Another hour less sleep: On the night from Saturday to Sunday the clock changes from two to three o’clock and summer time begins. Some people look forward to the longer, bright evenings, others complain about being tired. How does the change affect our biological rhythm? Chronobiologist Martha Merrow from the Institute for Medical Psychology at the Ludwig Maximilians University in Munich warns against trivializing the consequences and speaks of “social jet lag”.
Chronobiologist Martha Merrow warns against trivializing the consequences of the time change.
(Photo: LMU)
SZ: Ms. Merrow, we are changing the time on the clocks. But they say that by doing so we disrupt our internal clock. What do you mean by that?
Martha Merrow: Our bodies function according to a special rhythm that depends on natural light. In chronobiology, we call this the internal clock, or more precisely the circadian rhythm. It controls all important processes in the body, such as the sleep-wake rhythm or body temperature. Even our organs all have a circadian rhythm. And now we come along and artificially decree that our day always starts an hour earlier for half a year. This totally messes up our internal clock.
Can you make this clear with an example?
I wake up at seven in the morning. In summer time this time is called eight o’clock. But because of real obligations like work or school, I still have to get up at seven o’clock at our artificially set new time. So I continue to set my alarm for seven. And because that’s an hour earlier according to the natural clock, i.e. actually at six, I’m constantly tired.
A little tired, so what? Most people quickly get used to the new process.
It’s not just a little tired. You have to imagine that our bodies, all our physical functions and systems, are then an hour late. For studying, for eating, for sleeping, for doing sports. And because we tend to stay awake longer in the evening because it’s still so bright, we have a hard time making up for the lack of sleep. With every alarm clock that wakes us up too early, we make it worse. Some people never recover from this chronic social jet lag.
What is that?
We chose this term in the chronobiology research group at the LMU together with Professor Till Roenneberg to describe the gap between the internal and social clock. We harm ourselves when we enlarge them.
What consequences can this have?
Sleep deprivation has a negative impact on our productivity, our ability to absorb and our memory. Studies also show that a lack of sleep over a long period of time can lead to obesity, more nicotine or alcohol consumption, and even depression.
What can you do to get through the initial period after the changeover?
There are three influencing factors: genes, age and the lighting environment. We only have influence on the latter. So I recommend wearing glasses with orange lenses that filter out blue light waves in the days before and after the change. Appropriate filters on your smartphone or laptop are also useful, especially in the evenings. This means you get tired noticeably earlier and can adjust more easily. And otherwise it is important to go out in the morning the day after the change and soak up as much daylight as possible. This natural light has a huge influence on our internal clock, but we tend to underestimate its effect.
Are there people who suffer less or more from the time change?
Older and younger children usually have it a little easier because they tend to have an earlier chronotype. However, the chronotype of adolescents and young adults is, on average, about 2.5 hours later than that of older adults. They have it particularly difficult. And this is a phase of life in which they have to learn and achieve a lot at school or in training. It is therefore high time to abolish the time change.
The European Commission had already proposed ending the change in 2018. But the ball was passed to the member states, who should decide. Since then, the debate has been on hold.
I understand that there are difficulties in abolishing the change. But it just doesn’t make any sense. Firstly, what was originally promised, namely saving energy, has not materialized. And secondly, you could actually do people a big favor by abolishing it. If we want a smarter, more capable and healthier society, we must end this chronic sleep deprivation.