How the clocks going forward affects your health – and what you can do about it

Telegraph

30-03-2025

First devised as a means to save coal during the First World War, daylight saving time is something we Britons have learned to live with. By shifting our clocks an hour forward in spring we get to enjoy an extra hour of summer sunlight in the evenings, and switching them back in autumn helps avoid some of the morning gloom.
However, an increasing body of evidence is beginning to show that, biologically speaking, daylight saving time could be doing us an immense amount of harm.
So, who is most affected when the clocks change – and what can we do to reset effectively?
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How it affects your health?
Who does it affect the most?
What to do about it
FAQs
How it affects your health
'If you think about what our biology needs to do, it has to deliver the right chemicals and hormones in the right concentrations to the right tissues and organs at the right time of day to be able to function,' explains Prof Russell Foster, professor of circadian neuroscience at Oxford University.
The way the body works out when it needs to perform all these actions is with an internal biological clock called the circadian rhythm. Everyone's circadian rhythm is slightly different, but broadly we all follow a pattern which is calibrated by sunlight: when the sun comes up it activates our daytime processes, when it goes down our sleeping processes come online. 'If you don't have that temporal structure, our biology starts to fall apart,' says Prof Foster.
If you've ever felt groggy and slow after experiencing jet lag you'll understand what he's talking about. 'That circadian rhythm is absolutely essential for every aspect of our cognitive, emotional and physiological health. If you're pushing your system outside of its normal range, even by an hour, you're forcing it to function earlier than it would expect to and that can cause problems.' But why does the clocks changing have such an impact on our health? 'The analogy I've often made is that our bodies are a bit like an orchestra,' explains Prof Foster.
'You have all the members of the orchestra all playing together in a symphony but if you disrupt any part of that system, the orchestra just becomes a cacophony of sound. It's the same with our biology.'
Beyond disrupting the body clock, daylight saving time can also affect heart health. In 2014, a study looking at heart attack admissions over three years from the University of Colorado found that the Monday after the clocks move forward in spring saw a 24 per cent spike in heart attacks, whereas on the Tuesday after the clocks fall back in autumn heart attacks went down by 21 per cent.
A follow-up study from the American Heart Association found a similar effect four years later, but this time the increase was seen not just on Monday but all the way to Thursday after the clocks changed. And a 2016 study from the Finnish Cardiac Society showed strokes also increased by eight per cent until the Thursday after the clocks jumped forward.
The fact that the clocks change on a Saturday night into Sunday morning, yet the increase in heart attacks was only observed on Monday, is likely to be relevant, says Dr Oliver Guttmann, consultant cardiologist at The Wellington Hospital, a part of HCA UK.
'The sleep-wake cycle has changed and therefore the body is more stressed, especially at the beginning of the week which most people find stressful anyway,' he says. 'Your nervous system is more on edge so you have an increased risk of getting heart complications.'
In short, Mondays are already stressful and losing an hour of sleep only compounds the issue.
Who does it affect the most?
'If you're relatively healthy and you're not sleep deprived do you need to worry? Probably not,' assures Prof Foster.
'What the heart attacks study illustrates is that people who are already weakened – let's say they already have a heart condition or a metabolic abnormality – become much more vulnerable to circadian rhythm disruption. If your body is chronically tired already then taking away an hour means that you're even more impaired.'
The additional stress can then increase the risk of a heart attack, especially in patients who are already at risk due to having high blood pressure, high cholesterol and diabetes, or who are smokers or overweight.
What to do about it
'You don't have to do the full hour-change in one night,' says Dr Guttmann.
'Rather than waking up an hour earlier, go to bed a little bit earlier, and gradually adjust by 15 minutes or so every day in the lead up to the clocks going forward.'
'Morning light and darker evenings make your body want to get up earlier and go to bed earlier, whereas darker mornings and lighter evenings do the opposite,' adds Prof Foster.
'When the clocks change you get less morning light so it becomes more difficult to sleep in the evenings, so I'd advise people to get out there and get as much morning light as possible to drag your circadian rhythm in the right direction. The studies have shown we get used to the daylight saving time after about a week so I'd be consciously trying to get up early in that first week – not earlier than you would normally, but don't sleep in – get outside and get some sunlight.'
While Dr Guttmann stops short of recommending everyone just take the Monday after the clocks change off ('you might just delay the stress until Tuesday') he advises that people should try to adjust their stress levels. 'Try to have a few less meetings and allow yourself to have an easy morning while you get used to things,' he says.
Additionally, Rhysa Phommachanh, health and personal care specialist at Landys Chemist, advises avoiding caffeine in the evenings so as to not further disrupt your ability to fall asleep at the new time.
Home remedies such as warm milk or chamomile tea might also help to ease the transition into British summer time.
That orchestra analogy might work here too: allow your circadian musicians to spend a bit of time warming up before you force them to play a big symphony.
FAQs
1. When do the clocks go forward?
In the UK, as in most of Europe, the clocks go forward by an hour on the last weekend of March. This year, British Summer Time starts on Sunday March 30 at 1am and marks the end of Greenwich Mean Time.
2. Why do the clocks go forward?
In 1916, during the First World War, Germany first turned their clocks forward as a way of conserving energy. It meant they could use less heat and fewer lights during the brighter evenings. Shortly after, other countries adopted the idea, including the UK, where it was named British Summer Time.