Why Night shifts hit you harder than others—the hidden reason revealed

The world doesn’t sleep, and neither do millions of night shift workers who keep hospitals running, deliveries moving, and cities alive after dark. But while the economy may thrive 24/7, the human body wasn’t exactly designed to follow suit. For many, working through the night means battling brain fog, sleep disruption, and a constant sense of jet lag. Why do some people seem to handle these irregular hours better than others? A fascinating new study suggests the answer might lie not in how tired we are, but in how seasonal we are.

A groundbreaking study suggests that your ability to adjust to late-night work might be rooted deep within your evolutionary biology. A research which was recently published uncovers a fascinating link between our seasonal adaptability and how we cope with irregular work schedules, especially night shifts.

Seasonal Bodies in a Non-Seasonal World

Despite living in a modern environment filled with artificial lighting and climate control, our bodies are still wired for the rhythms of nature. According to lead authors Daniel B. Forger and Ruby Kim, the same internal systems that help us adapt to the changing seasons also influence how well we handle disruptions to our sleep-wake cycles.

“We're more seasonal than we care to admit,” said Ruby Kim. “Daylight length, especially, plays a strong role in regulating our internal physiology. That seasonal timing can affect how flexible—or inflexible—we are when our daily schedules get flipped.”

The Study: Interns, Step Counts, and Sleep Disruptions

Researchers tracked over 3,000 medical interns across various hospitals, analyzing their activity data, sleep patterns, and work schedules. What they found was striking: individuals whose physical activity varied significantly between seasons—say, being more active in summer and less so in winter—were less able to cope with night shifts and abrupt changes in sleep schedules.

In contrast, those whose step counts remained consistent year-round, indicating less seasonal variation in behavior, showed greater resilience to working nights or rotating shifts.

Two Internal Clocks, One Sleep Puzzle

Co-author Daniel Forger explained that our internal clock isn’t a single mechanism but a dual system. “There’s not really one clock, but two,” he said. “One is trying to track dawn, the other tracks dusk, and they constantly communicate with each other. The way they sync or conflict can determine how we respond to schedule changes.”

This insight marks a significant shift in understanding circadian rhythms. While it's well known that the circadian rhythm controls sleep, digestion, and hormone release based on day and night cycles, this is the first study to connect seasonal variation with adaptability to shift work.

What This Means for Shift Workers

The findings could have major implications for professions with irregular hours, such as healthcare, law enforcement, transport, and customer service. Understanding an individual’s biological response to seasonal cues might one day allow employers to tailor work schedules or offer personalized strategies for better shift adaptation.

Listen to Your Inner Seasons

This new research is a reminder that no matter how far we evolve technologically, our bodies are still deeply connected to nature’s rhythms. By acknowledging our seasonal biology and complex internal clocks, we might better understand not just sleep, but how to live and work in ways that align with our natural rhythms—making night shifts less of a nightmare.