Jörg Stehle likes to divide people into bird species. The larks are early risers who cannot lie down in the morning without becoming restless. The owls sleep late and can’t find their way to bed in the evening. In between there is the largest flock, the pigeons, as Stehle calls those who have the least difficulty with the time demands of a regular school or work day – because it suits their best form on the day. But larks and owls may spend their entire lives fighting against time constraints that contradict their internal clock. They suffer from so-called social jet lag, explains the chronobiologist, who has been studying the topic for years.
Anyone who has teenagers who sleep all the time at home knows the hardships that result. Stehle has great sympathy for them: “They are more owlish in their youth than they have ever been in their lives.” Although more boys have difficulty getting up early than girls. In Scandinavia, where the encouraging morning light is even more lacking in winter than here, people have reacted to this. The start of school has been pushed back, and the focus is also on putting on the agenda in the first hour not mathematics, but subjects that do not demand top performance from the child’s mind.
Chronotype is genetically predetermined
But social jet lag is much more than the discomfort of a late riser awakened from his dreams. The genetically determined chronotype, roughly classified by Stehle with the bird species, determines a person’s mental and physical performance over the course of the day. The driving force behind this is an internal circadian clock, which has its core area in the hypothalamus of the diencephalon. It determines a person’s sleep-wake rhythm over 24 hours. Chronobiology studies such rhythms and is also interested in how they are influenced.
Those who constantly have to work against their internal clock often use aids to get on the right track of time. For example, the owl drinks a lot of coffee in the morning to wake up and alcohol in the evening to fall asleep, says Stehle. But these popular wake-up and sleep-inducing products are far less healthy than, for example, blue light, which chronobiologist Stehle prefers and which he uses with specially made glasses.
For competitive athletes – Stehle is one himself – it is immensely important to know and be able to influence the different performance levels throughout the day. It often decides between the winner and second place. The chronobiologist now advises athletes on this and also helps them to overcome jet lag more quickly, which weighs heavily on athletes due to the time difference when traveling to competitions on other continents.
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In all of this, the neuroscientist is primarily concerned with health. Shift workers have a significantly increased risk of cancer and are more prone to obesity because they eat at times when the body is actually ready to rest. According to studies, they are sick more often and age faster, says Stehle. Particularly strenuous: shift work that changes from one day to the next. It is therefore important to chronobiologist Stehle to make the topic better known to the general public so that employers become more interested in working time models that take advantage of employees’ performance – without having to make them work against their internal clock.