May 10, 2012 -- People who have different sleep patterns on the weekends than they do during the work week may experience "social jet lag," and a new study shows this shift in sleep schedule is linked to obesity.
For every hour of social jet lag, the risk of being overweight or obese rises about 33%, says researcher Till Roenneberg, PhD, a professor at the Institute of Medical Psychology at the University of Munich.
Roenneberg, who coined the term, says social jet lag is brought on by the shift in sleep schedule that many people experience on their days off, compared to work days. He estimates that it affects about two-thirds of the population.
It goes like this: You don't have to get up for work so you don't bother setting the alarm. That means you get up an hour or two later than you might during the work week. You may also push your bedtime back so you can go out with friends.
As a result, many people get more sleep on their days off than they do during the week, and they sleep on a slightly different schedule -- a schedule that is closer to their body's natural rhythms.
Roenneberg explains that switching sleep schedules this way feels like changing time zones.
"The behavior looks like if most people on a Friday evening fly from Paris to New York or Los Angeles to Tokyo and on Monday they fly back. Since this looks like almost a travel jet lag situation, we called it social jet lag," he says.
A key difference between travel jet lag and social jet lag, however, is light. When you arrive in a different place, the sun is coming up and setting at a different time, and your body can reset its own clock to match.
With social jet lag, the schedule disruption is chronic because a person stays in the same place.
"They have to live a life almost in a different time zone in comparison to their biological clock," Roenneberg says.
Social Jet Lag and Health
Roenneberg's previous research shows that social jet lag, although not usually as extreme as the sleep disruptions seen in shift workers, can still take a hefty toll on health.