SIEMENS

Michael Scheuerer doesn't need much coffee when he works the night shift at the Siemens electrical device manufacturing plant in Amberg. That's because Scheuerer, an electrician who ensures the smooth operation of an assembly line as he alternates between three shifts, is what is known as an owl. That's the term chronobiologists use to describe people who like to go to bed late and sleep late in the morning. Such behavior is caused by our circadian rhythms, a timing system inside the body that has evolved over millions of years and is controlled by the suprachiasmatic nucleus, a group of cells the size of a pinhead located deep in the brain. These nerve cells send impulses to other brain regions to regulate body temperature, hormone production, and sleeping intervals.

The speed at which this internal clock ticks is genetically determined, very much in the same manner as the color of our eyes or our hair color. Owls like Scheuerer have quite a big advantage when it comes to working night shifts. “Most of my co-workers have a lot more problems with fatigue at night,” says Scheuerer, who is 59. “They'd prefer to work only early shifts.” The majority of the members of his team apparently belong to the “lark” chronotype—those who like to wake up early.

It's a well-known fact that shift work has a negative effect on the quality of sleep and the ability to concentrate. It also leads to increased nervousness and fatigue. And it has been proven that shift workers are more likely to use alcohol and tobacco, and are more susceptible to illnesses. One possible reason for this has to do with their lack of exposure to the natural daylight and darkness that normally synchronizes the internal clock with external time (see Duplicating Daylight). But what influence does an individual chronotype have—and can new knowledge in this field be used to improve working conditions? A group of researchers led by Prof. Till Roenneberg from the Ludwig-Maximilians University (LMU) in Munich is examining this question with Siemens—the first company in the world to address the issue.

“For many years, chronobiology was a topic exclusively for science,” says Wolfgang Kloke from Siemens Corporate Technology. However, as Kloke points out, it's also extremely important for workplace organization. More than 150,000 Siemens employees are involved in  shift work around the world, and around 17 million people do shift work at companies in Germany. Kloke believes these workers would feel better, have fewer sick days, and work more efficiently if they were assigned shifts in accordance with their chronotype. “Those who sleep well and work in tune with their internal clocks are more productive and make fewer mistakes,” he says.

Determining Chronotypes. Initial research results confirm this assumption, as the study's manager, LMU psychologist Céline Vetter, reports. “We were able to demonstrate a clear relationship between individual chronotypes and reaction times during specific shifts,” she says. The researchers found that larks react more slowly than owls during night shifts. Moreover, larks who work night shifts sleep less the next day and are less relaxed afterwards. “If we know an employee's chronotype, we can predict how long he or she will sleep and what their reactive capability will be like during a specific shift,” Vetter explains.

Vetter spent weeks with colleagues traveling to Siemens factories, where they handed out surveys and conducted psychological and motor ability tests. At Siemens' plant in Cham, about two hours north of Munich, they examined how chronotype affects concentration. They also took a look at motor ability responses at the company's Berlin electric motor plant. About 180 volunteers took part in the tests. “The first thing we did was determine the chronotypes of the test subjects,” says Vetter. This was done with the help of surveys in the case of individuals who only worked days. The parameter measured was sleeping behavior on days off—the only time when people generally sleep in line with their internal clock. “This doesn't work with shift workers, however, because on their days off they still may be feeling the effects of the last shift, and may have to catch up on their sleep,” says Vetter.

The LMU researchers therefore developed a correction formula for the five-minute questionnaires that normally allow them to determine the chronotype of a shift worker. To verify the correction, the researchers asked subjects to wear an activity meter for the duration of the study This device, which is worn on the wrist, registers body movement, thereby providing a measure of the subject's activity. The scientists also collected data on body temperature and sleep-waking behavior. “We used this information to objectively confirm the chronotype we had identified with the questionnaire,” says Vetter.

Roennenberg points out, however, that “The chronotype is not written in stone.” He adds that internal clocks tick somewhat faster as people get older, and also shift back to an earlier period. Despite that, an owl can never become a lark. Night shifts also become more difficult for owls as the years go by. Scheuerer, who will soon celebrate his 60th birthday, has experienced this. “When I started out at age 24, working through the night didn't bother me a bit, but it's not as easy today,” he says. Sleep requirements are also genetically determined, in addition to being influenced by age. British researchers recently found that sleep requirements decline with age.

The Siemens and LMU researchers now plan to launch a third field trial as a kind of acid test in which, over several weeks, volunteers will be assigned solely to shifts that are harmonized with their internal clocks. This will allow them to determine not only if the incidence of errors does in fact decline as a result, but also if product quality increases and workers feel and sleep better. But putting this knowledge into practice will be a lengthy process. “This is not as simple as one plus one,” says Kloke.

In any case, a double-shift system with an early shift for larks and a late shift for owls can't function for one obvious reason: “People also have a social life and therefore can't and don't want to work only at night. “That's why adjusting shifts in line with chronotype can only be done on a voluntary, individual basis,” adds Kloke. Nevertheless, he believes it's conceivable that the portions of those shifts that are particularly detrimental to a specific chronotype could be reduced.

Moreover, there are tricks everyone can do to get around their daylight circadian rhythm. Sleep researchers recommend, for example, that night-shift workers wear sunglasses after their shift in order to avoid the activating effect of morning light. Bedrooms can be darkened to ensure better sleep during the day. And those who are able to should do what Scheuerer does, namely develop the ability over the years to fall asleep anywhere and anytime—even while sitting on a chair. “When I'm tired and have a break,” he says, “I take a nap for 15 minutes and then go back to work.“