What can you derive from the chronotype for everyday life?
Kanterman: Let’s say the hair test shows that a person’s melatonin exceeds a certain threshold at 9 p.m. Then we recommend a bedtime of 11:30 p.m. to 7:30 a.m. You should not do any sport in the three hours before. However, the best time to exercise also depends on what kind of sport it is: strength training in the morning, endurance sport in the afternoon.
And what about mental performance?
Kanterman: On average, cognitive performance is highest between 10 a.m. and 12 p.m. In this case, an average adult, assuming eight hours of sleep, would peak mentally at around 11:00 am.
What if the chronotypes of a couple are very different: Can owls and larks be happy together?
Chandler: Naturally. It is important that both develop an awareness that they are different chronotypes. No one should torture themselves for the sake of the other person, for example getting up regularly in the morning although they still need sleep, or staying up late in the evening for the other person even though they are already tired. Both have to accept the differences, then they can also see the positive sides.
Kanterman: For example, one can take care of the children in the morning and the other in the evening! We have to realize that these are hard-wired biological programs. If we live against the body clock for a short time, we may be in a bad mood. But if sleep is systematically neglected for weeks or months, this can have dramatic consequences in the long run, such as an increased risk of metabolic and cardiovascular diseases, depression and sleep disorders. This is also referred to as “social jetlag”. Unfortunately, school is such a negative example.
»Whether someone is a late or an early type makes a difference of up to one grade in exams in the morning«(Thomas Kantermann, chronobiologist and psychologist)
So it’s proven that school starts too early in the morning?
Kanterman: School starts at 8 a.m. for younger children. In contrast, 16-year-olds at 8 in the morning feel like 45-year-olds at 4 or 5 at night. Hardly any teacher would do that. We looked at performance: Whether someone is a late or an early type makes a difference of up to one grade in morning exams. The inequality stops after lunch; in the afternoon hours we no longer see any difference.
Chandler: This means: If a class test is written in the first lesson, the genetics of the inner clock decide who does better or worse.
What would be the solution?
Chandler: From grade 7 it would be good to start as late as 9am and from grade 9 around 10am. If it is not possible to postpone the start of school, at least class tests should not be scheduled until 10 a.m.
Kanterman: And if you start early, please don’t do math, but do sport or exercise outside to activate your inner clock. Alternatively, one could start with subjects that require more creative thinking, such as art or philosophy. We implemented this at a high school in Bad Kissingen: It worked well.
Does getting up early also have consequences in areas of life outside of school?
Kanterman: Yes, for example on the road. A study in the USA, where young people from the age of 16 are allowed to drive a car, compared accidents on the way to school. In the afternoons on the way home, accident rates are greatly increased when schools start before 8am instead of between 8am and 9am. The children are then more tired when they go home in the afternoon.
Why is it that German schools continue to start so early? The political will?
Kanterman: Yes, and on the logistics. It depends on how public transport is organized. In a big city, starting school later is easier to implement. But there are also advanced arguments, for example that the parents have to leave the house early. However, the young people we are talking about here could later set out on their own. The resistance is mainly in people’s heads, according to the motto: getting up early didn’t do us any harm in the past. However, starting school early was already wrong 100 years ago. Maybe the consequences weren’t that great, because back then you were outside more and didn’t stay up that long in the evenings with artificial lighting.
Chandler: And because there were no smartphones back then. We often use the devices until just before we go to sleep. The problem: Unless you have activated sleep mode, they emit blue light, which certain cells in the retina react to. When the blue light hits the cells in the evening, they “think” it’s still day and shift their internal clock backwards.
Plea for normal time
The clocks are changed twice a year: one hour forward in spring and one hour back in autumn. This further throws the body clock off the beaten track in many people who are already struggling with social jetlag. Thomas Kantermann and Achim Kramer therefore advocate living the whole year in Central European standard time – also known as winter time. “But one shouldn’t talk about summer and winter time,” says Achim Kramer. Because many people would vote for summer time in polls because they prefer summer. But one has nothing to do with the other. If »summer time« applied all year round, it would only be light very late in winter, a problem especially for late chronotypes with social jet lag. More on that: a comment.
So be sure to turn on sleep mode. Other Recommendations?
Chandler: Spend some time outdoors first thing in the morning, then your internal clock will be synchronized with daylight. For example, you can get off the train one station earlier on your way to school or work and walk the last kilometer. Even if it doesn’t seem like it, daylight is very bright even on a dull winter’s day, around 10,000 lux. Indoors, with normal lighting, it’s a maximum of 500 lux.
Kanterman: The daylight in the morning can compensate for the artificial lighting in the evening to a certain extent, so that the sleep-wake cycle is maintained. We usually have particularly bright lights in the bathroom, for example. This is unfavorable, because even if you only go to the toilet for a short time, the melatonin is immediately suppressed. Then it takes longer to fall asleep again. In cities, you don’t actually need any light in a room with a window to find your way around: Because of the light pollution outside, it’s bright enough inside. But it also helps to dim the lamps or turn them towards the ceiling and to do without all light sources that are not required. I like to recommend my students to do a digital detox for a week, starting two to three hours before bed: no television, no computer, no smartphone, instead have candlelit conversations or read a book. Many benefit from it, they fall asleep faster and are more rested in the morning.
Circadian medicine: Diseases in tune with the internal clock
In some diseases, the entire day and night rhythm of the organism is disturbed, for example in Alzheimer’s disease: Those affected are tired during the day and awake at night. They are particularly confused and disoriented at sunset. Other symptoms of the disease also become worse at certain times of the day. In the rheumatoid arthritis the joints hurt more in the morning. A pill would then come too late – the inflammatory messenger substances increase at night. That’s why researchers at the Berlin Charité have developed drugs that are taken in the evening but only release their active ingredients hours later.
Extreme chronotypes can also be caused by a sleep-wake rhythm disorder to have. This includes the advanced sleep-wake phase syndrome, a hereditary disease: those affected fall asleep early in the evening and wake up again at 2 a.m. That’s rare Non-24 Hour Syndrome, short non-24. It is mainly found in blind people because they lack light as an external timer. That’s why her clock runs slower; they get tired an average of 12 minutes later each day. However, the 24-hour rhythm can be adjusted with medication: Circadian medicine is not only looking for therapies that follow the rhythm of the internal clock, but can also readjust the internal clock. More on this: Healing to the rhythm of the internal clock.