Many of us are looking forward to an extra hour in bed on Sunday as the clocks go back. Winston Churchill once described Daylight Saving Time as: “An extra yawn one morning in springtime, an extra snooze one night in autumn.” But is it that simple?
Research has found the return to Greenwich Mean Time each autumn can have some surprising health effects. Here’s how the clocks going back might affect you this week.
The ‘bonus hour’ myth
Although we theoretically gain an extra hour in bed, research shows people do not typically sleep for the whole of that bonus 60 minutes. A University of Bristol study published 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.
And the effect on sleep for the rest of the week varied depending on gender. Men tended to sleep more on the weekdays after both clock changes, while women often slept for less on the weekdays after the clock changes than before.
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 shift in time temporarily disrupts the human circadian rhythm – the internal 24-hour biological clock that coordinates physical, mental and behavioural processes.
When the clocks shift, this can break the synchronisation between external environmental cues (exposure to 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 of circadian rhythm disruption on sleep patterns after the clocks change is sometimes called “social jet lag”.
Mood changes and seasonal affective disorder (SAD)
Seasonal affective disorder (SAD) is a type of depression that usually happens in the winter. Symptoms include low mood, a lack of interest in things you usually enjoy, restlessness and difficulty concentrating.
The NHS says SAD is thought to be linked to reduced levels of daylight in the winter, although the exact causes are unknown. Some people with SAD find that the clocks going back accelerates their symptoms. Although the mornings are lighter, evening light exposure is suddenly reduced.
People without SAD may also notice an effect on their mood as a result of evenings feeling darker. However, the evidence is mixed. A recent 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 about the effects of clock changes on cardiovascular events such as heart attacks has been mixed, but leans towards a modest, short-term increase in risk after they spring forward and no significant effect or a very small drop in risk after we lose an hour in autumn.
Researchers who have identified an increased risk of heart attacks in the days after the clocks go forward usually points to the effects of circadian rhythm disruption and sleep disruption.
Many cardiac experts agree that DST does not suddenly create new heart attack victims who were previously healthy, but may trigger events in people who were already at high risk.
Studies have also suggested there is a short-term increased risk of road traffic accidents after the clocks spring forward. And 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. Driving in sudden darkness after work can also increase reaction times and cognitive fatigue.
Appetite and metabolic shifts
Our internal biological clock naturally increases hunger in the evening and lowers it in the morning. You may notice your appetite increasing earlier in the day after the clocks go forward because your digestive and metabolic schedule is out of sync with the new time.
Fatigue from mild sleep disruption can also cause cravings for carb-heavy or comfort foods.
This story originally appeared on Express.co.uk
