Daylight saving time and your sleep: why the spring change hurts, and a four-day plan

What the clock change does

Your body clock does not read the wall clock; it reads light. When clocks move forward in spring, sunrise suddenly comes an hour later by the clock, so the morning light that would normally pull your body clock earlier arrives late. Your internal time lags social time — like a one-hour eastward flight you never took — and for many people it takes a week or more to settle. The autumn change goes the other way and most people adjust within a day or two.

What the research shows

The effects are small at the level of one person and measurable at the level of a country. An analysis of 732,000 fatal road crashes in the United States over 22 years found about a 6% rise in the week after the spring change, concentrated in the mornings and larger in the western part of each time zone, where the sun rises later by the clock. A Swedish registry study found that heart attacks were about 5% more common in the first three weekdays after the spring shift, and slightly less common after the autumn shift. These are observational associations, not proof that the clock change alone caused each event, but they are consistent with a population that is briefly sleep-deprived and out of phase — and they are why the American Academy of Sleep Medicine’s 2020 position statement concluded that a fixed, year-round standard time best matches human biology and public health.

The policy detail matters: the statement favours permanent standard time, not permanent daylight time. Permanent daylight time would mean dark winter mornings across much of North America and Europe, and morning light is what the body clock needs most. Until policy changes, preparation is the practical answer.

The four-day plan for spring

1. Four nights before: go to bed and wake 15 minutes earlier than usual.
2. Each following night: another 15 minutes, so that by the change you have moved a full hour.
3. Move meals and exercise earlier by the same amount; they are secondary clock signals.
4. On the morning after: get outdoor light as early as you can. Keep evenings dim.

Children

Young children run on routine and cannot be talked into feeling sleepy an hour early. Shift the whole evening — dinner, bath, story, lights out — by 10 to 15 minutes a night over the week before, keep the room dark in the morning until the new wake time, and get them outside soon after waking on the days after. Expect a few crankier afternoons; it passes within a week or two.

Older adults

Body clocks tend to run earlier with age, and sleep becomes lighter, so the spring change often means early waking plus an evening that suddenly feels late. The same rules apply — morning light, a fixed wake time, dim evenings — with one addition: be deliberate about outdoor light in the afternoon too, because a strong day–night contrast steadies an older clock more than either half alone.

If you drive for a living or work shifts

The week after the spring change is the one in which to be strict about the rules you already know: no drowsy driving, a short nap before a night shift, caffeine early in the shift rather than late. If your roster changes at the same time as the clocks, treat the two together and protect the anchor sleep described in the shift-work guide.

The autumn change

Falling back gives most people an easier night: the clock asks you to stay up later, which the body clock finds easy, and there is an extra hour in bed. It is not entirely free. Sunset jumps an hour earlier overnight, so a commute that was in daylight is suddenly in the dark, and for people prone to low mood in winter this is often the week it starts. The two mistakes to avoid are sleeping in on the Sunday (which wastes the easy adjustment) and letting bedtime drift later over the following week (which turns a one-hour gain into a one-hour loss). Keep your wake time steady by the new clock, get morning light, and make the evening deliberately bright until 8 or 9 pm; the extra evening darkness is the start of the winter pattern described in winter darkness and your sleep.

Who doesn’t change clocks

Queensland and Western Australia stay on standard time all year, which is why Brisbane and Perth have sunrise around 5 am in summer. Most of Saskatchewan, Arizona (outside the Navajo Nation) and Hawaii do the same. Their sleep issue is early summer light, not the change itself.

In summary

The spring clock change is a one-hour eastward flight for everyone at once. Pre-shift over four nights, use morning light afterwards, keep evenings dim, and be careful on the roads that week.