Some links on this page may be affiliate links. If you purchase through them, we may earn a commission at no extra cost to you.

Written by

Syed Hammad

Author

Hammad is a researcher studying the molecular blueprint of the focusing system in eye. Hammad spends his days looking through a microscope and free time thinking about the details of anything—and everything—in between.

KEY TAKEAWAYS

Daylight Saving Time (DST) disrupts the body's circadian rhythm, causing sleep disturbances and reduced cognitive function immediately after the clock change.
The population-wide misalignment from DST leads to measurable increases in traffic accidents and cardiac events shortly after the spring forward transition.
The original energy-saving rationale for DST is outdated and largely unsupported by modern research, especially in warmer regions where air conditioning use offsets any lighting savings.
Economic interests such as retail, sports, and tourism benefit from longer evening daylight, influencing the persistence of DST despite its physiological costs.
There is ongoing political debate about abolishing or modifying DST, with some advocating for permanent Standard Time to better align with natural circadian rhythms.

GLOSSARY

Daylight Saving Time (DST)

A practice of setting clocks forward by one hour in spring and back in autumn to extend evening daylight, originally intended to save fuel during wartime.

Circadian Rhythm

The body's internal clock regulating sleep, hormone release, and other physiological processes, which is disrupted by the sudden time shift of DST.

Spring Forward

The act of moving clocks one hour ahead in March, resulting in the loss of one hour of sleep and causing temporary biological misalignment.

Standard Time

The time zone aligned with the sun's actual position, considered by some experts to better support natural circadian rhythms than DST.

Bi-annual Shift

The twice-yearly adjustment of clocks forward in spring and backward in autumn as part of the DST system.

Physiological Stress

The bodily strain caused by having to function earlier than the circadian rhythm is ready, linked to increased cardiac events after DST changes.

FAQ

Why does Daylight Saving Time disrupt sleep and body functions?

DST shifts the clock forward by one hour suddenly, but the body's circadian rhythm does not adjust immediately. This causes misalignment between internal biological time and external schedules, leading to disturbed sleep, altered appetite, and mood changes.

What are the broader consequences of the population waking up out of sync after DST changes?

When an entire population experiences circadian misalignment simultaneously, it results in increased risks such as more traffic accidents and a rise in cardiac events. These effects are most pronounced in the days immediately following the spring forward transition.

Does Daylight Saving Time still save energy as originally intended?

Modern research indicates that DST no longer provides meaningful energy savings. In some regions, especially warmer climates, increased use of air conditioning during longer evenings cancels out any reduction in lighting use.

Who benefits economically from maintaining Daylight Saving Time?

Industries like retail, sports, leisure, tourism, and outdoor venues benefit from longer evening daylight, as it encourages more consumer activity and extends business hours, providing a financial incentive to keep DST.

What are the current political debates surrounding Daylight Saving Time in the UK?

Parliament is divided, with some members advocating for abolishing the bi-annual clock changes, others proposing an additional hour advance in Summer Time, and groups like the British Sleep Society recommending permanent Standard Time to better align with natural circadian rhythms.

EDITORIAL NOTE

This piece is part of The Present Minds — essays on psychology, identity, and modern life.

Tap to switch read mode. Original contrast is live.

How daylight saving time affects body and sleep is a question most people answer with a shrug and a second coffee. The biology underneath that shrug is more interesting than they think.

At 1 a.m. on Sunday, 29th March 2026, I was robbed. No broken window, no barging through the doors. Just silence, and an hour cleanly swept from my clock.

I was not alone. It happened across the country, all at once.

We call it Daylight Saving Time. A term I find amusing because, for anyone fighting for an extra five minutes of sleep, it feels less like a saving and more like a theft. It was first staged in 1916 to save fuel and make better use of daylight during the First World War.

With a few exceptions, it has remained in place ever since. Spring forward in March, fall back in October. What is taken in March gets returned in October. A perfect balance, so they say.

The balance is not quite as perfect as it sounds.

The body that did not get the memo

The Monday after the clocks change has a specific quality. A lag. Slower thinking, slipping concentration, an extra cup of coffee that barely touches it. The world feels slightly out of sync.

That is because it is.

We have a timekeeping system in our body called the circadian rhythm. It is guided by hormones, sunlight, and sleep patterns. Our alarms and schedules provide external cues to keep it calibrated. When the clock shifts forward, the circadian rhythm does not follow.

The body is suddenly expected to function an hour earlier than it is ready to. Sleep patterns get disturbed, appetite shifts, mood takes a hit. Some people adjust in a few days. Others take weeks. Those with rigid schedules feel it more sharply than those with flexibility. The body adapts, but not without cost.

When a population wakes up out of sync

An hour of misalignment does not sound like much. Scaled to an entire population waking up out of sync at the same time, it becomes measurable.

A study at the University of Surrey found that the disruption to the circadian rhythm following the spring forward transition leads to drivers taking more risks and misjudging situations, producing a rise in traffic accidents in the days immediately after the clocks change.

The risk fades as the season progresses and the body adjusts. The window is narrow, but real.

The heart also feels it. Several studies report a rise in cardiac events in the days after the clock change, likely due to the physiological stress of performing before the body is properly ready. The stress is quiet. The consequences are not always.

How daylight saving time affects body and sleep and who profits from it

The closer you look at how daylight saving time affects your body and sleep, the harder it is to ignore the question of who actually benefits from keeping it.

Retailers benefit. Sports and leisure businesses benefit. Golf courses fill up. Garden centres, shopping centres, and outdoor venues see more footfall. Tourism extends its season.

The longer evenings are worth real money, and the industries that depend on them have lobbied hard to keep the arrangement in place. For them, the hour is not stolen. It is redistributed somewhere they prefer.

The original justification was energy conservation. The world of 1916 looked nothing like the one we live in now. Modern research has largely failed to confirm any meaningful energy saving in contemporary conditions.

In some warmer regions, longer evenings increase air conditioning use, cancelling out whatever is saved by not switching on the lights an hour earlier. The premise did not age well. It survived anyway.

The question parliament has not answered

Parliament is currently divided on what to do.

Some MPs want to scrap the bi-annual shift altogether. Others want to advance Summer Time by an additional hour. The British Sleep Society advocates for keeping Standard Time year-round, arguing it reflects the sun’s actual position and aligns better with the circadian rhythm.

No decision has been reached. The debate continues at the pace of debates that affect everyone and inconvenience no one with enough power to force a resolution.

Until that changes, the clock will shift again in October. The hour will be returned. Balance technically restored.

The body will adjust. The Monday will pass. The coffee will work again by Wednesday. We stop noticing within a fortnight, which is perhaps the cleverest thing about the arrangement. It is just disruptive enough to feel wrong, and just brief enough to be forgotten before it matters.

Until the following March, when the robbery happens again.

Quietly. At 1 a.m. While everyone is asleep.

What I learnt from a cab driver in london

Why are human babies so helpless at birth?