The curse of time travel in spring and autumn

Podcast Transcript

Hello and Welcome to News From The Future, spoken by the eleven labs audio clone of Dr Catherine Ball.

In this new short series we will be focussing on Sleep. We all do it, and we all recognise when we have not had enough of it.

Dr Cath’s new book The Future of Sleep is out now and available in paperback from Amazon as well as on Kindle, and hopefully on Audible. We think you’ll get something life changing from it.

Today we are talking about something a bit controversial - Daylight Savings Time

Enjoy!

The biannual ritual of changing our clocks has far more significant health implications than most people realize. While that extra hour of sleep in autumn might seem like a welcome gift, research reveals a complex web of health effects tied to these time shifts, from increased heart attacks to higher rates of depression and traffic accidents.

Daylight Saving Time (DST) was first implemented in the UK during World War One in 1916, primarily to conserve energy and maximize daylight during working hours. Today, this practice affects roughly 70 countries and more than a quarter of the global population. In the United States, which formally adopted DST in 1966, clocks change on the second Sunday in March and first Sunday in November, while in the UK, the changes occur on the last Sunday in March and October.

The most concerning health impacts occur during the spring transition when clocks move forward. A 2014 U.S. study found a startling 24% increase in heart attacks on the Monday following the spring time change. This finding isn’t isolated – similar patterns have emerged in studies across Sweden, Croatia, Germany, Brazil, Finland, and Mexico. A comprehensive meta-analysis showed an average 4% increase in heart attacks following the spring transition, highlighting the widespread nature of this health risk.

The negative effects don’t stop there. Research has documented increased stroke rates in the weeks following the spring change. Mental health is also affected, with a 2020 study showing exacerbation of mood disorders, depression, anxiety, and substance abuse. Road safety becomes a serious concern too, with U.S. studies showing a 6% increase in fatal traffic accidents in the weeks after springing forward, attributed to the nation struggling with the loss of one hour of sleep.

The underlying mechanism for these health impacts relates to our circadian rhythms – our body’s internal 24-hour clock. Professor David Ray from the University of Oxford explains that sunlight is the primary signal our brain uses to synchronize this internal clock. The pineal gland produces melatonin at night when light levels fall, making us sleepy, while morning light triggers cortisol release for wakefulness. This delicate balance is disrupted when we artificially shift our schedules.

Spring’s clock change disrupts this system in multiple ways. Evening light interferes with melatonin production, making it harder to fall asleep, while darker mornings mean people wake up before their bodies are naturally ready. A 2024 study of over 11,000 UK residents found that while people lost about 65 minutes of sleep on the spring transition Sunday, there was evidence of catch-up sleep in subsequent days, suggesting some ability to adapt to the change.

The impact of disrupted circadian rhythms isn’t limited to clock changes. Shift workers provide a stark example of the long-term effects of living against our natural rhythms. Research shows they experience higher rates of mental and physical illness, including increased rates of diabetes, obesity, coronary heart disease, and cancer. They also have shorter life expectancies on average. Even people living on the western edge of time zones show similar health risks due to the constant slight misalignment with natural light cycles.

The autumn transition, while generally considered less problematic, isn’t without its effects. People typically only gain about 33 minutes of extra sleep, not the full hour, and continue to lose sleep throughout the following week. Danish research spanning 1995 to 2012 found an 11% increase in major depressive episodes in the 10 weeks following the fall time change, suggesting seasonal mood impacts.

However, there are some positive aspects to the autumn transition. Professor Joan Costa-i-Font from the London School of Economics tracked 30,000 individuals over 30 years and found some health benefits associated with the fall change, including increased energy levels and improved mood. People reported feeling better and happier with the additional sleep opportunity. Nevertheless, these benefits weren’t sufficient to offset the negative impacts of the spring transition.

The economic impact is substantial – Costa-i-Font’s research suggests that changing clocks twice yearly costs economies over €750 per capita annually. The disruption goes beyond immediate health effects, as the professor notes that while an hour might seem insignificant, the synchronized shift of entire populations creates widespread disruption to daily routines and biological rhythms.

The European Parliament voted to abolish DST in 2019, though implementation remains pending. The challenge lies in agreeing on which time to maintain – while most countries prefer summer time, circadian biologists generally recommend winter time as better aligned with our natural rhythms. This scientific perspective suggests that maintaining standard time would better support public health and natural sleep-wake cycles.

These findings raise important questions about the continued practice of DST, especially given the documented health risks. As Professor Ray emphasizes, even small misalignments can have significant impacts when applied across entire populations: “With a small risk applied to 60 million people, you’ll be dialing up quite a lot of disease that is completely avoidable.” The evidence suggests that while we might enjoy extra evening light during DST, the biological costs of these clock changes may outweigh their perceived benefits.

In the immediate term, as we face the autumn time change, we can at least take comfort in knowing that darker evenings naturally support better sleep patterns. However, the broader discussion about permanently ending biannual clock changes continues, driven by mounting evidence of their adverse effects on public health and wellbeing.

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