“Social Jetlag” Contributing to Global Weight Gain

Here’s another reason to get more sleep — and another new term to describe one of our modern maladies: “social jetlag.” What exactly is social jetlag? It is a syndrome caused by the discrepancy between our internal body clock and our social clock. And according to Professor Till Roenneberg, Ph.D. at the University of Munich's Institute of Medical Psychology in Germany, that gap between how much sleep we need and how much we’re actually getting is contributing to our global weight gain and the growing worldwide obesity epidemic.

Each of us has a physiological clock, and that internal clock — also known as our circadian rhythm — is regulated by daylight and darkness to prompt us to go to sleep or wake up. We also have a social clock of things that make up our daily lives, such as our work schedules and social calendars. The problem is, in our modern society of too-late work hours and too much time in front of computer screens, we are listening to our social clocks more than our physiological clocks, causing a greater sleep gap known as social jetlag. As a person’s circadian rhythm gets more out of whack, their physiological clock gets set later and later, keeping them awake into the night, and feeling chronically tired during the day.

Professor Roenneberg and his fellow researchers in Munich discovered the negative effects of social jetlag after compiling and studying the sleep habits of more than 65,000 adults over the past 10 years. Roenneberg and his team recorded sleep times and other data of the participants, such as height and weight, and started to draw conclusions.

The results of the study — which you can read in the May 10 issue of Current Biology — showed that people with different weekday and weekend sleep schedules—i.e., those with more social jetlag — were three times more likely to be overweight. That is a significant increase worth repeating: Three times more likely to be overweight!  Furthermore, the body mass index (BMI) of the overweight participants tended to increase as the gap between their weekday and weekend sleep clocks widened.

Two-thirds of participants reported at least one hour's difference in their average weekday and weekend sleep schedules, and more than 10 percent reported three-plus hours difference between their weekday and weekend sleep schedules. Roenneberg and his colleagues also found that people who are chronically sleep-deprived are also more likely to smoke and drink more alcohol and caffeine.

The results of the study are similar to those of previous studies linking a higher body mass index and even diabetes to the irregular sleep schedules and sleep deprivation of shift workers. But I applaud the efforts of Roenneberg and his team for their work in particular, because they are bringing a public awareness of a growing syndrome that is affecting many people worldwide — not just shift workers or those with irregular work schedules.

So, why does social jetlag cause weight gain? One of the theories is that late hours encourage irregular meal times and late-night eating, when the body has more difficulty digesting and metabolizing food. That translates into body fat. Another is that chronically tired people are less likely to exercise and more likely to smoke and drink, further contributing to weight gain.

Whatever the causes, it is in all our personal best interests to become more aware of our own physiological clocks and get more restful sleep. Doing so can help us all maintain a healthy body weight, avoid many health problems, feel better and live happier, more productive lives. In the words of Professor Roenneberg, “Good sleep and enough sleep is not a waste of time but a guarantee for better work performance and more fun with friends and family during off-work times.” Knowledge of the study and an increased awareness of the effects of social jetlag can also have positive effects on the economy and education: Companies can make more informed decisions about employees’ work schedules and schools can make more educated decisions about school hours.

So, now that you have this new knowledge about social jetlag, your physiological and social clocks and how a gap between your weekday and weekend sleep schedules can contribute to your weight gain, what are you going to do about it? I present you with a personal challenge that will only help you feel better. I challenge you to get more sleep. Turn off the TV and computer and go to bed earlier. Forego that invitation for a late-night dinner. Spend more time outdoors, and if you’re stuck in an office all day, try to sit near a window. I promise you, you’ll feel less social jetlag.

To read Professor Roenneberg and his team’s full report entitled, “Social Jetlag and Obesity,” published in the May 10 issue of Current Biology.