On Sunday, 30 March, clocks in the UK went forward an hour – marking the beginning of Daylight Saving Time (DST), commonly referred to as British Summer Time (BST). DST is a long-standing practice that was first introduced in 1916, intended to make better use of extended daylight hours during the summer months.
However, scientists warn that changing the clocks, particularly the Spring leap forward, is harming our bodies. Expert in circadian rhythms, Dr Jeffrey Kelu, from the Faculty of Life Sciences and Medicine at King’s College London, is exploring this issue.
Why do clock changes impact our health?
Dr Kelu said: “There’s increasing evidence to show that shifting the clocks, particularly in spring, has a significant impact on circadian rhythms and sleep health. Our internal body clocks, synchronised mainly by light exposure, regulate essential physiological functions, such as the sleep-wake cycle and metabolism. Shifting the clock time by one hour creates a misalignment between social time and the natural light-dark cycle, disrupting circadian rhythms.
“The acute effect of the spring clock change is a sudden reduction in sleep duration, caused by the overnight loss of one hour, and the difficulty in adapting to earlier wake times. This can lead to chronic ‘circadian misalignment’, a condition known as ‘social jet lag’, which is associated with an increased risk of obesity, metabolic syndrome, and mood disorders.”
What do scientists think about clock changes?
“Experts in sleep and circadian biology are largely united in their opposition to DST. Multiple international societies, including the British Sleep Society, have issued position statements against the practice, citing its adverse effects on health.
“Following careful evaluation of the scientific evidence, these societies strongly recommend that biannual clock changes be abolished, not only in the UK, but worldwide, wherever DST remains in practice, to safeguard public health and wellbeing.”
What do experts believe would be the best approach?
“In considering which permanent time setting would best support health, these societies strongly endorse a return to permanent Standard Time (equivalent to Greenwich Mean Time, GMT, in the UK), while advising against the adoption of permanent DST.
“Standard Time aligns optimally with human circadian biology by ensuring greater exposure to natural morning light, which is essential for aligning our bodies with the 24-hour clock. This is particularly important in modern societies, where prolonged indoor activity and evening exposure to artificial light tend to delay circadian rhythms, including sleep onset and natural waking. Morning light counteracts this delay, helping to maintain synchrony with the 24-hour day and supporting timely sleep and wakefulness.
“Scientists believe that adopting permanent Standard Time and ending biannual clock changes would promote healthier sleep, improved wellbeing, and better public health outcomes across the UK, and beyond.”
Why would permanently switching to GMT be better than DST?
“Adopting permanent DST, especially during winter, poses risks to sleep and health worldwide by reducing morning light exposure. Morning light is essential for regulating circadian rhythms and supporting healthy sleep patterns.
“In the UK, for example, winter sunrises occur much later than in summer. Starting the day an hour earlier under permanent DST would further limit morning light exposure, compromising circadian regulation. This impact is particularly pronounced in northern regions of the UK, where shorter winter days are more extreme.
“In summer, early sunrises largely mitigate concerns about reduced morning light, however, increased evening light under DST may delay sleep onset by suppressing melatonin and increasing alertness.”
What does the public say?
“Public opinion on DST is also increasingly polarised. Critics argue that in an era dominated by artificial lighting, within homes, workplaces, and commercial environments, the significance of natural daylight has diminished. A YouGov poll published in October last year, revealed that 46% of Britons support the continuation of DST, while 42% favour its abolition.”
Find out more about Dr Kelu’s research: https://www.kcl.ac.uk/people/jeffrey-kelu