16
The Scissors of Sleep
After graduating from high school, Timothy had visited Benjamin at Princeton University and had worked in his friend’s small start-up company. Ever since they lived on the same street in a suburb of Eugene, Oregon, they had been the closest friends, even though Benjamin had been the classmate of Timothy’s elder brother. The six months in Princeton had been Timothy’s first taste of independence away from home and had been heaven on earth. He loved Princeton, with its university and its sidewalk cafés.
Benjamin had opened a small shop called LayIn&Out—a sophisticated kind of copy shop and café. Besides providing all the normal photocopying possibilities, customers (predominantly students) could bring documents or slide presentations for professional improvement on layout. Benjamin had gotten the idea after watching an Indian Bollywood movie that told the story of an old-fashioned “letter writer” who provided communication services in a faraway little village where only a few people could read and write. Afterward in the bar, he discussed with friends how this profession still persisted in other ways in modern society, for example when experts advised customers on layouts for their documents, presentations, or personal websites.
Besides being an excellent coffee bar, LayIn&Out offered several desktop computers, each of which had a Skype connection to one of Benjamin’s young employees, who had to be on call when the shop opened at seven in the morning. The early morning hours had the highest customer traffic because many students worked all night on a paper or a presentation due the next day. To give it the final polish, they took it to LayIn&Out for professional improvement while trying to compensate for the sleepless work night with an excellent latte and a delicious croissant.
Timothy was good at polishing layouts and had always been an early type compared with the rest of his peer group. So, during the six months of his Princeton visit, he quickly became an irreplaceable cog in the up-and-running machinery of the young company. Although he loved his life in Princeton, he decided to return home after half a year. Amy and Timothy had always been very close, but it took the long separation and endless Skype sessions for them to realize that something more than friendship had developed between them. Benjamin insistently but unsuccessfully tried to persuade Timothy to stay—his role at LayIn&Out was crucial. In the end they worked out a compromise that involved frequent visits to Princeton (billed to the company’s expense account) and a continuation of Timothy’s expertise—online from Oregon. So Timothy went back home with a well-paid job and a brand new super-fast computer in his luggage. From the day of his arrival in Eugene, Timothy sat at his computer every work day (LayIn&Out was closed on Saturdays), advised customers via Skype, worked on their documents’ layouts, and delivered the final product in the shortest possible time.
Another half a year into the existence of LayIn&Out, it became clear that the concept was a terrific success and that the young company was making a huge profit. The only thing standing between Timothy and complete happiness (including Amy, of course) was his working hours. He got up at 3 A.M. every work day to be ready, and sort of awake, in front of his computer at four—just in time for the shop’s opening time in Princeton. He then worked hard and concentrated for at least six hours without interruption. The consequence of this strict and early schedule was chronic exhaustion—he never got enough sleep, despite his early chronotype. Timothy could catch up on his sleep only on weekends by sleeping in a completely dark room. But he never slept beyond eight, even though that was much later than he would usually wake had he not been so exhausted. His relationship with Amy began to suffer seriously because he tried to be in his dark bedroom at around nine every evening, although he never could get to sleep until about 10 P.M. His best breaks from this gruesome regime came on his frequent visits to Princeton, where he would participate in meetings that tried to improve LayIn&Out’s policies and concepts. Even then, he worked as one of the on-call partners who were available for the customers via Skype at seven in the morning. But at least he was getting enough sleep and felt much fresher during the day compared with his online participation in the scheme from Oregon. This difficult situation went on for about another nine months until the company was so successful that they decided to open branches across the country. Eventually, Timothy became the West Coast manager of LayIn&Out with his own stores in his own time zone. He still continued to work as an online representative, but the relaxed working hours gave him so much more energy that he had no trouble combining his double role as online layout expert and West Coast manager while still finally finding enough time to spend with Amy.
At the beginning of this book, I covered a lot of the biology underlying the ticking of the body clock. But as the book progressed you have read more and more about the interferences between body clock and social clock—between internal and external time. The last chapter focused on jet lag and explained what happens when we travel too fast across time zones. This chapter looks more closely at the discrepancies between internal and external time that can occur even if we never board an airplane and stay in the same place for our entire life.
You meanwhile know that sleep duration and sleep timing (chronotype) are two independent, heritable traits. However, this is only true if we consider the average sleep-need of an individual, calculated across both work and free days. The independence of the two traits breaks down if we analyze work days and free days separately: sleep duration can be very different, and this difference very much depends on chronotype. The later someone’s chronotype (horizontal axis of the graph; the vertical axis represents sleep duration), the less sleep this individual gets during the working week (black dots). There is a simple explanation for this observation: later chronotypes fall asleep later than early chronotypes—even on work days. Yet working hours are, on average, the same for everyone, which is why most people use an alarm clock to wake up in time for work. (Our database shows that this is true for 85 percent of the population.) Consequently, the later someone’s chronotype, the shorter his or her opportunity for sleep on a work day.
Sleep duration on free days (open circles in the graph) reflects the systematic sleep deprivation that different chronotypes accumulate on work days. Very late chronotypes don’t get much more than 6.5 hours during workweek nights and therefore sleep for nine hours or more on their free days. Some individuals have to sleep through half of their free days to catch up on their sleep loss.
The scissors of sleep. Depending on chronotype, sleep duration can be very different between work days and free days.
In contrast to later chronotypes, early larks experience sleep deprivation on free days. Again the explanation is simple: the majority of later chronotypes in the population puts pressure on early types. Evenings preceding free days are especially difficult: don’t be so bloody boring; come with us to the bar, the cinema, the theater . . . Late and early chronotypes almost lead mirror lives between internal and external timing. The body clock tells late types when to fall asleep, and the alarm clock tells them when to wake up. In contrast, social pressure exerted by their owlish friends tells larks when they are allowed to fall asleep on evenings before free days, and the body clock tells them when to wake up. It almost doesn’t matter when early types go to bed—they more or less wake up at their usual time the next morning.
To validate how accurate and representative the answers of subjects are when they fill out the Munich ChronoType Questionnaire, we periodically ask people to keep sleep logs for at least six weeks. Our current collection of these logs totals more than a thousand. We find that the correspondence between what people state in the questionnaire and what they state in their daily sleep logs is almost perfect. These logs not only allow us to validate the questionnaire, they also tell us very personal stories about the temporal life of different people. When we sort these sleep logs according to chronotype, clear patterns of sleep behavior across the working week and the weekend become apparent. Let’s look at three representative examples. In al
l these examples, sleep on work days is shown as black bars, and gray bars represent sleep on free days. The successive days of the self-recorded sleep times are shown from top to bottom (vertical axis), and local time—from 6 P.M. to 6 P.M.—is indicated on the horizontal axis.
The first example represents the sleep times of an extreme late chronotype who can freely choose her own work times. This individual falls asleep, on average, between 3 A.M. and 4 A.M. and wakes up between 11:00 and noon. Neither sleep timing nor sleep duration differ significantly between work days and free days; both sleep onset and sleep end show a natural day-to-day variation. As you will see, this is the least constrained sleeping situation of all. This individual sleeps within her body clock’s window for sleep practically all the time.
The sleep times of an extreme late chronotype who can freely choose his own work times. Black bars represent sleep on work days, and gray bars represent sleep on free days.
The subject in the next example is an extreme early type who goes to bed sometime between 8 P.M. and 10 P.M. and wakes up between four and five in the morning—long before workplaces usually start the day. I am always amazed about the huge differences that individuals show in their sleep–wake behavior. The individuals who produced the sleep logs in these first two examples could almost share a bed without ever having to sleep together. As in our first example, sleep onsets and sleep ends of the early type show a natural day-to-day variation. In this case, however, a systematic pattern on weekends appears: early types become sleep deprived on free days as a consequence of the social pressure exerted by their owlish friends, who are the majority.
The sleep times of an extreme early chronotype. Black bars represent sleep on work days, and gray bars represent sleep on free days.
Typical for a bell-shaped distribution, extremes at both ends are rare. Extreme late types who can freely choose their work times may be even scarcer—work times are too early for 60 percent of the population. Thus, the majority has difficulty complying with given working hours. The “scissors of sleep” show that the later the chronotype, the greater the differences in sleep duration between work days and free days. But sleep timing can also show huge differences between the working week and the weekend in late chronotypes. The scalloped shape in this third sleep-log graph is far more typical for the majority of the population than the two first examples.
Sleep onsets on work days show the usual day-to-day scatter. Sleep ends on work days, however, fall—with some exceptions—onto a straight vertical line that can only be explained by assuming the regular interference by some kind of waking-up aid (WUA; I tried to invent some positive-sounding term for the obnoxious little gadget called the alarm clock).1 The use of a WUA in the morning depends, of course, on chronotype. While few larks use a WUA on work days, almost all owls do. Modern WUAs, which are equipped with a “snooze” function, would give us an even more quantitative characterization of just how chronotype-dependent waking-up rituals are. I am convinced that if we were to query people on how often they use the snooze button on workday mornings, we would get a perfect curve, with extreme early types never making use of this possibility and extreme late types using it many times before finally getting out of bed. The fact that many early types actually use an alarm clock (despite always waking up before it rings) must lie in some unfounded paranoia about not waking up in time for work.
The most characteristic feature of the sleep–wake behavior of late chronotypes is the strange scalloped shape of their sleep times. Their large shifts are somewhat reminiscent of what Oscar and Jerry experienced by flying from one time zone to the other. The patterns in the sleep logs of later chronotypes almost look as if these individuals had flown from the East Coast to the West Coast of the United States on Friday, and then back again on Monday.
The “scalloped” sleep–wake behavior of late chronotypes who use an alarm clock to wake. Black bars represent sleep on work days, and gray bars represent sleep on free days.
I am often asked whether we cannot get used to given working hours merely through discipline and by confining our sleep habits to certain times. The assumption inherent in this question is that the human body clock can synchronize to social cues. I tend to find that any such questioner, who usually also displays a somewhat disdainful tone toward the weakness of late chronotypes, is an early type—someone who has never experienced the problems associated with the scallop-shaped sleep–wake behavior of late chronotypes.
The story of Harriet and her golden retriever made it quite clear that social cues can be ruled out as a good zeitgeber. Otherwise blind people would certainly use these cues to relieve themselves of the misery of having a body clock that runs at its own pace through a twenty-four-hour society. Social cues have been shown to entrain human clocks, but notably only in sighted people. Oil rig workers are a good example. They work offshore for several weeks at a time, during which they work for most of their active day before retreating to their bunks. They can be put on almost any shift schedule without problems because their body clock readily entrains (as long as the work schedules don’t rotate too fast). Yet their body clock is only entrained indirectly to the social times of their shift. The main zeitgeber is still the light–dark cycle, which they create themselves by being exposed to light during work and to darkness while they sleep. Note that despite the synchronization of the body clock to socially dictated light–dark cycles, the phenomenon of early and late chronotypes remains—only now in relationship to the social schedule rather than in relation to the day-night cycle on our planet. The phase of an individual’s body clock in relationship to a zeitgeber is a biological phenomenon and not a matter of discipline.
The circadian clock in normal workers is rarely oblivious to daylight. That is why their body clock entrains to the natural alterations of day and night and not to social work times. Many of the sleep logs in our collection that display the typical scallop pattern were kept by individuals who have been working with the same early and regular work hours for decades without ever getting used to them. As a result, these individuals appear to fly west across several time zones every weekend, returning east every Monday. Because this pattern is so much like time-zone travel, we have introduced the term social jet lag. Unlike what happens in real jet lag, people who suffer from social jet lag never leave their home base and can therefore never adjust to a new light–dark environment, as Jerry and Oscar could have done if they had only stayed long enough in Japan. While real jet lag is acute and transient, social jet lag is chronic. The amount of social jet lag that an individual is exposed to can be quantified as the difference between midsleep on free days and midsleep on workdays (the change in midsleep in the graph below, which is based on the third sleep-log example). Over 40 percent of the Central European population suffers from a social jet lag of two hours or more, and the internal time of over 15 percent is three hours or more out of synch with external time. There is no reason to assume that this would be different in other industrialized regions.
The condition of social jet lag is comparable to having to work for a company that lies several time zones to the east of one’s residence. Timothy the layout expert is an early type. He could therefore sit fresh as a daisy in front of his computer when LayIn&Out opens its doors at seven o’clock. But that was true only when he lived in Princeton, New Jersey. Once he had to supply the same services out of Eugene, Oregon, he had serious difficulties in being awake and ready for work. Timothy’s story shows even early types the difficulties that a large portion of our society has to face every morning when trying to get ready for work. The main symptom of social jet lag is chronic sleep deprivation, which can be the cause of many health and mood problems. We are only beginning to understand the potentially detrimental consequences of social jet lag. One of these has already been worked out with frightening certainty: the more severe the social jet lag that people suffer, the more likely it is that they are smokers. This is not a question of quantity (number of cigarettes per day) but sim
ply whether they are smokers or not. In relation to smoking there are only three types: those who never smoked, those who have successfully quit smoking, and those who still smoke. Statistically, we experience the worst social jet lag as teenagers, when our body clocks are drastically delayed for biological reasons, but we still have to get up at the same traditional times for school. This coincides with the age when most individuals start smoking. Assuredly there are many different reasons people start smoking at that age, but social jet lag certainly contributes to this risk. Later on in life, the less stress smokers have, the easier it is for them to quit. Social jet lag is stress, so the chances of successfully quitting smoking are higher when the mismatch of internal and external time is smaller. The numbers connecting smoking with social jet lag are striking: among those who suffer less than an hour of social jet lag per day, we find 15 to 20 percent are smokers. This percentage systematically rises to over 60 percent when internal and external time are more than five hours out of synch.
Social jet lag is defined as the difference between midsleep on work days and midsleep on free days. This definition allows quantification of the discrepancy between an individual’s social and biological timing. Dark gray bars represent sleep on work days, and light gray bars represent sleep on free days.
17
Early Socialists, Late Capitalists
Olaf Toemmelt is the director of GoEast, an extremely successful public relations agency based in Magdeburg, East Germany. The State of Saxony-Anhalt has launched a competition for a public relations campaign that would help to attract more businesses and boost the state’s economy. Together with his team, Olaf had been brainstorming for almost a week now, but none of the ideas had been convincing enough to develop into anything that could be used for the competition. It was a beautiful summer morning, and he drove to work in his open BMW convertible from his country house—an old vicarage he had acquired for an extremely reasonable price just after Germany’s unification—along the highway toward Magdeburg. His blond hair—he had seen his hairdresser only yesterday—was protected by an original NY Yankees baseball cap from the 1930s that he had bought at an auction on one of his frequent visits to the United States. His thoughts were occupied with the still-unborn PR campaign, so he was only half-listening to the morning news program. “A new poll was published yesterday,” the radio announced, “investigating when Germans get up. It showed notable differences among the different German states.” Olaf was still not listening properly. “On average Germans get up at 6:48; the latest out of bed are the citizens of Hamburg, Berlin, and the state of Hessen; among the earliest are Thüringen and Saxony. The all-German champion of early risers is Saxony-Anhalt, where people get up nine minutes earlier than the German average.” “Ha,” thought Olaf, “they get up earlier than the rest of the country—so what? That’s only because the ‘Ossies’ still live by the rules of the German Democratic Republic. They have had to get up early all their lives—it was party line.”1
Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired Page 14
