Thousands of Brain Scans Reveal A Worrying Consequence of Night Shifts

Night shift work is not for the weak.

Staying awake from dusk through to dawn, as many nurses, doctors, and emergency responders do, seems to take a toll on the body and mind.

But does it have an impact on the brain?

Neuroscientists in Singapore have now found evidence that shift work is tied to brain volume losses in key parts of the brain.

If shift work is stopped, however, those reductions are partially recovered within two and a half years, on average.

What those losses and gains actually mean for human health or behavior is unclear.

A secondary analysis revealed a negative correlation between volume loss and cognitive performance: Increasing volume loss was associated with poorer performance on some, but not all, cognitive tests.

But the effect size is "very small", the authors warn, so the results "should be interpreted cautiously."

That said, there's an important clue in the details. The brain regions that showed significant volume losses also help govern our sleep cycles.

What's more, they are involved in many of the symptoms of shift work, like poorer emotional regulation and memory performance.

Shift workers tend to work long hours. (Thomas Northcut/DigitalVision/Getty Images)

The study is the largest of its kind and finds a change in brain volume where most previous analyses of shift work have not.

It analyzed MRI and long-term health data from 14,198 middle- to older-age adults with no medical issues who took part in the UK BioBank.

Among 2,122 shift workers, the researchers noticed a symmetrical pattern of modest volume loss in the right thalamus, which is part of the brain's information relay 'hub' and is closely involved in memory retrieval.

They also noticed modest volume loss in the left amygdala, which regulates emotional responses.

Brain scans revealed small yet detectable volume loss and white matter degradation among shift workers. (Welton et al., NeuroImage, 2026)

This was after accounting for age, sex, chronotype, and skull volume, among other factors, in their analysis.

"The selective thalamic and amygdalar volume loss observed in healthy shift workers may represent an early, subclinical marker of neural vulnerability linked to chronic circadian disruption," the team concludes, led by neuroscientist Thomas Welton.

"These regions are central to sleep-wake regulation, emotion, and attention, functions that are commonly affected in shift work-related fatigue and mood disturbance."

Challenges with regulating emotions are often tied to poor sleep, and shift workers are known to face higher risks of both sleep disorders and mental health problems.

Researchers have long speculated that a disrupted circadian rhythm is to blame.

Other factors that may contribute include a lack of sunlight or changes to eating times.

But just because some parts of the brain are shrinking does not mean they are necessarily dying. The brain is a flexible organ that can rewire itself to meet the challenges of the time.

Perhaps that is what it is doing for shift workers; maybe their brains are somehow compensating in a way that allows them to work through the night.

"It is possible," the authors note, "that individuals who fail to acquire these brain changes are unable to tolerate shift work and are therefore biased toward non-shift working roles."

The study took place only among older adults, which means it's not clear how the brains of younger workers may cope with the demands of shift work.

Further studies are needed to fully understand how different people respond and are affected.

Today, full-time shift workers make up about 10 to 17 percent of the US population, but by some estimates, roughly a quarter of the adult workforce currently labors during non-traditional hours.

Related: Sleepless Nights Could Drive Half a Million Cases of Dementia in The US Each Year

If this work repeatedly disrupts the body's natural circadian rhythm, it could have a long-term and measurable impact on the brain, but we won't know until those changes are studied further.

"In the "era of longevity", it is critical to understand the relationship between shift work and structure of the middle-older aged brain," Welton and colleagues write.

"The apparent reversibility of these [observed] structural effects within two years of ceasing shift work highlights a potential therapeutic window for prevention and recovery," they add.

The study is published in NeuroImage.