Study about time change - Which time is better for our health?

Study on time change The morning light sets the pace As of: October 24th, 2026 • 10:55 a.m

What was once supposed to save energy is now a nuisance for many. In 2018, the EU Commission proposed abolishing the time change. But what time should apply? Researchers have an answer.

Being woken up by an alarm clock is unpleasant. It's even more difficult to drag yourself out of bed when it's dark outside. Because light makes a subtle difference - science confirms this.

To understand what time does to our bodies and our health, we need to look inside ourselves: the biological clock. In science it is called the circadian clock. It determines our sleep-wake rhythm and has to be adjusted every day, as Henrik Oster, chronobiologist at the University of Lübeck, explains.

That night the clock was set forward another hour. more

Because our internal clocks naturally run a little slower than 24 hours. In order to keep up with the daily rhythm, they adapt daily - and this happens through the light in the morning.

"You have to imagine it like a clock that runs a little too slowly and would shift by an hour every day. In the morning you go to it, wind it up and move the hand a little bit forward again. That's basically the effect of the morning light," says Oster.

Our biological clock is located in the brain. Certain cells in the retina react to blue light waves from the sky. This is what Ralph Mistlberger, a psychologist at Simon Fraser University in Burnaby, Canada, explains: "They are specialized in telling the brain whether the sun is shining or not. And so the circadian clock records this light information and adjusts its phase every day."

With this knowledge, Mistlberger took part in a Canadian study. The aim of the research was to find out which time arrangement is healthier for us. The result: Permanent summer time would make the evenings longer, but especially in winter the sunrise would be delayed by another hour.

Mistlberger says: "Sunset - who cares?" The sunrise is crucial. This persistent morning darkness would have noticeable consequences. "Our circadian clocks adjust to the sunrise, and with permanent daylight saving time we will naturally want to stay up later and go to bed later," explains the psychologist.

During the night the clocks were set back by one hour - normal time begins again for chronobiologists. more

However, if everyday life - such as the start of work or school - does not change accordingly, the biological clock shifts backwards. Falling asleep and waking up would be more difficult because the internal clock still signals night. Researchers refer to this phenomenon as “social jet lag,” which can lead to chronic lack of sleep.

Numerous studies show the health consequences of too little sleep: metabolic disorders such as diabetes, cardiovascular problems, high blood pressure and mood disorders can occur. Mental health also suffers from poor sleep and prolonged darkness in the morning.

Winter depression in particular could occur more frequently. Whether this effect would be equally evident with permanent summer time "can of course only be tested in practice. But the evidence is already pretty strong," says Henrik Oster.

Studies also show that there are around ten percent more traffic accidents on the days after the change to summer time in spring. Experiences from the USA and Russia, where permanent summer time was temporarily introduced, show the same picture: both countries abolished it - due to dissatisfaction among the population and an increased accident rate.

Despite strong criticism, the time change remains - because abolishing it would have more consequences, especially for West and East

The Canadian study found that the health benefits of permanent daylight saving time are a third less than permanent standard time, also known as winter time.

In Germany and Europe it applies from October to March. Because it fits our biological clock better, especially because of the morning light. Researchers therefore recommend abolishing the time change entirely and sticking with this standard time. Henrik Oster advises: "If we manage to go out regularly and soak up the sunlight, then I think we're on the right track."

This topic in the program: tagesschau.de | About the time change: Is the morning light crucial? | Oct 22, 2026 | 12:22 p.m