When the clocks go back in October, millions of Britons welcome an extra hour in bed. But by the evening, with darkness arriving before many people finish work, that small luxury may seem a distant memory.
Author
- Laurence Wainwright
Departmental Lecturer and Course Director, Smith School of Enterprise and the Environment, University of Oxford
As autumn turns into winter, you might feel unusually tired, struggle to concentrate, or crave carbohydrate-rich comfort foods. Getting out of bed becomes harder, while a night on the sofa seems more appealing than going out.
It's tempting to dismiss this as the winter blues. But shorter days can influence our sleep and mood.
The clock change, which also happens in many other countries, doesn't reduce daylight. It shifts an hour of it from evening to morning. However, it coincides with shortening days, when some people struggle to get enough natural light.
For around 3% of the UK population , winter brings a form of depression known as seasonal affective disorder (SAD).
People with SAD experience recurring depressive episodes, usually beginning in autumn or winter and improving in spring. Symptoms include persistent low mood, irritability, difficulty concentrating and losing interest in enjoyable activities. It can also involve sleeping more, increased appetite and cravings for carbohydrates .
These symptoms can affect work and relationships. Other people experience milder seasonal changes without meeting the criteria for clinical depression, while some notice changes in sleep but little difference in mood.
What happens to our body clocks?
Our circadian system, or internal body clock, helps regulate when we feel alert and sleepy. Light-sensitive cells in the retina detect environmental light and signal to the brain's central clock. This helps coordinate daily rhythms, including the release of melatonin, a hormone involved in sleep.
Bright morning daylight helps synchronise that clock with the outside world. But someone who travels to work before sunrise, spends the day indoors, and returns after sunset may get relatively little natural light. Even on cloudy days, outdoor light is generally much brighter than typical office lighting.
Reduced daylight exposure can affect circadian timing and may contribute to seasonal changes in sleep and mood, although the mechanisms behind SAD aren't fully understood.
Research also suggests our sleep varies with the seasons. A 2025 study of sleep-tracking data from more than 116,000 adults found that people in the northern hemisphere slept approximately 15 to 20 minutes longer in winter than summer. These differences persisted despite artificial lighting and relatively fixed working hours.
Does turning the clocks back make matters worse? The evidence is mixed.
A Danish study reported more hospital contacts for depression following the autumn change. However, a 2025 study in England found fewer recorded depression-related health events in the following week. The studies measured different outcomes; neither proves that changing the clocks causes seasonal depression.
An ancient biological response?
Evolutionary biology offers one possible explanation for winter lethargy. For our ancestors in temperate climates, winter brought colder conditions and less predictable food supplies. Searching for food in harsh weather could be risky, so conserving energy might have offered a survival advantage.
Researchers have proposed that the increased sleep, appetite and weight gain associated with some cases of seasonal depression reflect an inherited tendency to conserve energy when food is scarce.
It's an intriguing hypothesis, but difficult to test. We cannot conclude that modern humans have an automatic, evolutionarily programmed slowdown in metabolism whenever daylight declines.
Seasonal depression is complex, with genetic susceptibility, circadian rhythms and environmental circumstances potentially contributing. Nevertheless, our sensitivity to seasonal light raises questions about modern working life. Most workplaces expect similar productivity throughout the year, even though opportunities to spend time outdoors can differ considerably between July and November.
Working with the seasons
There are practical steps that may help. The NHS recommends getting outside during daylight, exercising regularly and keeping consistent sleeping and waking times. Staying connected with other people can also help.
For SAD, treatment options include cognitive behavioural therapy and antidepressants. Research on particular medicines needs careful interpretation. A small study involving 37 patients suggested that agomelatine might improve symptoms, while a Cochrane review found that bupropion could help prevent recurrence in people with a history of winter depression. The latter evidence doesn't establish its effectiveness for treating an episode already underway.
Bright-light therapy may also help some people, although NICE says evidence of its effectiveness remains uncertain.
Anyone experiencing persistent depressive symptoms should speak to a GP rather than assuming they're simply tired because it's winter. Workplaces could help too, by making it easier for staff to spend time outdoors during daylight.
As the evenings draw in, recognising the biological influences on mood and energy may help us respond more effectively, without expecting another coffee to solve everything.
Laurence Wainwright does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
