Do you often start your day feeling tired? Do you ever fall asleep at work? Do you sometimes just feel out of it -- as if your brain is still asleep, even though your body is awake?If you answered "yes" to any of these questions, you might be suffering from what researchers call "social jet lag." And help might come from simply changing your work hours.Till Roenneberg is a German chronobiologist. "Chono" comes from the Greek root word "chronos" and means "time." So, a chronobiologist is a scientist that studies the states of being awake and being asleep.Mr. Roenneberg says that many people are working at times that don't match their body's natural sleep-wake cycle. This natural cycle is called the circadian rhythm. Mr. Roenneberg says when your work schedule conflicts with your body's inner clock it leads to extreme tiredness, similar to "jet lag"."... meaning your body clock would give you the optimal window for sleeping, let's say between midnight and eight o'clock ((in the morning)) or even later, but your social schedules would like you to fall asleep at ten o'clock and get up at six o'clock with the work times, for example. And that discrepancy is very much like a jet lag situation."With jet lag, people feel extremely tired when they travel by air far distances. They end up in a place where the sleep-wake cycle is different from their own.Till Roenneberg led researchers in a study at Ludwig-Maximilian University in Munich, Germany. They studied "social jet lag" among workers at a steel company in Europe.Factory workers were given work times that matched their natural sleeping habits. Supervisors did not force the so-called "night owls," people who like to stay awake at night, to get up early for work. On the other hand, supervisors also did not force early risers, sometimes called "larks," to work late.Changing the schedules of the workers to fit their lifestyle improved their sense of wellbeing, says scientist Mr. Roenneberg."They sleep up to almost an hour longer on work days and therefore much shorter on their free days. Normally, people have to catch up on their sleep loss on their work-free days. And we have shortened sleep on work-free days and lengthened the sleep on work days."In other words, with the extra hour of sleep, workers reported feeling more rested. They also reported having small improvements in their general wellbeing.However, Mr. Roenneberg says, the night owls did not report the same level of improvement. This suggests that nighttime work is hard on everyone.He adds that employees who wake up after better rest are more productive."We still have to convince the employers that this is of financial benefits for them; and of course the workers, too, that it is of health benefits for them too. And so this just the beginning and that's why we went into a large industry to do this experiment to show that it works."The study was published in the journal Current Biology.Till Roenneberg and his team now plan to experiment with mice to investigate a suspected link between "social jet lag" and health problems, including obesity.更多听力请访问51voa.com