Hamburg - The most difficult time for Ullrich Grubig is in the middle of the night, although that's when there is the least amount of work to do.

While his body wants to sleep, Grubig, a precision mechanic, has to stand at his machine. He must hang on until 5 am when his shift ends. Then he can go home and go to bed. Grubig actually is lucky that the overnight shift ends relatively early.

"When shifts end at 8 am, it's usually too bright by the time you get to bed, and that makes it harder to sleep," said Daniel Hicklin, who works at a sleep clinic in Bad Zurzach, Switzerland that advises people who work irregular hours. Daylight signals the body that it's time for activity, not sleep.

At many companies, employees rotate from morning shift to afternoon shift and then to the overnight shift.

"Today, the recommendation is to change every two to three days," said Ingo Fietze of the German society for sleep medicine and sleep research in Berlin. Then the body can adjust better. Ideal is a change from the morning shift to the afternoon shift and then to the overnight shift and then a day off.

"The overnight shift is especially strenuous," said Fietze. Body temperature drops at night and the urge to sleep increases. "You're much more tired and you make mistakes."

But the early shift also can be difficult to deal with. The earlier it starts, the less sleep you get, said Hicklin. A shift that starts at 4 am means getting up in the middle of the night and driving to work. In order to make it through the shift, you have to get to bed early.

"But often, you're not tired enough to sleep, yet you feel the pressure to fall asleep as quickly as possible," Hicklin said.

A few rules help to survive shift work.

"When I go on overnights, I don't drink coffee at the beginning of the shift," said Grubig. Caffeine remains in the bloodstream for four to seven hours. So, the effects of drinking it at 2 am could still be felt at 7 am and thus not be able to sleep.

People who have difficulty getting to sleep after an overnight shift can put on sunglasses on the drive home.

"Light wakes you up," said Fietze. People who work overnight should go to bed immediately and sleep as long as they can. For people who work the early shift, taking a nap after they get home from work can be sensible to settle down in the evening and fall asleep.

Even if it's difficult, people who work shifts must make sure they get enough sleep.

There are people who just can't come to terms with working various shifts. They have difficulty sleeping, problems with their stomach and intestines and circulation problems.

"One can assume that 20 per cent to 25 per cent of the people who work different shifts have problems sleeping and about 4 per cent must be taken off shift work," said Fietze. A doctor should be consulted when workers are unable to get over their fatigue and if they also have problems sleeping at the weekends. (dpa)