October 25, 2026, 8:37 am | Read time: 6 minutes
Twice a year, the clocks are changed. But what does this actually mean for our bodies? Satchin Panda, a professor at the Salk Institute and one of the world’s leading chronobiologists, has been studying our internal clock and how it reacts to changes in our usual rhythm for years. In an interview with me, he explains the effects that time changes can have on our health, whether daylight saving time or standard time is better for our bodies, and why we tend to make unreasonable decisions in the evening.
FITBOOK: In Europe, the abolition of time changes was partly justified with health benefits. Is this one-hour shift twice a year really that harmful?
Satchin Panda: “Especially in the spring, when the clock is set forward by one hour, we observe an increase in accidents, among other things. But the time change has other consequences. People miss flights or trains, and productivity decreases. Even if someone is only less productive for a single day, it amounts to a productivity loss of about 0.5 percent over the year. At the same time, global productivity has stagnated for about 18 years. So the question is whether we want to accept an additional, actually avoidable loss with the time change.”
In Europe, the abolition of time changes has been discussed for years. However, it is still controversial whether standard time or daylight saving time should apply permanently.
“A particular problem is Spain. If you look at the longitude, the country is actually in the same time zone as the United Kingdom. Nevertheless, Central European Time applies there.”
The reason for this lies in the past: In 1940, the clocks were set forward by one hour under the Franco dictatorship. The change was not reversed after World War II.
“And that’s why Spaniards today generally eat very late.”
Instead of Time Changes! »We Could Theoretically Return to Local Times
As a chronobiologist, what would be the better solution for Europe, standard time or daylight saving time?
“Standard time is the default time, and most people prefer it. Ultimately, we orient ourselves by local solar time, meaning sunrise and sunset. The eastern edges of a time zone have clear advantages because they get the sun earlier. The western edges, on the other hand, suffer because they lag behind. This is the challenge when trying to arbitrarily group large land masses into a single time zone. That’s why I’d like to introduce a completely different idea.”
Which one?
“Humanity has existed for about 140,000 to 200,000 years. We’ve only been experimenting with time zones for about 170 years. They were useful for coordinating industrial processes. Before that, local solar time was used everywhere. So there is still room for improvement. With modern computer technology and AI, we could theoretically return to local solar times while machines handle the necessary coordination.”
Regardless of time zones and clocks, one thing remains undisputed: Life on Earth still largely orients itself by the sun. Is there also a circadian rhythm for human relationships in this dynamic?
“Definitely. As hunters and gatherers, people worked during the day. In the evening, they returned, made a fire, and began to bake or grill. While the food was being prepared, light played a central role. Fire was precious and hard to make. It was not private but communal. People sat together, often with extended family, and spent time together. The fire extended our day. This created a completely new way of life. The day was for work, the night for relaxation and social contacts. This is still deeply ingrained in us today.”
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Satchin Panda: »Unreasonable Decisions Happen More Toward the End of the Day
Why does social closeness tend to occur more in the evening than in the morning?
“Social connectedness is often something irrational and emotional and doesn’t always have a clear reason. In the morning, we are usually more rational and objective, with a stronger ability for self-control and goal-oriented action. As the day progresses, this shifts. We become more irrational, which is needed for social interaction. It relies on many decisions that are not strictly rational: discussing, singing, approaching someone you are attracted to. Even rather unreasonable decisions, such as drinking too much, are part of it. All of this typically happens more toward the end of the day.”
It gives our everyday life a certain something.
“I would say it’s the spice of life. If married couples interacted solely rationally, it would have something robotic about it.”
Speaking of evening and night: Does the moon influence our circadian rhythm?
“It used to. But there are studies showing that the moon’s influence is much less today because we are hardly exposed to moonlight anymore. Artificial light overrides this effect. Before electric lighting, many women had menstrual cycles that were synchronized with either the full moon or the new moon. Full moon nights and the days before were particularly special in the past. One aspect was the light. In a full moon night, less fire was needed, you could stay outside or take a small walk if it was safe. This promoted social activity and made people more emotional and irrational toward the end of the day. Hence the term lunatic.”
About the Person
Satchin Panda is a professor at the Salk Institute in California and is among the world’s leading chronobiologists. He researches how our internal clock affects metabolism and sleep and the role of time-restricted eating (intermittent fasting) for health. Panda is also the author of several books, including “The Circadian Code – Sleep Well, Lose Weight, Be Healthy.”
What do you pay attention to in lighting?
“We generally have very dim lighting, hardly any bright lights. When I need targeted light, I use table or bedside lamps that illuminate the work surface but not my face. This architectural concept is called light layering. You work with indirect light over ceilings or walls and supplement it as needed with so-called task lighting that only illuminates a specific area.”