The clocks go back on Sunday, giving the nation an extra hour in bed, but research suggests the health effects may be more complex than a simple bonus sleep.
Extra Hour Myth
Although people theoretically gain an extra hour in bed, studies show they do not typically sleep for the whole bonus 60 minutes. A University of Bristol study published in 2024 analysed sleep data from almost 12,000 people over the spring and autumn clock changes.
It found that while people slept around an hour less when the clocks went forward, they did not gain a full hour when the clocks went back. Participants slept for just over half an hour more after the autumn change than on the surrounding Sundays.
The effect on sleep for the rest of the week varied by gender. Men tended to sleep more on weekdays after both clock changes, while women often slept less on weekdays after the changes. Experts said this could be because women experience higher levels of insomnia and sleep difficulties, which are exacerbated by the clock changes. The findings were published in the Journal of Sleep Research.
Circadian Rhythm Disruption
The time shift temporarily disrupts the human circadian rhythm – the internal 24-hour biological clock that coordinates physical, mental and behavioural processes. This can break the synchronisation between external environmental cues, such as natural light and darkness, and internal body systems.
Hormonal cues like melatonin release and cortisol spikes shift, leading to temporary daytime sleepiness, brain fog, and reduced focus. The effect on sleep patterns after the clocks change is sometimes called “social jet lag”.
Mood and Seasonal Affective Disorder
Seasonal affective disorder (SAD) is a type of depression that usually happens in the winter, with symptoms including low mood, lack of interest in usual activities, restlessness and difficulty concentrating. The NHS says SAD is thought to be linked to reduced levels of daylight in winter, although the exact causes are unknown.
Some people with SAD find the clocks going back accelerates their symptoms, as evening light exposure is suddenly reduced. However, a review by researchers at Australia’s Swinburne University of data from 157 studies in 36 countries found no clear or consistent link between seasonal clock changes and significant declines in mental health.
Heart Health and Accidents
Evidence on clock changes and cardiovascular events such as heart attacks has been mixed, but leans towards a modest, short-term increase in risk after springing forward and no significant effect or a very small drop in risk after losing an hour in autumn. Researchers who identified an increased risk of heart attacks after the clocks go forward usually point to circadian rhythm disruption and sleep disruption.
Studies have also suggested a short-term increased risk of road traffic accidents after the clocks spring forward. Data from the AA in 2023 showed an 11% rise in crashes during the fortnight after the clocks went back in October. It said darker evenings, wet weather and slippery streets may all play a role, and driving in sudden darkness can increase reaction times and cognitive fatigue.
Appetite may also shift, as the internal biological clock naturally increases hunger in the evening and lowers it in the morning. Fatigue from mild sleep disruption can cause cravings for carb-heavy or comfort foods.
