How to prepare your sleep when your schedule changes

Why your body finds it hard to change schedules

The body has its own clock that sets, among other things, when you feel sleepy and when you're most alert. Its cycle lasts a little over 24 hours and is reset every day by signals from outside, above all light. That reset isn't immediate: when your schedule changes suddenly, the clock keeps the old time for a while, and that mismatch is where sleepiness at odd hours and nights when it's hard to fall asleep come from.¹⁰

Light doesn't always push in the same direction. Broadly speaking, light that arrives at the end of the day and early in the night moves the clock later, and light that arrives at the end of the night and in the morning moves it earlier.¹⁰ We explain why it works this way, and what light is best during the day, in daylight and sleep.

Two more details. First: because the clock's cycle lasts a little over 24 hours, it tends to move later more easily than earlier, and traveling east, which forces it earlier, is usually harder than traveling west.⁹¹⁰ Second: in the two or three hours before your usual bedtime, it's especially hard to fall asleep. This was described in 1986 in a laboratory experiment with adult men, and it has been called the “forbidden zone for sleep.”¹¹ Our inference: that's why going to bed three hours earlier than usual the night before an early start rarely works.

The clock change: when it happens in Spain and what has been observed

Throughout Spain except the Canary Islands, on the last Sunday of March 2:00 a.m. becomes 3:00 a.m., and on the last Sunday of October 3:00 a.m. goes back to being 2:00 a.m. In the Canary Islands the change takes place at 1:00 a.m. in March and at 2:00 a.m. in October.¹

A 2013 review suggests that the spring change isn't just the hour lost that night: sleep is more disrupted and falling asleep is harder, with a loss that builds up over at least the following week. It also suggests there's little evidence that people sleep an extra hour on the night of the autumn change.² Some specific studies:

• Adults in Finland. Nine healthy adults aged 20 to 40 wore a wrist sensor around both changes. After both, their nights were more restless, and four days later the adjustment still wasn't complete. The spring change had more effect on people who tended to go to bed late, and the autumn change on those who tended to get up early.³
• Students in the United States. The 35 high school students in New York State who wore a wrist sensor slept on average 32 minutes less per night in the week after the spring change than in the week before, were sleepier during the day and responded more slowly on an attention test.⁴
• Traffic. In US records of fatal traffic accidents between 1996 and 2017 (732,835 accidents), the risk rose by 6% after the spring change, especially in the morning, and the increase faded over the following week; it wasn't seen with the autumn change.⁵

The Sociedad Española de Sueño (Spanish Sleep Society), which points out that the body clock takes several days to readjust, and the American Academy of Sleep Medicine call for an end to changing the clocks and for staying on standard time, winter time, all year round.⁷⁶

How to prepare for the clock change

For the March change, the American Academy of Sleep Medicine advised in a 2013 note going to bed 15 or 20 minutes earlier each night in the days before, also moving earlier other routines that mark out the day, such as dinner, and getting out into early-morning light on the Sunday.⁸ It's advice from a medical society; we haven't found trials that have compared it with doing nothing at the clock change.

There is, however, an experiment on the same idea, designed for eastward travel: 28 healthy adults moved their sleep schedule an hour earlier each day for three days, with different light in the morning. The chart shows how far their clock moved earlier. The sleep loss was small, less than an hour on average, and was concentrated in the first night.⁹

For the October change there's less sourced advice. The clock has to move later, which is generally easier for it,¹⁰ but in the Finnish study this change had more effect on people who tended to get up early.³ Our inference: if you're one of those people, you can move your bedtime a little later in the days before and seek out light in the early evening, which pushes the clock later;¹⁰ and, from Sunday, get up at your usual time by the new clock.

After the March change, if you drive while sleepy, take extra care: the American Academy of Sleep Medicine advised this for that Sunday,⁸ and the rise in accidents was seen in the following days.⁵

Travel across time zones

Jet lag appears in the days after a trip that crosses several time zones, usually more than three,¹² because the body clock stays on the time of the place you left;¹⁰ it usually improves within a few days.¹³

What you notice depends on the direction. After a long trip west, your body wants to sleep in the early evening and wakes up too early. After one east, it's hard to fall asleep at bedtime and sleepiness appears in mid-morning or early afternoon.¹⁰

• Before you leave. The US CDC suggests starting to adjust your schedule a few days in advance: going to bed one or two hours later than usual if you're traveling west, and one or two hours earlier if you're traveling east. And, if you can, arriving at least two days before anything important.¹² An opinion article proposes steps of 30 to 60 minutes a day for three or four days, with light in the morning if you're heading east and in the evening if you're heading west.¹⁰
• During the trip. The UK's NHS advises drinking water, moving around the cabin, trying to sleep if it's night at your destination and not overdoing caffeine or alcohol.¹³
• On arrival. Switch as soon as possible to your destination's times for sleeping and waking up, and get out into daylight.¹³¹² On naps the sources disagree: the NHS advises sleeping only at night,¹³ and the CDC allows short naps, of 15 to 20 minutes at most.¹² More on how long they should last and when in the article on naps.
• Short trips. If you'll only be away for two or three days, the NHS suggests trying to keep to your home schedule, so you don't have to change it again when you get back.¹³

A nuance about light, from the same opinion article: after a long trip west, daylight at your destination helps the clock move later; after one east, early-morning light in the first few days can push it in the opposite direction. For eight hours east, the authors propose avoiding bright light before midday and seeking it out in the hours after. They base this on laboratory experiments, and acknowledge that studies with real travelers are few and their results mixed.¹⁰

A one-off early start or a period on a different schedule

For an early start on a single day, the body clock doesn't need to change: the problem is sleeping less that night. Going to bed much earlier than usual has a limit: those hours fall in the zone where it's hardest to fall asleep.¹¹ Our inferences:

• If you know a few days ahead, move your schedule earlier in steps of 15 to 30 minutes and seek out light in the morning, the same logic as in the three-day experiment.⁹
• If there's no time to prepare, go to bed a little earlier, without forcing it, and accept that the night will be shorter. The next day, go back to your usual schedule instead of catching up all at once; if you need a nap, a short one, not too late in the day, is better.

A period on a different schedule—summer working hours with an early finish, a temporary job with a different start time, a few weeks of exams—is more like a slow trip than an early start. Our inference: move in steps, in whichever direction applies; pay attention to when you get light, as we saw at the start; and don't let the time you get up on your days off drift far from the new one, so you don't undo the adjustment every weekend with social jet lag. When the period ends, go back the same way, in steps.

To see how you're adapting, it helps to note down for a few days what time you go to bed, how long it takes you to fall asleep and how you feel when you get up; for that, there's a sleep diary template ready to copy.

Shift work and when to see a professional

Working nights or rotating shifts means changing schedules again and again, sometimes every few days. It's a different situation from the ones in this article, and here we don't give guidance on how to organize it.

Spain's Workers' Statute (Estatuto de los Trabajadores) considers night work to be work done between 10 p.m. and 6 a.m., and a night worker to be someone who normally does at least three hours of their daily working time in that period, or who is expected to do at least a third of their annual working time in it. It requires the employer to guarantee these people a free health assessment before they start and then at regular intervals, under the terms of the occupational risk prevention law.¹⁴ Our suggestion: if shifts are affecting your sleep, raise it with your company's risk prevention or occupational health service and with your health professional.

Outside of shift work, if difficulty sleeping or daytime sleepiness lasts for weeks, or affects your daily life, consult a health professional; in the general article we explain when habits aren't enough.