"Social jet lag" is a problem for most of us, and it's fueling the obesity epidemic, study suggests

It's perfectly normal for a guy to feel tired at the end of a busy day. But gus with low "T" feel completely depleted. These guys complain of being more tired than they think they ought to be. "My tank is empty," is how some guys put it. iStockPhoto

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(CBS News) Do you battle with your alarm clock come Monday morning? You may have what researchers are calling "social jet lag" and according to a new study, lots of us have it and it may be fueling the obesity epidemic.

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According to the study, published online in the May 10 issue of Current Biology, social jet lag is a syndrome caused by the mismatch between the body's biological clock and our actual sleep schedules.

Dr. Till Roenneberg, a professor of chronobiology (the study of biological rhythm cycles) at the University of Munich, explains that each of us has a biological clock, but they're not the type we can set like watches. Our clocks are "entrained" by daytime and nighttime and provide the optimal window for when people should sleep.

But in modern society, he says, people listen to their internal clocks "less and less due to the increasing discrepancy between what the body clock tells us and what the boss tells us."

He told WebMD that he estimates two-thirds of the population experiences social jet lag. He coined the term because switching sleep schedules is similar to switching 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," Roenneberg told WebMD. "Since this looks like almost a travel jet lag situation, we called it social jet lag."

For the study, Roenneberg and his team analyzed data from a database of 65,000 people that they have been compiling for more than 10 years, which included information on height, weight and sleeping habits. Their analysis found people with more severe cases of social jet lag were much more likely to be obese. For every hour of social jet lag, the risk of being obese or overweight rose by 33 percent. What's more, people who chronically experience social jet lag are more likely to engage in unhealthy habits like drinking alcohol and caffeine, or smoking.

The researchers say their findings should impact Daylight Savings Time and when work and school starts. They recommend people spend more time outdoors in daylight or sit by a window, or else their body clock keeps getting set later and later, keeping them up and making them tired the next day.

"Waking up with an alarm clock is a relatively new facet of our lives," Roenneberg said in a news release. "It simply means that we haven't slept enough and this is the reason why we are chronically tired. 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."

Previous studieshave shown people who are shift-workers, such as transportation workers, are at a higher risk for obesity and diabetes because of their varying sleep schedules that constantly throw off their bodies' internal clocks.

"We've known for a while that shift workers are associated with increased health risks, and shift workers have extreme variability in their sleep timing between workdays and non-workdays," Dr. Kristen Knutson, a sleep researcher at the University of Chicago in Illinois who was not involved with the new study, told Science Magazine. "This paper suggests it's not just the extreme cases of irregular bed times, but even a more modest difference between weekends and weekdays of an hour or two seems to be associated with health outcomes like obesity."

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