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.
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