Spring fatigue is real to half the population but invisible in the data

Half the people in the study said they suffer from spring fatigue. The data said they don't.

That discrepancy sits at the heart of a new study published in the Journal of Sleep Research by chronobiologists Dr. Christine Blume of the University of Basel and Dr. Albrecht Vorster of the University of Bern's Inselspital. For years, Blume had fielded calls from journalists every spring asking about the science behind spring fatigue, and for years, she had given the same answer: no one had actually studied it. That bothered her enough to do something about it.

Tracking exhaustion across four seasons

The researchers designed a longitudinal online survey that contacted participants every six weeks for a full year, starting in April 2024. A total of 418 people completed the study. Each time they were surveyed, participants reported how exhausted they had felt over the preceding four weeks, how sleepy they were during the day, and the quality of their sleep. By repeating these measurements across all seasons, the researchers could detect any genuine seasonal pattern in fatigue.

If spring fatigue were a real biological phenomenon, the data should have shown it. The transition from winter to spring involves rapid changes in day length, and the conventional explanation for spring fatigue holds that the body needs time to adjust its circadian rhythms to the shifting light. If that were true, exhaustion should spike when day length changes most quickly.

It did not. The speed at which day length changed had no association with participants' reported exhaustion. Neither did the specific month or season.

A label in search of a syndrome

The researchers' interpretation is straightforward. Spring fatigue appears to be a culturally influenced phenomenon rather than a seasonal biological reality. Because the term exists and is widely accepted, people pay more attention to feelings of tiredness during spring and attribute them to a recognized condition. The label creates the observation, not the other way around.

There is a second layer to this. In spring, people often feel pressure to be more active, to take advantage of improving weather, to emerge from the slower rhythms of winter. When their actual energy level falls short of this expectation, the gap between how they feel and how they think they should feel becomes noticeable. Spring fatigue offers a socially accepted explanation for that gap.

Winter is the actual tired season

The study did find genuine seasonal variation in sleep and energy, just not in the direction that spring fatigue proponents would predict. Participants reported feeling more tired and sleeping slightly longer during the darker winter months, consistent with established chronobiological findings. The biological night, controlled by the body's internal clock, lasts somewhat longer in winter, which may account for increased sleepiness during that period.

The corollary should be that people feel more alert as days lengthen. And indeed, summer brought an interesting pattern: participants slept less, stayed up later, and were more socially active, yet did not report increased exhaustion. Shorter sleep in summer did not translate to greater tiredness, further undermining the idea that the spring transition causes a unique fatigue state.

What this study can and cannot claim

The study measured subjective reports of exhaustion and sleepiness, not objective biological markers like melatonin levels, cortisol rhythms, or actigraphy data. It is possible that subtle physiological changes occur during the spring transition that fall below the threshold of subjective detection or that are masked by other factors. A study with objective measures might capture something the surveys missed.

The sample, while sufficient for detecting seasonal trends, was drawn primarily from a German-speaking Swiss population. Spring fatigue as a cultural concept has different traction in different countries, and the phenomenon might manifest differently in populations where it receives less cultural reinforcement or where seasonal light changes are more dramatic.

Still, the mismatch between belief and evidence is the study's central finding. Blume notes that when media inquiries about spring fatigue arrive this year, she will be able to point to empirical data for the first time. Her practical advice for anyone feeling sluggish as winter fades: get as much daylight as possible, stay physically active, and make sure you are sleeping enough. Not because spring fatigue is real, but because those things help regardless of the calendar.