It’s the sort of buzzwordy phrase that you would expect to hear at a business seminar: social jetlag. But it’s actually a well-studied phenomenon that might explain why you or your night owl friends often feel groggy at your day job. Unlike garden variety jetlag, social jetlag can also wreak long term damage to your health.
Tick tock goes our body clock
Everyone has their own circadian rhythm, or internal body clock. This clock helps dictate how our bodies function during the 24-hour period of any given day, including when and how long we want to sleep. People fall along a spectrum of preferred sleep times, known as chronotypes. Early birds prefer to wake up early and go to bed early, while night owls tend to go to bed late and wake up late.
A person’s circadian rhythm and chronotype is usually most influenced by the natural day/night cycle along with their genetics. But modern life is now filled with things that can make it harder for some of us to stick to our body clock as often as we’d like to, such as school and work on weekdays. This mismatch is then thought to cause social jetlag.
The term was first coined in a 2006 study by scientists Marc Wittmann, Jenny Dinich, Martha Merrow, and Till Roenneberg. They defined it as a discrepancy between our preferred and forced-upon sleep schedules throughout a typical week. A night owl is likely expected to wake up earlier during the school/work week, for instance, and would only catch up on the hours and type of sleep they prefer on the weekend. An early bird, by contrast, is more likely to get the same amount and timing of sleep the whole week. Estimates vary, but as much as two-thirds of working/studying people in industrialized countries might experience social jetlag, losing at least an hour of sleep on weekdays.
Reams of research have found that drastic disruptions to the circadian rhythm, such as having to regularly work night shifts, can harm our long-term health. So-called shift workers are significantly more likely to experience sleep disorders, heart disease, and diabetes. But even the more subtle alterations caused by social jetlag seem to wear people down over time.
The harms of social jetlag
A 2020 study found that night shift workers had higher levels of social jetlag compared to day shift workers, and that both night shift work and social jetlag were associated with a greater risk of obesity, for instance. A similar pattern has been seen in school children, with a 2020 study finding that night owls were more likely to have social jetlag as well as higher rates of obesity and other metabolic alterations. Studies have also found a link between social jetlag and type 2 diabetes, cardiovascular disease, and depression.
Interestingly enough, social jetlag might paradoxically be a sign of better health in some groups of people. A 2023 study of older adults over 60 found that high social jetlag was tied to worse blood sugar and blood pressure control in working people, but associated with better markers of each in retired people. One possible explanation for this paradox is that social jetlag in retired people can represent an intentionally more active social life, which can be healthy in of itself, compared to the forced, more stressful drudgery of work.
Outside of retirees, though, social jetlag appears to be a subtle but serious public health concern given how common it is—one worth tackling with major policy moves, experts have argued. Scientists like chronobiologist Till Roenneberg, one of the originators of the phrase, have highlighted more flexible work schedules, later school start times, and the ending of Daylight Saving Time as some possible ways to reduce social jetlag. You don’t have to be a night owl to see how those kinds of changes would make plenty of people less stressed and a bit more blessed.
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