20 a.m. The researchers compared thousands of students, some who were morning people and some who were night people. The results showed that even when everyone got the same amount of sleep, “self-regulation” was worse among night people.
Self-regulation is a psychological construct that comes up a lot in health research. Its absence has been associated with a host of negative outcomes, like substance abuse and depression. Owens explained to me that there are three types of self-regulation: emotional, cognitive, and behavioral. In each of these domains, a person can have stability and control (or at least a sense of control). All three can be lost or improved throughout life, but they’re largely shaped by our environments and behaviors during younger years.
Her takeaway: “It’s not just how much you sleep, it’s when you sleep.”
The research shows a correlation between chronotype and self-regulation, so which element might be causing the other—if the two are indeed related—can’t be said. But taken together with other research on night people and morning people, chronotypes do seem to have serious implications for health and wellbeing—in that they influence our standing in societies. Mismatches with people and systems around us can influence educational attainment and, thus, financial and social stability. So in a world that tends to reward and praise morning people, Owens is interested in mitigating systems that discriminate against people of the night.
For example, as NPR’s Morning Edition reported on Wednesday on this research, a 17-year-old named Zachary Lane has four alarm clocks and still “regularly gets detention for being tardy.” Even when he does make it to school on time, he’s groggy. “I feel kind of like I’m lagging behind myself,” he said. “I don't feel totally there.”
That sounds like a serious sleep disorder. Four alarm clocks is too many. Owens says that kids like Lane suffer as a result of a system they can’t control. Academic difficulty can set off a cascade of low confidence, further lack of self-regulation, health problems, and on and on. All from something that wasn’t the night child’s fault to begin with.
“These kids simply cannot fall asleep much before 11:00 at night,” she told me. “That’s the way their circadian rhythms are wired. They need eight to 10 hours of sleep. So, you can do the math.”
(I can and did. I asked her how the night teens in her study were getting as much sleep as the morning teens if the school started at 7:20. She said, “We controlled for all these variables.”)
The point, Owens emphasizes is that many kids “are biologically programmed to wake up around 8:00 or 9:00. By that point, they’ve been in school for two hours. That’s where this brings up the issue of school start times.”
In 2014, she was the lead author of a statement by the American Academy of Pediatrics that implored high schools and middle schools to start no earlier than 8:30.
“Part of the reason behind that was to make sure kids get enough sleep,” she told me. “But it was also to align their school schedules with their biological rhythms.”
So these research findings support her mission nicely.
Since that recommendation, many schools have pushed back their start time. She travels the country giving talks about this: “This isn’t just about school performance; it’s about the health of our kids.”
I don’t know which most parents care about most. But this point, why wouldn’t all schools just change their start times?
“Oh!” she said with a gasp. “There are myriad reasons! Honestly, the biggest one is sports. Practice will be delayed. If you’re playing a team from another district with an earlier start time, that gets screwed up. Some teachers have second jobs and need to get out there. And people like the status quo. Change is hard.”
I told Owens I was on the swim team in high school. We had two practices a day, and the first started at 5:30 in the morning. I said I wonder if I would be smarter now if I hadn’t done that.
She withheld judgment. “It’s crazy.”
After Owens completed the research in Virginia, she was involved in getting the school system to change its start time—which is now 8:10. She’s in the process of studying how that change is going.
But what if I’m a parent with a child whose school starts early, I asked her, and this kid seems to be a night child, what can I do besides lobby the school to adapt to my night child?
At this point, she said that chronotypes are at least somewhat malleable, a sort of Hobbesian understanding of our agency in sleep. She recommends keeping kids off screens when bedtime is nearing. She also recommends not letting your teenager sleep in on weekends. (A super easy and fun thing for a parent.) “That has been shown to delay their circadian rhythms even further,” she said, creating social jet lag.
In his book Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired, chronobiologist Till Roenneberg painted a more daunting picture. He posited evolutionary explanations for modern chronotypes, like that morning people had an advantage in agrarian societies. He went on to tie chronotypes to why birth rates vary with time of year, and even why older men often marry younger women.
Even for someone who doesn’t believe in free will, this often starts to feel too deterministic for me. No doubt there are chronotypes, and the construct is useful to consider. But I’m not sure that chronotypes are inescapable. I’m not convinced that going to sleep earlier or later than the people around you is the result of some innate neurological destiny, some ordained truth about your body’s relationship to sunrise and sunset.
When you go to sleep (and when you wake up) relative to the people around you seems to be a result of myriad lifestyle decisions and environmental factors. When New Yorkers move to Hong Kong, for example, they don’t live forever nocturnally. If the effect of daylight is the basis of the cycle, then explain seasonality. Sunset in New York is four hours earlier in December than it is in July, but we still go to sleep around the same time. Seeing one’s chronotype as a complex network of factors, many of which are malleable, seems to me more intellectually valid and more empowering.
There’s also hope in noting that the final element of Owens’s study was this: Students who described themselves as “sleepy” at school but weren’t actually sleep-deprived ended up scoring just as poorly on self-regulation as people who were actually sleep deprived. Writing oneself off as “not a morning person” could be a self-fulfilling prophecy.
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