The clock hands move forward and backward by one hour every six months. The effects and health impacts have been scientifically measured and confirm that these shifts disrupt the body’s balance, particularly sleep quality and increased daytime sleepiness, thus affecting alertness.
Everyone bears the brunt, but especially the evening chronotypes, the so-called “owls,” with somewhat milder repercussions in autumn compared to spring when the time change would be felt more acutely. The effects, though transient, should not be neglected. This emerges from a systematic, Italian review led by the Center for Sleep Medicine at the IRCCS Neuromed in Pozzilli, in collaboration with Pavia University, Mondino Foundation, National Research Council, University of Uninettuno and University of Genoa, published in Sleep Medicine Review.
The Study
The researchers conducted a comprehensive bibliographic search across multiple databases, following the PRISMA guidelines, selecting studies examining the impact of daylight saving time on sleep outcomes and daytime sleepiness in populations aged 6 to 85, using objective and subjective sleep measures. Among those reviewed, 27 studies from various countries were selected, revealing heterogeneous results: although the time change still exerts a negative effect on sleep, the worst effects would be observed in spring.
Indeed, the transition to daylight saving time appears to shorten sleep duration and degrade sleep quality, making it more disturbed and fragmented, leading to higher instances of daytime sleepiness. However, subjective differences emerge—specifically, chronotypes: those most exposed to the consequences of social clock shifts would be the “owls,” the evening chronotypes, people who tend to go to bed late and wake up late. By contrast, the return to standard time in autumn seems to have milder effects and, at times, even favorable ones, with a temporary increase in hours of sleep.
Implications
In general, the extended evening daylight associated with daylight saving time is more appreciated, yet later sunrises and sunsets disrupt the natural circadian rhythm, which is crucial for regulating the sleep–wake cycle.
Therefore, it is important to distinguish between the transient effects of switching to and from daylight saving time and the prolonged effects of staying on daylight saving time or standard time (ST) for extended health periods. The effects differ, tied to multiple factors: primarily, the abrupt biennial shift of the light-dark cycle and the reduction of opportunities for sleep in spring, and secondarily the chronic circadian misalignment during the daylight saving period.
This latter effect, in particular, can disrupt sleep rhythms, hormone production and other biological processes, especially if combined with short winter photoperiods, reducing morning light exposure needed to synchronize circadian rhythms.
Many studies to date have focused on evaluating the immediate effects of transitions from standard time to daylight saving time or from daylight saving time back to standard time, but in parallel evidence and studies are emerging on the long-term implications of chronic circadian misalignment detected through tools and technologies, not natural elements, which is, moreover, impossible. Indicators of misaligned clocks, such as time zone position, for example, suggest that alignment or misalignment between biological rhythms and social time due to daylight saving time yields significant, often negative, outcomes in health, safety, and productivity.
Health Outcomes and Impacts of Time Change
Sleep deprivation, experts explain, aligns more closely with our internal clock because the sun, closer to solar noon at its zenith, would promote a more natural sleep–wake rhythm. This is why the scientific community regards permanent sleep deprivation as opposed to permanent daylight saving time as a crucial motivation to end the seasonal clock changes: a time scheme more in line with human circadian biology would foster better sleep quality and overall health. According to the latest scientific evidence, sleep disorders, such as those potentially caused by daylight saving transitions, would correlate with an increased risk of cardiovascular disease, metabolic dysregulation, and cognitive deficits, in contrast to earlier studies that reported conflicting results, in some cases showing negligible effects on sleep and in others clear evidence of significant sleep disruption and increased daytime sleepiness after the daylight saving transition.
Strengths and Limitations
On one hand, the current systematic review clarifies several aspects of daylight saving time and time changes on sleep quality, duration, and daytime sleepiness in children and adults, with information that could steer broad public health and policy choices in shaping effective health and wellness strategies for individuals.
On the other hand, the available research, by methods and samples, shows heterogeneous results: in particular, the lack of polysomnography-based studies calls for further research, larger and standardized, capable of providing answers about long-term outcomes. It is true that small samples, differing methodologies, and non-comparable measurement tools prevent definitive conclusions.
Sources
Romigi A, Franco V, Scoditti E et al. The effects of daylight saving time and clock time transitions on sleep and sleepiness: a systematic review. Sleep Medicine Review, 2025, Vol. 84, 102161. Doi: https://doi.org/10.1016/j.smrv.2025.102161
Abbonati a Karla Miller
