Every year, when the clocks go back in October, millions of people celebrate an “extra hour” of sleep.
But to what extent does this small shift actually affect our body, our sleep and our mood?
According to experts, the fall transition is much gentler than the spring transition, but it is not completely harmless. The shift subtly disrupts our circadian rhythm, the 24-hour internal clock that regulates sleep, alertness, hormone production and mood.
Understanding circadian rhythms
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The effects of the time change are linked to our circadian rhythms – the 24-hour internal clock that regulates sleep, alertness, hormone production and mood.
“There is a circadian clock in every cell of the body, but there is also a master clock: a group of neurons in the brain that automatically tracks light, dawn, dusk and darkness via signals from the eyes,” Timo Partonen, associate professor of psychiatry at the University of Helsinki, told Euronews Health.
“How well this clock works affects the quality of our sleep and our mood. That’s why it’s so important,” he added.
What is daylight saving time?
Daylight saving time is the practice of moving clocks forward one hour in the spring and back in the fall to extend the length of the day. Most countries in Europe, North America, certain regions of Africa and Asia apply this system.
This year, the clocks will go back on Sunday, October 26.
Although many people welcome the extra hour, change still alters our internal rhythm, and some people feel it more than others.
“In general, despite complaints about darkening evenings, autumn is perceived as less strenuous,” he told Euronews Health Professor Malcolm von Schantz, chronobiologist at the University of Northumbria.
“Those who don’t like the change of autumn mainly complain that it is suddenly dark when they leave work. But there are two reasons for this. First, it simply reflects where we live: at this time of year there are not enough daylight hours for mornings and evenings to be bright. This is not due to the time change, but to geography.”
“Secondly, and less intuitively, morning light is much more important for us from a biological and physiological point of view,” according to Prof Schantz.
Timo Partonen agrees: “The time change in autumn is easier to accept because it gives us an extra hour in the day. The main circadian clock adapts more easily to this new schedule.”
However, he cautions that at first, sleep may not be as restorative as during the summer months.
“There is also the risk that people will not use the extra hour to sleep – instead, they go to bed later and continue to accumulate a sleep deficit. The time change could be an opportunity to make up for lost time, but most people do not take advantage of it,” he adds.
How the time change can affect our body
The spring time change—which causes people to lose an hour of sleep—has been linked to short-term spikes in traffic accidents, sleep loss, and heart attacks (one study cited by the American Heart Foundation found a 24 percent increase in heart attacks the day after the change to daylight saving time).
But the switch to October time may still have more subtle effects.
A 2025 study by Liverpool John Moores University and the University of Oxford found that women were more likely than men to report increased worry, confusion and stress in the days following the time change. Disruptions to children’s routines, such as later bedtimes and difficulty waking up, also contributed to stress within households.
Broader health research suggests that frequent time changes may carry more serious long-term risks.
A recent analysis by Stanford Medicine scientists found that biannual time changes may lead to higher rates of stroke and obesity. The study compared three policies – permanent standard time, permanent daylight saving time and the current semi-annual shift – and concluded that seasonal time changes are the worst option.
By modeling light exposure, circadian alignment and health outcomes in the United States, researchers estimated that adopting permanent standard time could prevent about 300,000 strokes per year and reduce obesity in 2.6 million people. Permanent daylight saving time would achieve about two-thirds of these benefits, according to the research.
How to maintain a regular sleep schedule?
Maintaining a regular sleep schedule is one of the most important – and often overlooked – aspects of our long-term health.
“We know it’s important, and we also know that our bodies can cope with some irregularity. But epidemiological data tells us that it is better to minimize fluctuations for good long-term health,” explained Prof. Schantz.
He described the modern habit of catching up on sleep on weekends – known as “social jet lag” – as biologically disruptive.
“Many of us wake up early during the week and sleep in on the weekend, which means changing time zones on Friday and returning on Monday. This pattern has the same negative long-term effects as frequent exposure to jet lag,” he said.
A study published in the Journal of Epidemiology & Community Health showed that people with irregular sleep-wake cycles had a 26% increased risk of experiencing major cardiovascular events, such as heart attacks and strokes, even if they got the recommended 7 to 9 hours of sleep per night.
Should we rethink summer time?
Many sleep scientists and organizations – including the British Sleep Society, which made an official statement on the subject last year – support abandoning biannual time changes in favor of permanent standard time.
The European Union proposed ending seasonal time changes in 2018, and although the European Parliament supported the principle, member states failed to agree on whether to adopt permanent standard time or daylight saving time.
For now, the clock continues to tick back and forth each year.
Experts agree that using the extra hour for real rest — rather than staying up later — can help ease the transition.
“Sleep early enough,” advises Prof. Partonen.
“If the time change occurs overnight from Saturday to Sunday, go to bed at your usual time – or a little earlier – on Saturday. This way you can use the extra hour to sleep and reduce sleep deprivation.”
