The tourism brochure for the German spa town of Bad Kissingen features a photograph of a young woman on its cover. Dressed in white shorts and a pink vest, the woman is perched peacefully on a sunny rock overlooking a river, reading a handwritten journal. Emblazoned on the top left of the page is the slogan Entdecke die Zeit - Discover Time.

Located in the sparsely populated region of Lower Franconia in Bavaria, Bad Kissingen was once a fashionable resort for the European aristocracy and bourgeoisie. They came for rest and relaxation; soaking up the classical architecture and fragrant rose gardens, and taking the mineral-rich waters, which were reputed to cure all manner of ills. Today, Bad Kissingen has rebranded itself as the world's first ChronoCity - a place where internal time is as important as external time, and sleep is sacrosanct.

Most of us are not free to choose our work or school hours; we have little control over the lighting in our public spaces and external environment; and we are even forced to reprogramme our internal clock twice a year because of daylight saving time. The question that the idea of the "ChronoCity" raises is what changes could society make to better accommodate our body clocks?

Michael Wieden, Bad Kissingen's business manager, came up with the ChronoCity concept in 2013. Having followed scientific developments in the field of chronobiology with interest, Wieden realised that not only could weaving these principles into the town's fabric benefit its residents, it would also make Bad Kissingen stand out from rival spa towns. Bad Kissingen has always been about healing and health, he reasoned; so what better way to heal our modern society than by bringing it back into contact with natural light and sleep. Tourists could come and learn about the importance of internal time, then return home and implement the lessons in their everyday lives. Wieden contacted a chronobiologist called Thomas Kantermann, who was similarly enthused by the idea of launching a revolution in the way that society prioritises sleep.

Quickly, the two men began drawing up a manifesto of the things they'd like to change: schools should start later, children be educated outdoors where possible, and examinations not conducted in the mornings; businesses should be encouraged to offer flexitime, allowing people to work and study when they felt at their best; health clinics could pioneer chronotherapies, tailoring drug treatments to patients' internal time; hotels might offer guests variable meal- and check-out times; and buildings should be modified to let in more daylight.

In July 2013, Kantermann and Wieden, together with Bad Kissingen's mayor and town council, and Kantermann's academic colleagues, signed a letter of intent in which they pledged to promote chronobiology research in the town, and to make Bad Kissingen the first place in the world to "realise scientific field studies in a wider context".

Most controversial of all was their suggestion that Bad Kissingen should split from the rest of Germany and do away with daylight saving time (DST) - the practice of advancing clocks during summer months in order to make the evening daylight last longer.

Since 1884, the world has been subdivided into 24 time zones, all referring to the longitudinal meridian that crosses the Greenwich observatory in London, hence the name Greenwich Mean Time (GMT). Roughly a quarter of the world's population - including most of the inhabitants of western Europe, Canada, most of the US and parts of Australia - also change their clocks twice a year.

The original idea of DST is attributed to Benjamin Franklin, who voiced concerns about energy consumption during dark autumn and winter evenings as early as 1784. Even now, lighting accounts for 19% of global electricity consumption and approximately 6% of worldwide carbon dioxide emissions.

However, it wasn't until 1907 that an Englishman called William Willett self-published a pamphlet, The Waste of Daylight. Willett believed that aligning work hours closer to sunrise (at least in cities) might encourage people to participate in more outdoor recreation, enhancing their physical wellbeing, and might keep them out of pubs, reduce industrial energy consumption and facilitate military training in the evenings.

Willett died of influenza a year before his dream was realised: the UK adopted DST in 1916, followed by the US in 1918. Even so, as Winston Churchill noted, Willett "has the monument he would have wished in the thousands of playing-fields crowded with eager young people every fine evening throughout the summer and one of the finest epitaphs that any man could win: He gave more light to his countrymen".

There was a significant downside, however, as grasped by a fierce opponent of the change, John Milne, who wrote in the British Medical Journal, "for a certain period twice a year, the efficiency of the worker will be somewhat dampened".

By moving the clocks forwards each spring and backwards each autumn, we are creating a form of "social jetlag", to use the term coined by the German chronobiologist Till Roenneberg to describe the gap between our individual body clock and the external clocks and timings that rule our lives. One study of US high-school students - a population that is already sleep-deprived - suggested that their sleep was curtailed by 32 minutes per night during the week following the spring clock change. Maths and science test scores fall in the week following the start of DST among young adolescents, while another study found lower annual scores for the SAT tests, which are used to decide university admissions, among US counties that observe DST, compared to those that don't.

In adults, the transition to summer time and the sleep deprivation it causes has been associated with an increase in accidental deaths and injuries, including road traffic accidents. US judges have even been found to dole out heftier sentences for the same crimes in the week after the transition. From a health perspective, clock changes have been tied to an elevated risk of heart attacks, strokes, suicide attempts and psychiatric admissions.

If it had rejected daylight saving time, as Kantermann and Wieden campaigned for it to do, Bad Kissingen would have become the DST-free town in Europe: "Every individual and business would have got a big publicity boost from doing that," says Roenneberg, the chronobiologist, who also supports the scrapping of the biannual changeover.

Deliberately putting oneself in such temporal isolation may sound extreme, but there are precedents. For more than half a century, the US state of Arizona has declined to join the rest of the country in its annual spring leap forward to DST - although the Navajo Nation, which is largely inside its borders, does. (The Hopi Reservation, which is surrounded by the Navajo Nation, follows the rest of Arizona in remaining on winter time.)

In the end, the Bad Kissingen town council defeated the motion about becoming DST-free. But even if the town isn't ready to become a poster child for the anti-DST movement, momentum is building elsewhere - in Finland, for instance, where it's light virtually all of the time during summer, but they still suffer the social jetlag caused by the time shift. The European commission also recently proposed abolishing DST - although it requires support from the 28 national governments and MEPs before anything changes. Meanwhile, in southern England many would like to see the entire country shifted permanently forward into Central European Time, given that, in Britain, the annual changing of clocks back to winter time means that it gets dark as early as 4pm in December and early January.

This all goes to highlight a central point: our biology is tethered to the sun, yet the clocks society uses to keep time are influenced by a tangled web of political and historical factors. Take Germany as an example. At its widest point, the country extends across nine degrees of longitude, and the sun takes four minutes to pass over each of them, which means that the sun rises 36 minutes earlier at its eastern border than at its western one. In a country with the same time zone - and the same TV and radio shows, school start times, and work culture - you might expect that everyone would rise at more or less the same time, but Roenneberg has demonstrated that people's chronotype - their innate propensity to sleep at a particular time - is shackled to sunrise. On average, Germans wake up four minutes later for every degree of longitude you travel west, meaning that those in the extreme east rise 36 minutes earlier, on average, than those living in the extreme west of the country. A similar pattern has been documented in the US, where those living on the eastern edge of its time zones get up earlier than those on the western edge, where the sun rises later.

In some cases, this discrepancy between external and internal time is enormous. A key reason why the Spaniards eat dinner so late is because - positioned as they are at the extreme west of the Central European time zone - 10pm is in fact 7.30pm according to their internal time, which is set by the sunrise.

If the UK advanced its clocks to match Germany and France, this would expose people to more light in the evenings, but not the mornings, pushing our internal clocks even later. Yet we'd still be having to get up at the same time each day to go to work or school, potentially making social jetlag even worse. And in mid-December, a switch to CET would mean that the sun would rise in London at 9am, and in Glasgow at 9.40am. Many office workers would be arriving at their desks while it was still dark outside. The sun would then set at 5pm in London, meaning that the standard nine-to-five worker who didn't go outdoors at lunchtime would spend several months of winter seeing practically no daylight at all.

Russia, which switched to permanent summer time in 2011, performed an abrupt U-turn just three years later, citing the ill health and accidents it caused. Sergei Kalashnikov, the chair of the State Duma health committee, claimed that the switch condemned Russians to increased stress and worsening health, because of having to travel to work or to school in pitch darkness. It was also blamed for an increase in morning road accidents. Since 2014, at least some parts of Russia have switched to living on permanent winter time. However, Muscovites now complain of the insomnia brought about by early sunrises during summer, and sales of blackout blinds have soared, which just goes to illustrate the complexity of the issue and how hard it is to get right.

illustration of an eye reflecting the moon

Illustration: Dennis Vernooij

There are few members of society who more obviously find it hard to conform to its early-bird demands than teenagers. Perhaps it's unsurprising, then, that one of Bad Kissingen's most enthusiastic early adopters of the ChronoCity idea was the local secondary school, the Jack Steinberger Gymnasium, which caters for around 900 pupils aged 10 to 18. Here, a group of older students created a questionnaire and canvassed their fellow pupils about whether it would be desirable to start school at 9am rather than 8am: the majority said it would. They also chronotyped the entire school and calculated the amount of social jetlag its pupils were suffering from each week. Approximately 40% were experiencing two to four hours of social jetlag, while a further 10% were contending with four to six hours - equivalent to flying from Berlin to Bangkok and back - each week.

Teenagers are at greater risk of social jetlag than adults because their biological rhythms are naturally shifted later. This makes it harder for them to fall asleep at night, and yet they still must get up in the morning to go to school. To compensate for the sleep deprivation this causes, they then sleep in at weekends.

Teenagers' later chronotype also means that their natural peaks in logical reasoning and alertness occur later than they do in adults. In one study, Canadian researchers compared the cognitive performance of teenagers and adults during the mid-morning, and again, mid-afternoon. The teens' scores improved by 10% in the afternoon, whereas the adults' scores deteriorated by 7%.

One strategy for dealing with this issue is to delay school start times and allow teenagers to sleep for longer in the mornings. The US state of Minnesota was among the first to investigate the benefits of doing so, after the Minnesota Medical Association sent a memo to all school districts urging them to do something to improve adolescent sleep. As a result, in the late 1990s, several high schools in the Minneapolis suburb of Edina changed their start time from 7.20am to 8.30am. When researchers from the University of Minnesota investigated the impact of the change, they were surprised to find almost unanimous support for it among students, teachers and parents. Students said that they felt less tired during the day, while teachers reported that the children seemed more engaged and focused. School attendance also improved.

As news of this success began to spread, other schools started changing their hours as well, but no one had done a proper before-and-after study confirming that it made a real difference. When Judith Owens, a paediatrician with a particular interest in sleep medicine, was called in by her daughter's high school to talk to staff about the potential benefits of starting school 30 minutes later, she decided to see if they could produce some more robust evidence. "Many felt that half an hour wasn't going to do anything - it would just disrupt the school schedule," Owens recalls. She suggested that they collect data on the students' sleep and mood before and after a three-month trial of the later start.

Owens was pleasantly surprised by the results. Just a 30-minute delay in starting school resulted in pupils getting an extra 45 minutes of sleep per night. The percentage of students getting less than seven hours of sleep decreased from 34% to just 7%. The kids also rated themselves as more motivated to participate in a variety of activities. But the thing that really swung it for Owens was the change in her own daughter, Grace. "She was like a different person," she says. "It was no longer a battle to get her up in the morning; she would be able to eat breakfast; and the start of the day was just pleasant, instead of torture for everybody."

Owens changed her research focus and became involved in drawing up policy on school start times for the American Academy of Pediatrics, based on the best available evidence. In 2014, they issued a policy statement: starting school before 8.30am is a key modifiable contributor to insufficient sleep, as well as circadian rhythm disruption, in the adolescent population.

But if school should start later in the day, what time would be best? Most British students don't start school until around 8.50am, but one recent study concluded that most 18- and 19-year-olds don't feel mentally sharp until much later, and therefore possibly shouldn't start their studies until after 11am. In a separate study, the same researchers tested whether moving the start time of an English comprehensive school from 8.50am to 10am made any difference to its 13- to 16-year-old pupils. Rates of absence due to illness fell dramatically following the change: whereas before they had been slightly above the national average, two years after the change they were down to half the national rate. Pupils' school performance also improved.

Even a 10am start would be difficult to impose in countries such as the US, where most adults also start work earlier than in Britain. It would require a change of mindset among parents - as well as a more flexible attitude by employers - but the data suggests that it would make a difference to many pupils.

The tide may be turning in schools, but in the workplace, there's still a way to go. An individual's chronotype is based on their sleep behaviour on free days, and a simple way to define it is to look at when the mid-point of sleep occurs: if you fall asleep at midnight at weekends and wake up at 8am, your mid-sleep time would be 4am. Roenneberg has discovered that for 60% of people, the mid-sleep time on free days is between 3.30am and 5.30am.

Expecting people to wake at 6.30am and then to be mentally sharp when they arrive at work at 8am or 9am involves something of a fight against nature. Like physical performance, your mental skills peak and trough at various times throughout the day. Logical reasoning tends to peak between 10am and noon; problem-solving between noon and 2pm; while mathematical calculations tend to be fastest around 9pm. We also experience a post-lunch dip in alertness and concentration between about 2pm and 3pm. However, these are averages, so an early riser's peak in problem-solving may arrive several hours earlier than a night owl's.

Research into this area is only just beginning, but managers with early-bird tendencies have been found to judge employees who start work later as less conscientious, and to rate their performance lower, compared to those who share such managers' sleep preferences. Not only would a greater appreciation of these individual differences, and allowances for different schedules, help to level the playing field, it could boost workplace productivity, and employees' health and happiness: "If you are forcing an evening person to show up at 7am, all you have is a grumpy employee who sits there and drinks coffee, procrastinating until 9am because he simply can't focus," says Stefan Volk, a management researcher at the University of Sydney Business School.

Allowing staff to choose their work hours based on their individual sleep preferences is one solution. But is it worth the potential disruption it might cause? In a recent study, American researchers piloted a three-month intervention at a global IT firm, which aimed to improve workers' sleep and work-life balance by helping them to move from a time-based to a more results-based office culture. Rather than judging colleagues on how they spent their time, workers were encouraged to work at whatever time or place they wanted, so long as they achieved specific results, such as delivering finished projects to customers.

Following its introduction, workers' average sleep time increased by eight minutes per night - adding up to almost an extra hour of sleep over the course of a week. But, perhaps more importantly, the number of times that people reported never or rarely feeling rested upon waking went down. As one employee who previously had to get up at 4.30am in order to get an early start at work and avoid the evening rush hour put it: "If I'm working from home I don't get up until 6 or 6.30 and I start working at 7 ... I get more sleep than I've had in years."

In Bad Kissingen, Wieden's current focus is on establishing a centre for chronobiology in the town, which would provide an academic hub for chronobiology research across Europe. The proponents of the ChronoCity project hope that this will galvanise the town: "If we have a professor of chronobiology based here, who will go out into the community to give lectures and initiate research, it should be easier to open doors to hospitals and businesses and have a greater influence on health," says the mayor, Kay Blankenburg.

There have been some other victories as well. The Stadtbad, which oversees tourist and spa facilities in the town, now offers flexible working to its office staff; while Thorn Plöger, the manager of Bad Kissingen's rehabilitation hospital, took the idea so seriously that, at one point, he adjusted all the hospital's clocks, making some a little fast and some a little slow, in order to provoke reflection. "People are always so stressed about the time," he explains. "They would say, 'it's 9 o'clock, I must get my medicine', or 'I have a date at midday, so I must leave'; I told them: 'Take it slowly: entdecke die Zeit.'"

Did they respond well, I ask?

"No," he says, with a mischievous smile, "they said: 'You have to change the clocks back.'"

Plöger sighs and shakes his head. "Germany has a problem. People are always watching the clock." For the ChronoCity initiative to work, he explains, it requires a more flexible mindset: one that says it doesn't matter when you start work, so long as you get the job done. It's about internal time, not what the clock on the wall says.

Adapted from Chasing the Sun by Linda Geddes, published by Wellcome Collection and Profile Books and available at

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