Clocks Go Back: How Daylight Saving Time Affects Your Health

As clocks prepare to fall back this Sunday, October 26, millions across Europe and North America will gain an extra hour of sleep. While this autumn ritual seems like a welcome gift, the twice-yearly clock changes continue to spark debate among health experts, politicians, and citizens who question whether this century-old practice still serves us well.

The Origins of Daylight Saving Time

The concept of daylight saving wasn't born in government chambers but on the back of a horse. In 1907, William Willett, a wealthy builder from Kent, England, noticed during his early morning rides that most people kept their curtains drawn, shutting out precious morning sunlight while they slept. His pamphlet, "The Waste of Daylight," argued that advancing sunrise times would increase recreational daylight hours for workers and reduce home lighting costs.

Though Willett died in 1915 without seeing his idea implemented, World War I changed everything. In 1916, Germany became the first country to adopt daylight saving time to conserve coal, with Britain following weeks later. Today, around 70 countries representing over a quarter of the world's population observe this practice.

The Health Impacts: Spring vs. Autumn

Research consistently shows that the two clock changes affect our bodies very differently. The spring transition—when we "spring forward" and lose an hour—has been linked to serious health concerns.

The Spring Change: A Health Hazard

Studies across multiple countries have documented alarming patterns following the March clock change. Research from the US, Sweden, Croatia, Germany, Brazil, Finland, and Mexico has found that hospital admissions for heart attacks increase by an average of 4% in the days following the spring transition. Fatal car accidents rise by 6% as sleep-deprived drivers struggle with their disrupted schedules.

"Because then you'll have people who are being asked to live their lives against the clock," explains David Ray, professor of endocrinology at the University of Oxford. "Their internal clock tells them it's 7am, but the clock on the wall says it's 6am so they're one hour misaligned. Even one hour carries a certain risk, and of course, if you do it to a whole population, you'll be dialling up quite a lot of disease that is completely avoidable."

The spring change has also been associated with increased rates of stroke, depression, anxiety, and substance abuse, according to a 2020 study.

The Autumn Shift: Milder but Not Harmless

"Generally speaking, despite complaints about evenings getting darker, the autumn one is usually perceived as less painful," says Professor Malcolm von Schantz, a chronobiologist at Northumbria University. The body finds it easier to adjust when gaining an hour rather than losing one.

However, the October change isn't entirely benign. 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 following the autumn clock change. Disruptions to children's routines—later bedtimes and difficulty waking—also contributed to household stress.

Perhaps most concerning, people don't actually use the extra hour for sleep. "There's also the risk that people don't use the extra hour for sleep—instead, they stay up later and continue to build sleep debt," warns Dr. Timo Partonen, associate professor of psychiatry at the University of Helsinki.

Understanding Your Circadian Rhythm

The effects of clock changes stem from disruptions to our circadian rhythms—the body's internal 24-hour clock that regulates sleep, alertness, hormone production, and mood.

"There's a circadian clock in every cell of the body, but there's also a principal clock: a group of neurons in the brain that automatically follows light, dawn, dusk, and darkness via signals from the eyes," Partonen explains. "How well this clock functions affects how well we sleep and how good or bad our mood is."

At night, falling light levels trigger the brain's pineal gland to produce melatonin, making us sleepy. Morning light stops melatonin production and releases cortisol, promoting wakefulness. The spring clock change disrupts this finely tuned system by adding evening light when we should be winding down and keeping mornings darker when we need to wake.

Long-Term Health Consequences

Recent research suggests the biannual clock shifts may carry more serious long-term risks than previously understood. A Stanford Medicine analysis found that seasonal time changes are associated with higher rates of stroke and obesity compared to permanent standard time or permanent daylight saving time.

By modeling light exposure and circadian alignment across the United States, researchers estimated that adopting permanent standard time could prevent approximately 300,000 strokes annually and reduce obesity in 2.6 million people.

The disruption resembles what researchers call "social jet lag"—the modern habit of sleeping in on weekends after waking early all week. "That pattern has the same long-term negative effects as frequent exposure to jet lag," von Schantz notes.

A study in the Journal of Epidemiology & Community Health found that individuals with irregular sleep-wake cycles had a 26% higher risk of major cardiovascular events like heart attacks and strokes, even when getting the recommended 7-9 hours of sleep.

The Political Stalemate

Despite growing evidence of health harms, efforts to end clock changes have stalled. The European Parliament voted to abolish the practice in 2019, giving member states until the end of 2021 to decide whether to remain on permanent summer time or winter time. However, countries couldn't reach consensus, and the plan remains indefinitely postponed.

Spain's Prime Minister Pedro Sanchez has emerged as a vocal opponent, recently taking to social media to argue that "changing the time twice a year no longer makes sense. It barely helps save energy and has a negative effect on people's health and lives." Spain's energy ministers have joined colleagues from Finland and Poland in pushing for change.

In a YouGov poll from October 2024, 59% of Britons said they would prefer permanent summer time if the current system were scrapped, though health experts generally recommend permanent standard time instead.

Expert Tips for Managing the Transition

Until policy changes, health experts offer practical advice for minimizing disruption:

Use the Extra Hour Wisely

"Go to sleep early enough," advises Dr. Partonen. "If the clock change happens on the night between Saturday and Sunday, go to bed at your usual time—or slightly earlier—on Saturday. That way, you can use the extra hour for sleep and reduce any sleep deprivation."

Prioritize Morning Light

"Biologically and physiologically, light in the morning is much more important for us," von Schantz emphasizes. Getting bright light exposure early in the day helps reset your circadian clock and improves sleep quality.

Maintain Consistency

"For long-term health it's better to minimise fluctuations," says von Schantz. Try to keep your sleep schedule as regular as possible throughout the week, even on weekends.

The Case for Permanent Standard Time

Many sleep scientists and organizations, including the British Sleep Society, support ending biannual clock changes in favor of permanent standard time. This would keep clocks aligned with the sun's natural cycle, providing more morning light when our bodies need it most for circadian regulation.

The debate highlights a fundamental tension: while many people enjoy lighter summer evenings, "at that time of year, there aren't enough daylight hours to keep both mornings and evenings bright," von Schantz points out. "That's not a result of the clock change, just geography."

Conclusion: Time for Change?

As we prepare to set our clocks back this Sunday, the mounting evidence suggests William Willett's century-old idea may have outlived its usefulness. While the autumn transition causes fewer immediate problems than its spring counterpart, the biannual disruption to our circadian rhythms carries measurable health costs—from increased cardiovascular events to heightened stress and mood disturbances.

Whether Europe and other regions will finally abandon this practice remains uncertain. For now, the best approach is to treat the clock change mindfully: go to bed on time, seek morning light, and use that extra hour for actual rest rather than late-night scrolling. Your body—and your heart—will thank you.