Many people worry that the clocks will go back an hour in winter, but reassure themselves that they will at least get an extra hour of sleep. However, in my new research, my colleagues and I found that most people don’t (or can’t) benefit from the full extra hour of sleep in the fall.

Daylight saving time is the practice of moving the clock forward one hour in the spring and back one hour in the fall. It was introduced during World War I as a way to reduce energy costs. It is active in about 70 countries and affects a quarter of the world’s population.

This “jumping forward” and “falling back” is generally considered a loss of an hour of sleep in the spring and a gain of an hour of sleep in the fall. However, research shows that after both clock changes, we cannot sleep for about a week, as we have difficulty adjusting to the new time.

Previous studies relied on people reporting their own sleep patterns in diaries or surveys. However, this may not be accurate because people sometimes forget or lie about how long they slept. Recent research has solved this problem by using activity monitors that record people’s sleep over clock changes. But so far, researchers have only been able to do this in a small number of people.

Our new study examined the effects of clock changes on objectively measured sleep duration in a large sample of people registered with the UK Biobank. This is a research database containing lifestyle and health information from half a million British participants. We analyzed the sleep data of 11,800 people who wore an activity monitor for one or more days during the two weeks surrounding the spring and autumn clock changes in 2013-2015.

We discovered that people slept more than half an hour longer on the Sunday of the autumn clock change than on the surrounding Sundays. But people slept about an hour less on the Sunday of the spring clock change.

Previous research shows that people sleep less on the weekdays immediately after changing the clock than on the weekdays before. In contrast, this study found that people generally caught up on sleep Monday through Friday after both clock changes. This trend was stronger in the spring after people lost an hour of sleep. On average, people slept seven minutes more per weeknight after the spring clock change and three minutes more per weeknight after the autumn clock change than the week before.

This suggests that the effects of the clock changes on sleep duration are shorter-lived than previous studies reported. However, when we analyzed the data, we found that this pattern of sleep catch-up was not observed in women. In fact, women often slept less on the weekdays after changing their clocks than before. This could be because women are more likely to suffer from insomnia and sleep problems, and these problems are exacerbated by changing the clock. It is believed that women struggle with insomnia more than men for a number of reasons, including hormonal fluctuations, societal factors, and higher rates of depression and anxiety.

We also discovered that elderly and retired people slept less in the autumn on the weekdays after the transition than before. It may be that older people are particularly vulnerable to sleep disruption caused by clock changes, as sleep becomes lighter and more fragmented as we age.

Why does this matter?

Although short-lived, the sleep loss we saw during the spring clock change in our study has health implications, as just one night of poor sleep has been linked to a decline in mental and physical health.

Research has shown that changing the clock itself is associated with an increase in heart attacks, strokes, traffic accidents and depression. Sleep plays a crucial role in keeping your heart healthy and maintaining emotional regulation. The amount of sleep you get also affects your reaction times and how likely you are to take risks.

Concerns about the harmful effects of clock changes on health have prompted sleep scientists to call for the abolition of clock changes. A growing number of countries – including the US, Jordan, Mexico, Ukraine and those in the EU – have made plans to do just that.

But stopping the clock changes isn’t easy. The plans in both the US and EU have stalled, with disagreement over when they should be finally adopted. Sleep experts claim that keeping winter time (standard time) is best for your health because it gives priority to morning light, which wakes you up, resets your biological rhythm every day and makes it easier for you to sleep in the evening to fall asleep. Meanwhile, politicians are campaigning for permanent daylight saving time because of the economic benefits they believe it will bring.

Britain is in an interesting position. Because the country is no longer part of the EU, it is not obliged to stop the clock at the same time as the EU. But being out of sync with the rest of Europe (including the Republic of Ireland) could have economic and logistical consequences.

The British government is likely to review its daylight saving policy once the EU finally puts an end to clock changing. It is crucial that they consider the effects on sleep and health when this happens.