Is the spring clock change actually dangerous?

For the great majority of people it is not. The usual experience is a few days of feeling slightly off and short on sleep. What researchers have found is a small, temporary rise in certain health and safety incidents across whole populations in the days right after the spring change. That is a statistical signal spread over millions of people, not a warning that any one individual is at serious risk. It is a reason to be a little kinder to yourself that week, and to avoid driving tired, rather than a reason to worry.

Why is “fall back” in autumn easier than “spring forward”?

Because gaining an hour is gentler on the body than losing one. In autumn you get an extra hour of sleep, and your internal clock shifts in the direction it tends to drift naturally anyway, so most people adjust within a day or two. The spring change takes an hour of sleep away and asks the body clock to jump forward, against its grain, which is why spring is the transition associated with the short-term effects researchers have measured.

If the clock change is abolished, is permanent summer time or permanent standard time better?

Many sleep scientists favour permanent standard time, because it keeps sunrise closer to when people wake, and morning light is the strongest signal for keeping the body clock aligned. Permanent daylight saving gives lighter evenings but very dark winter mornings, which works against the circadian clock. The lighter-evening option is often more popular politically, so which one a country lands on is not settled by the science alone.

Guide

Daylight saving time and your health

By Nicolai Lykke 21 September 2026

Twice a year most of Europe and North America move their clocks by an hour, and the two moves are not equal. The autumn change hands an hour back and is barely noticed. The spring change takes one away, and for a few days afterwards a fair amount of evidence suggests it leaves a mark, on sleep, on mood, and on a scattering of health and safety statistics. None of this makes the clock change a catastrophe. But it is not quite the non-event it is often treated as either, and it is worth understanding why the lost hour lands harder than the arithmetic implies.

The lost hour and the body clock

When the clocks go forward you do not simply lose an hour on paper. Your body runs on a circadian rhythm, an internal clock, close to twenty-four hours long, that governs sleep, alertness, body temperature and the timing of certain hormones. It is set largely by daylight. Spring forward means the clock on the wall now reads an hour ahead of where your body still is: your alarm, your commute and the sunrise all shift, but your internal timing takes several days to catch up. Until it does, you are being asked to wake and work while your body still thinks it is an hour earlier.

This is a mild, one-hour version of the same misalignment behind jet lag, except that you have not gone anywhere. That is part of what makes it sneaky. A traveller expects to feel out of step and plans around it; the clock-change version arrives on an ordinary Monday, unannounced, and on top of a night that was simply an hour shorter. Even good sleepers tend to get less sleep in the days after the spring change, and the deficit takes a while to repay.

What researchers have found

Researchers who have looked at the days immediately after the spring change have reported small, short-term increases in several things you would rather not increase: heart attacks, strokes and traffic accidents. The direction of the effect is reasonably well documented across different countries and datasets. What is far less settled is the size: estimates vary from study to study, some findings are debated, and this is a field where it is easy to over-read a noisy statistic. The honest summary is that there appears to be a real but transient bump in the first few days, which fades as people readjust, rather than any lasting change in risk.

As one illustration of the scale people have reported, one study found roughly a quarter more heart attacks on the Monday following the spring change. That is a single study's finding rather than a settled figure, and it is best read as a hint about direction and rough order of magnitude, not a precise measure of anyone's risk. The autumn change points the other way: gaining an hour of sleep is easier on the body, and the “fall back” transition is generally associated with milder effects, sometimes even a small dip in the same incidents.

Why morning light matters

The debate about scrapping the clock change usually splits into two camps: permanent daylight saving, for lighter evenings all year, and permanent standard time. It is worth knowing that most sleep scientists come down on the side of standard time, and the reason is morning light. The circadian clock is anchored most strongly by light early in the day; morning daylight is what keeps your internal timing lined up with the solar day. Permanent daylight saving would push winter sunrises very late in many places, people waking, commuting and starting school in the dark for months, which is exactly the condition that lets the body clock drift out of alignment.

Permanent standard time keeps the sun coming up nearer to when people actually get up, which is why many sleep-medicine bodies, asked to choose, favour it over the lighter-evenings option that tends to be more popular at the ballot box. Which system a country picks, of course, is a separate and very political question, the politics of daylight saving and the state of the effort to stop changing the clocks are their own long stories, and the science is only one voice in them.

How to soften the change

If the spring change tends to leave you groggy, the tactics that help with mild jet lag help here too, and they are worth starting before the clocks move rather than after. Instead of absorbing the whole hour on Sunday night, shift your sleep and wake times earlier by fifteen or twenty minutes a day over the several days beforehand, so that by the time the clocks jump your body is already partway there. Then, on the morning after the change, get outside into daylight early, that morning light is the strongest signal for pulling your internal clock forward to meet the new schedule.

For the surrounding days, the sensible thing is simply not to run on empty. The week of the spring change is not the one to skimp on sleep, drive tired or schedule something that leaves no margin for feeling below par. For most people none of this is a big deal. The spring change is a few days of mild grogginess and no more. If you want to see exactly which places are shifting their clocks, and how the gap to another city moves as a result, the daylight saving tracker keeps up with it. Knowing why the lost hour bites, and nudging your own clock ahead of it, is usually enough to take the edge off.

Is the spring clock change actually dangerous?: For the great majority of people it is not. The usual experience is a few days of feeling slightly off and short on sleep. What researchers have found is a small, temporary rise in certain health and safety incidents across whole populations in the days right after the spring change. That is a statistical signal spread over millions of people, not a warning that any one individual is at serious risk. It is a reason to be a little kinder to yourself that week, and to avoid driving tired, rather than a reason to worry.
Why is “fall back” in autumn easier than “spring forward”?: Because gaining an hour is gentler on the body than losing one. In autumn you get an extra hour of sleep, and your internal clock shifts in the direction it tends to drift naturally anyway, so most people adjust within a day or two. The spring change takes an hour of sleep away and asks the body clock to jump forward, against its grain, which is why spring is the transition associated with the short-term effects researchers have measured.
If the clock change is abolished, is permanent summer time or permanent standard time better?: Many sleep scientists favour permanent standard time, because it keeps sunrise closer to when people wake, and morning light is the strongest signal for keeping the body clock aligned. Permanent daylight saving gives lighter evenings but very dark winter mornings, which works against the circadian clock. The lighter-evening option is often more popular politically, so which one a country lands on is not settled by the science alone.