"The more social jetlag you have, the more likely it is that you are a smoker; the more alcohol you drink; the higher your caffeine consumption -- you're slightly more depressed than the rest of the population," he says.
In his latest study, which is published in Current Biology, Roenneberg and his colleagues mined data from a large database, eventually gathering information on 65,000 people. He measured the average midpoint of a person's sleep on weekdays compared to weekends. The difference in those numbers gave him their social jet lag. For instance, Roenneberg's research shows that most of the population would naturally like to sleep between 1 a.m. and 9 a.m. These are the people most likely to experience social jet lag during the week, when they have to get up early for work. So, a person who goes to bed at 1 a.m. and gets up at 6 a.m. during the work week, for example, would have 1 1/2 hours of social jet lag, based on Roenneberg's formula.
He found that the more social jet lag a person experienced, the more likely they were to be overweight or obese.
Social Jet Lag and Weight Gain
So how could sleep that is out of sync with the body's clock potentially lead to weight gain?
One way, says Orfeu Buxton, PhD, an assistant professor of sleep medicine at Harvard Medical School, is that sleeping against the biological clock is closely linked to not getting enough sleep.
"To the extent that sleep duration and timing are up to us, our physiology is tuned to help us get enough," he says in an email to WebMD. "If our sleep is not up to us, we're much less likely to get enough to stay healthy. And whatever it is limiting our sleep may also limit time for exercise or preparing healthy meals."