Why the Clock change Disrupts Sleep: A Deep Dive into Your Body’s Internal Rhythms
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The annual shift back to standard time reveals just how deeply our daily lives are governed by the intricate interplay of sleep pressure and our internal biological clocks, often leading to a week of disrupted rest and altered moods.
The disruption of sleeping and waking patterns from the daylight saving clock change reveals a great deal about our everyday reliance on the interaction of sleep pressure and circadian clocks. Understanding the complex physiological changes occurring within us when the clocks “fall back” can shed light on why this seemingly minor adjustment has such a noticeable impact.
The Night the Clocks Turn Back: A Hormonal Shift
As Saturday evening approaches, and assuming minimal exposure to bright light, our bodies initiate a familiar process: the secretion of melatonin, a crucial hormone for regulating sleep timing. This hormone steadily accumulates in the bloodstream, peaking a few hours later before gradually declining until morning. However, melatonin doesn’t directly induce sleep; rather, it acts as a signal, a gentle reminder that sleep should be approaching.Even brief exposure to electric light can delay or even halt this sleep signal, depending on its intensity and color.
Simultaneously, as melatonin levels rise, the heat generated by our internal organs reaches its daily peak, followed by a drop – another key indicator that sleep is imminent. This explains why a warm bath before bed can often promote relaxation and sleepiness.
During the initial hours of sleep, the body’s core temperature continues to decrease, entering a phase of slow wave sleep. This is characterized by heightened neuronal activity and a slowing, more regular heart rate – the deepest and most restorative stage of sleep. The lowest core body temperature often coincides with the highest melatonin levels, dem
often feels more jarring than the spring shift, as it’s generally easier to move our clocks forward than backward.
the clock change often leads to a loss of sleep, particularly REM sleep, which is crucial for emotional regulation and typically occurs later in the sleep cycle. Our biological clock will still initiate the cortisol-driven waking process simultaneously occurring as the previous day, but we’ll be awake as cortisol peaks, potentially leading to a deflated mood.
Individual Variations in Response
The impact of the clock change isn’t uniform across the population. Approximately one in 100 people have delayed phase sleep syndrome, a genetic condition that makes it arduous to fall asleep before the early hours of the morning. These individuals may actually benefit from the clocks going back, at least temporarily, as their melatonin levels align more closely with the new schedule.
Similarly, 10-20% of late adolescents are biologically predisposed to sleep later. For them,the temporary shift may bring their sleep patterns closer to those of the rest of the household,though they may still experience morning sleepiness.
Conversely, about 1% of middle-aged individuals experience advanced-phase sleep syndrome, feeling the need to go to bed early and wake up very early. This group is disproportionately affected by the clock change, as it forces them to wait longer for sleep and wake up earlier than desired. Menopausal women experiencing hot flushes, whose body clocks tend to be advanced, also find the autumn clock change particularly challenging.
A Fleeting Disruption, a Lingering Question
While the disruption typically resolves within a week, the question remains: why do we subject our bodies to this annual strain? We willingly challenge the synchrony of our internal clocks for the sake of a few extra moments of daylight.
This article is republished from The Conversation under a Creative Commons license.Read the original article.
Citation: Why does putting back the clocks an hour disrupt us so much? (2025,October 25) retrieved 25 October 2025 from https://medicalxpress.com/news/2025-10-clocks-hour-disrupt.html. This document is subject to copyright.
