Will you get an extra hour of sleep this weekend? Probably not, new research says

Many people fear that the clocks will go back an hour in the winter – but they can rest assured that they will at least get an hour more sleep. However, in my new study, my colleagues and I found that most people don't use (or can't use) the full extra hour of sleep in the fall.

During daylight saving time, the clocks are set forward one hour in spring and set back one hour in autumn. It was introduced during World War I to reduce energy costs. It is common in around 70 countries and affects a quarter of the world's population.

This “jumping forward” and “falling back” is generally viewed as one hour of sleep lost in the spring and one hour of sleep gained in the fall. However, research suggests that after both time changes, we may not be able to sleep for about a week as we struggle to adjust to the new time.

Previous studies have relied on people reporting their own sleep patterns in diaries or surveys. However, this may not be accurate as people sometimes forget or lie about how long they slept. Recent research has solved this problem by using activity monitors to record people's sleep across time changes. But so far researchers have only succeeded in doing this with a small number of people.

Our new study examined the effects of clock changes on objectively measured sleep duration in a large number of people enrolled in the UK Biobank. This is a research database containing lifestyle and health information from half a million UK participants. We analyzed sleep data from 11,800 people who wore activity monitors for one or more days in the two weeks surrounding the time change in the spring and fall of 2013-2015.

We found that people slept a little over half an hour more on the Sunday of the fall time change than on the surrounding Sundays. But on the Sunday of the time change in spring, people slept around an hour less.

Previous research suggests that people sleep less on the weekdays immediately after the time change than on the weekdays before. In contrast, this study found that overall, people caught up Monday through Friday after both time changes. This trend increased in the spring after people lost an hour of sleep. On average, people slept seven minutes more per week after the spring time change and three minutes more per week after the fall time change than in the previous week.

This suggests that the effects of clock change on sleep duration are shorter than reported in previous studies. However, when we broke down the data, we found that this pattern of catching up on sleep was not observed in women. In fact, women often slept less on weekdays after the time change than before. This could be because women are more likely to suffer from insomnia and sleep disorders and these problems are made worse by the time change. Women are thought to struggle more with insomnia than men due to a variety of reasons, including hormonal fluctuations, societal factors, and higher rates of depression and anxiety.

We also found that older people and pensioners slept less on weekdays in the fall after reunification than before. It may be that older people are particularly vulnerable to having their sleep disrupted by the time change, as sleep becomes lighter and more fragmented as we age.

Why is this important?

The sleep loss observed in our study during the spring time change is short-lived but has health implications, as even a single night of poor sleep has been linked to worsening mental and physical health.

Research has found that the clock changes themselves are linked to an increase in heart attacks, strokes, traffic accidents and depression. Sleep plays an important role in maintaining heart health and emotional regulation. The amount of sleep you get also affects your reaction times and the likelihood of you taking risks.

Concerns about the harmful effects of the time change on health have led sleep scientists to call for the time change to be abolished. In fact, a growing number of countries – including the US, Jordan, Mexico, Ukraine and the EU – have planned to do just that.

However, stopping the time change is not easy. Plans have stalled in both the US and EU, and there is disagreement over when permanent implementation should take place. Sleep experts argue that sticking to winter time (standard time) is best for your health because it emphasizes morning light, which helps you wake up, reset your biological rhythm each day, and helps you fall asleep relieved in the evening. Meanwhile, politicians are pushing for permanent daylight saving time because they believe it has economic benefits.

Britain is in an interesting position. Since the country is no longer part of the EU, it is not obliged to stop the time change at the same time as the EU. But a deviation from the rest of Europe (including the Republic of Ireland) could have economic and logistical implications.

The UK government is likely to review its summer time policy once the EU finally ends the time change. It is important to consider the effects on sleep and health.