How Daylight Saving Time affects our health

On the last Sunday of October, Daylight Saving Time ends and clocks ‘fall back’ by one hour at 2am, returning us to Greenwich Mean Time (GMT). Dr Aiste Steponenaite, Sleep and Circadian Neuroscientist and Co-director of the University-based Sleep and Wellbeing Clinic, explains what DST is, the controversy around it and the steps that can be taken to minimise the health affects of this time shift.

What is Daylight Saving Time (DST)? When was it first introduced and why?

Daylight Saving Time (DST) is the practice of setting clocks forward by one hour in spring and back by one hour in autumn to extend evening daylight during the summer months. In the UK, DST begins on the last Sunday of March when clocks are set forward by one hour at 1 am and ends on the last Sunday in October when the clocks are set back one hour.

Why was it first introduced?

The idea of advancing clocks in summer was first proposed in 1907 by British builder William Willett who noticed that people kept their shutters closed in the early morning despite the sun being up and that evenings were dark relatively early. He believed a time shift would encourage people to wake up earlier and make better use of natural daylight.

Germany was the first country to adopt DST in 1916, during World War I, to conserve coal. The UK followed shortly after, implementing DST under the Defence of the Realm Act. Today, DST is observed in 71 countries and territories. The most common explanation for observing DST is to save energy, as people would use less electric light in the evenings. However, DST’s effectiveness and need remain debated.

Since its introduction, the UK has experimented with different DST formats, including British Double Summer Time (advancing clocks by two hours in summer), a period of permanent DST (GMT+1 year-round), and, since 1972, the current system of GMT in winter and GMT+1 in summer. The UK followed the EU standard for DST transitions established in 2002, which remains in place now.

Why is DST subject to criticism?

While DST is intended to provide more daylight in summer evenings and winter mornings, it has been widely debated due to its effects on health, the economy, and public wellbeing.

From a scientific and circadian perspective, DST can misalign our internal body clocks, especially when evenings remain bright for longer. This delay in natural light exposure can push back sleep start, potentially leading to sleep deprivation and affecting overall health. Our biological clocks are naturally set by the rising and setting sun, but DST forces us to follow an artificial clock, creating a mismatch that can have consequences for sleep and wellbeing.

If annual DST changes were abolished, there would be further discussion about whether to adopt permanent DST or remain on standard time year-round. Geographical factors also play a role—longitude and latitude influence sunrise and sunset times, meaning the effects of DST vary by location. Additionally, individual differences in circadian rhythms and lifestyles determine how significantly a person is affected by time shifts. Changes to social schedules and exposure to light due to DST transitions may impact health, productivity, and performance.

What evidence is there that DST affects our health?

Light is a crucial factor in regulating our health because it is the strongest synchronising signal for our internal circadian clock. This clock dictates when we feel alert, sleepy, hungry, and when we perform best mentally and physically. The best way to align our biological rhythms is by exposure to natural sunlight, especially in the morning, which helps reset our internal clock each day. Although we live according to social clocks, our body clocks are still influenced by the sun’s position.

There are some benefits to DST, such as increased daylight during free time after school or work, which can encourage outdoor activity. However, DST also has drawbacks, which can be short-term (acute) or long-term (chronic).

My recent systematic review examined the health impacts of DST transitions. We found that the spring clock change, when the clock is advanced by one hour, is associated with an increased risk of heart attacks (acute myocardial infarction) and fatal traffic accidents. However, we also found some positive effects, such as a reduction in crimes involving physical harm. The impact of DST on sleep duration was mainly observed in individuals with early work or school start times. No clear evidence was found for psychiatric effects or long-term circadian disruption. While DST has both positive and negative effects, mitigating risks—such as protecting those at higher risk of heart disease, addressing potential sleep loss for some, and implementing safety measures to reduce traffic accidents—should be prioritised.

What advice would you give to people looking to minimise the health effects of the time shift?

Not everyone is equally affected by DST transitions, but there are steps people can take to reduce any negative impact individuals may have:

1. Prioritise exposure to morning light – natural light in the morning is essential for resetting our body clock. Try to spend time outdoors soon after waking up. Since it will become lighter earlier in the morning after the time shift (by the clock), this light exposure helps your body clock recognize the earlier time and maintains your usual wake-up time relative to the clock, preventing a shift to later waking.
2. Gradually adjust your sleep schedule – in the days leading up to the clock change, if possible, shift your bedtime and wake-up time later by 15–30 minutes each day. Since you will gain an hour on the weekend, this pre-adjustment helps you ease into the later time relative to your body clock, which can help minimise the feeling of having to go to bed and wake up “too early” after the transition.
3. Maintain a consistent sleep routine – keeping regular sleep and wake times throughout the week (including weekends) can help stabilise your circadian rhythm and reduce the effects of time shifts. Resist the urge to oversleep significantly on the day of the change, as this can confuse your body clock further.
4. Be mindful of evening light exposure – ​continue to avoid bright screens and artificial lighting close to your bedtime. This helps you fall asleep faster and supports your body’s move to the adjusted schedule.
5. Maintain good sleep hygiene – this includes keeping a dark, quiet, and cool sleep environment, limiting caffeine intake in the afternoon and evening, and managing stress before bed. This consistent routine will help your body adapt smoothly to the new clock time.

Although most of these tips are beneficial all year round, making a conscious effort to give our bodies time to adjust and adapting our habits to the shifted clock times can help ease the transition and minimise its impact on our wellbeing.