In a world that never truly sleeps, night shift has become a common work culture. From healthcare workers to security personnel, call center agents to factory employees, millions of people around the globe are wired into a schedule that goes against the grain of natural daylight. But what if your inability to adjust to late-night work wasn’t just about poor sleep hygiene or too much caffeine? What if the real culprit was buried deep inside your biology, an ancient evolutionary program that has kept humans in sync with the changing seasons long before clocks, lights, or even cities existed?

A study from the University of Michigan has begun to reveal this mystery. Led by researchers Daniel B. Forger and Ruby Kim, the study was published in npj Digital Medicine. It sheds light on a critical truth: the same internal mechanisms that helped our ancestors survive seasonal changes may now be hindering our ability to function in a 24/7 world. At the heart of this research lies one of the most misunderstood biological systems (our circadian rhythm) and its unexpected connection to seasonal adaptability.

The researchers closely tracked 3,000 medical interns already known for their grueling work hours and erratic sleep patterns. What emerged from the data was a remarkable insight. Those interns who displayed high variability in their behavior between seasons, such as a significant drop in step count or activity during winter as compared to summer, faced more difficulties in adjusting to shifting work schedules. On the other hand, interns whose daily movement patterns remained stable throughout the year adapted more easily to night shifts and irregular work hours. These individuals, it seems, had a better grasp on their internal clocks or rather, their clocks had a better grip on them.

This finding challenges our perception of modern humans as detached from nature. In the age of artificial lighting and climate-controlled environments, it’s easy to assume we’ve outgrown our seasonal dependencies. But this study reaffirms a critical biological truth that humans are seasonal beings. Whether we acknowledge it or not, our bodies respond to sunlight and darkness, to warmth and cold, to longer days and shorter nights. It’s a dance we’ve been performing since time began and it’s not easy to step out of rhythm.

One of the most striking revelations of the study is the concept that we do not operate with a singular internal clock. While most of us are familiar with the circadian rhythm which is a roughly 24-hour cycle that governs sleep, metabolism, body temperature, and hormone release, scientists now believe this system might be more intricate than previously thought. According to co-author Daniel Forger, we may actually have two internal timekeepers. One is aligned with dawn, the other with dusk. These twin clocks are in constant communication, helping us calibrate our daily functions to the shifting light of the day. When someone is exposed to unusual schedules, such as working through the night, these two clocks can fall out of sync, causing internal chaos that manifests as sleep problems, mood swings, cognitive fog, and even digestive issues.

What makes this study especially relevant for healthcare is the population it examines. Medical interns are often exposed to sudden, extreme changes in shift timings and workloads. Their health and performance (both critical to patient care) can suffer dramatically when their internal rhythms are disrupted. But beyond medicine, the findings carry implications for countless professions. Night shift workers are not just fighting fatigue they are fighting a biological resistance to shift their core rhythms. The inability to sync with irregular schedules isn’t about willpower or discipline. It’s about how each individual’s biology is wired to process change.

These revelations also bring attention to a silent health crisis. Long-term disruption of circadian rhythms has already been linked to serious health issues like obesity, diabetes, cardiovascular disease, and even certain cancers. But if seasonal adaptability is another key factor influencing how well we cope with night shifts, then personalized interventions may soon become the next step in occupational health. Perhaps in the future, wearable devices could help monitor individual circadian patterns and seasonal shifts in activity. Or employers could use behavioral data to tailor shift schedules to match each worker’s biological flexibility, minimizing health risks and optimizing productivity.

Another layer of complexity lies in how we define “health” in a workplace that demands constant availability. Modern society often praises hustle and 24-hour productivity, but studies like this remind us that ignoring our internal biology comes with consequences. Adapting to night shifts is not just about sleeping better during the day or eating at the right time. It may involve understanding your body’s reaction to the seasons, how your activity levels change with the weather, and whether your internal dawn-and-dusk clocks are in harmony or disarray.

In a culture that rewards round-the-clock effort, it’s worth reflecting on what we may be sacrificing. Sleep is not just rest, it’s recovery. Circadian rhythms influence how our organs function, how our brain processes information, and how our immune system defends against disease. Disrupting this rhythm has ripple effects that travel far beyond drowsiness. The findings from the University of Michigan reveal that some people, by nature of their seasonal biological patterns, are more vulnerable to these disruptions than others. The tragedy is that most of them are unaware until the effects begin to show in their health, productivity, and emotional well-being.

The study’s implications also extend to mental health, a concern that is increasingly intertwined with sleep and work patterns. Irregular shifts have been associated with depression, anxiety, and burnout. Understanding whether someone is seasonally sensitive could become an important part of early screening and prevention. If we can predict who is more likely to suffer from circadian misalignment based on how their activity varies across seasons, we could offer them strategies to reduce the strain before it becomes chronic.

These strategies may include light therapy, nutritional adjustments, scheduled naps, mindfulness routines, and, most importantly, flexible work structures. Employers may need to rethink their assumptions about shift rotations. It’s not enough to divide hours evenly or assume everyone adjusts the same way. A tailored approach to scheduling could not only reduce absenteeism and turnover but also create healthier, more sustainable workforces.

At a time when artificial intelligence and machine learning are being integrated into every corner of our lives, from smart watches to sleep trackers, we are in a unique position to align modern technology with ancient biology. Our bodies have always responded to nature’s cues. The sun rises, and our metabolism wakes up. The day ends, and melatonin prepares us for sleep. But when we dim the lights and demand productivity around the clock, we create a silent conflict within. The body resists. It warns us with fatigue, brain fog, illness, and in some cases, psychological distress.

The study led by Daniel Forger and Ruby Kim is a wake-up call. It reminds us that, despite our technological advancements, we remain creatures of the earth, deeply connected to its cycles. Our health depends on this connection, and ignoring it can come at a heavy cost.

In an ideal world, we would rise with the sun and rest with the moon. But in the real world, where emergencies don’t follow schedules and global economies demand round-the-clock attention, we must find a balance. This balance starts with awareness. Understanding how your body reacts to seasonal changes and irregular work hours can be the first step toward reclaiming control over your health. For those working night shifts, it might not always be possible to change your schedule, but knowing your body's limits and needs could help you decrease the damage.

Perhaps the most profound takeaway from this research is a reminder of something deeply human is that we are not machines. We are seasonal, cyclical, and deeply influenced by light and darkness, warmth and cold, rest and activity. The rhythm of the earth pulses within us still, no matter how modern our surroundings. And if we want to survive in a world that never sleeps, we must first learn how to listen to that ancient rhythm once again