As the clocks go back this weekend, many look forward to an extra hour in bed. However, research suggests that the autumn clock change may not be as beneficial as it seems, with studies linking it to an increased risk of depressive episodes. Meanwhile, the spring clock change, which robs people of an hour of sleep, has been associated with a rise in heart attacks, strokes, and road traffic accidents.
Daylight saving time (DST) was introduced in the UK in 1916 during World War One to conserve energy and maximise daylight. Around 70 countries now observe DST, with the US adopting it in 1966. In the UK, clocks go forward on the last Sunday in March and back on the last Sunday in October.
Evidence of health impacts is strongest for the spring transition. A 2014 US study found a 24% increase in hospital admissions for heart attacks on the Monday after clocks go forward. A meta-analysis of multiple studies calculated an average 4% rise in heart attacks following the spring change. Strokes also increase in the weeks after the spring shift, and a 2020 study linked DST to worsened mood disorders, depression, anxiety, and substance abuse.
Road traffic collisions rise too. US data show fatal car accidents increase by 6% in the weeks after the spring clock change, attributed to sleep loss. The disruption stems from the effect on circadian rhythms, which rely on sunlight to regulate sleep. More evening light in spring interferes with melatonin production, making it harder to fall asleep, while darker mornings delay natural waking.
A 2024 UK study of over 11,000 people found that mean sleep duration was 65 minutes lower on the Sunday of the spring change compared to the previous Sunday, though some catch-up sleep occurred later. Experts note that internal circadian clocks naturally align with light-dark cycles, so the problem arises from arbitrarily shifting time.
