This Sunday, March 29, marks the annual ritual of “springing forward,” where clocks advance by one hour. For many, it signifies the cheerful arrival of longer, brighter evenings, a welcome shift after the dark winter months. Yet this small temporal adjustment comes with a personal cost: a night of lost sleep and a body confused by the sudden change. While the practice of shifting time twice a year has become a familiar part of our calendars, it is far more than a mere bureaucratic tweak; it is a profound intervention into our biology, one whose effects ripple through our health and well-being in surprising ways.
The concept of seasonal time change was originally born from pragmatic concerns, notably energy conservation during the First World War, and was widely reintroduced in the 1970s. However, modern science reveals that this one-hour shift imposes a significant strain on our internal systems. At its core, the change disrupts our circadian rhythm—the intricate, genetically-influenced 24-hour clock that governs sleep, alertness, hormone release, and mood. While some individuals adjust within a few days, others may struggle for weeks or even months to recalibrate. This disruption is not merely about feeling momentarily tired; research links the spring change to measurable short-term increases in traffic accidents, heart attacks, and depressive episodes, highlighting that a seemingly minor change can have major consequences.
One of the most cherished aspects of the spring shift is the gift of extended evening daylight. Yet, from a physiological standpoint, this later light presents a paradox. Our bodies rely on environmental cues to prepare for sleep, and darkness triggers the release of melatonin, the hormone essential for sleep onset. When natural light persists late into the evening, it suppresses melatonin production, delaying our ability to fall asleep and potentially degrading sleep quality. Experts like circadian rhythm researcher Jeffrey Kelu note that this makes it harder for people to wind down naturally. Simple behavioural adjustments, such as using blackout curtains to mimic darkness, can help counteract this by giving the body the clear signal that daytime has ended.
The importance of maintaining a robust and aligned circadian rhythm extends far beyond nightly rest. When our internal clock is synchronized with the natural 24-hour day, it sends clear, timely signals for vital bodily functions. People with strong rhythms tend to maintain regular schedules effortlessly. Conversely, chronic disruptions—whether from irregular habits, jet lag, shift work, or nighttime light exposure—are associated with a higher risk of serious health conditions, including obesity, cardiovascular disease, type 2 diabetes, and hypertension. Recent studies even suggest a link between weakened circadian rhythms and dementia, underscoring that this internal timing system is foundational to our long-term health.
Given these impacts, there has been growing public and political momentum to abandon the twice-yearly clock changes altogether. In 2018, a European Union public consultation showed overwhelming support (84%) for ending the practice, though political agreement among member states ultimately stalled the proposal. If the changes were abolished, a critical question remains: which time should become permanent? The scientific consensus, as voiced by researchers like Kelu, strongly advocates for sticking with standard winter time, not permanent summer time. The reasoning is centered on the irreplaceable value of morning light exposure, which is crucial for resetting our internal clock each day and kickstarting our alertness and metabolism.
The argument against permanent summer time is compelling. Adopting it would mean that, for much of the year, many people would commute to work or school in total darkness, missing the vital morning sunlight. While artificial indoor light does influence our rhythms, its effect is weaker than that of natural daylight. Especially during the short days of winter, every moment of morning sun becomes precious. Depriving ourselves of that “tiny amount of light exposure,” as Kelu emphasizes, could exacerbate the health risks associated with circadian misalignment. Therefore, the path to healthier societies might not lie in chasing endless evening light, but in preserving our connection to the natural dawn, allowing our ancient internal clocks to run in harmony with the sun’s timeless cycle.
