Night shift work disrupts the human body’s internal clock, which evolved over millions of years to align with the sun’s cycle. This disruption affects millions of workers globally, including nurses, paramedics, engineers, lorry drivers, and factory workers, with significant health consequences that researchers are only beginning to fully understand.
Sleep serves critical functions beyond rest: the brain consolidates memories, processes emotions, and activates the glymphatic system, which clears waste products from brain tissue. Research led by neurologist Prof Hugh Markus at the University of Cambridge analyzed brain scans of more than 40,000 people and found that impaired drainage systems were significantly associated with later dementia development. A Swedish study tracking more than 13,000 shift workers for up to 41 years found that shift work in mid-life was associated with a 36% higher risk of dementia. Additionally, repeated sleep disruption can raise levels of amyloid and tau proteins, deposits linked to Alzheimer’s disease.
The health impacts extend beyond neurological concerns. An analysis of 35 studies found that sleep reduced to around 4.5 hours for three or more nights significantly raised immune system activity, leading to inflammation associated with heart disease. Disrupted sleep also raises cortisol, the stress hormone, which promotes insulin resistance and creates a self-reinforcing cycle of poor sleep. The World Health Organization’s International Agency for Research on Cancer has classified night shift work as “probably carcinogenic to humans,” citing evidence linking it to breast, prostate, colon, and colorectal cancers.
Researchers are now exploring whether biphasic sleep—two distinct sleep periods per day rather than one continuous block—might offer solutions. Dr Line Victoria Moen at Norway’s National Institute of Occupational Health is studying shift workers in the Arctic Circle, where midnight sun conditions force natural sleep disruption. Her research found that many workers naturally adopted biphasic sleep patterns, sleeping in two blocks rather than one exhausted stretch. This pattern mirrors pre-industrial sleep habits documented by historian Roger Ekirch, who found that biphasic sleep was predominant in Western society until artificial lighting changed nighttime economics in the mid-19th century.
Moen’s review of 11,000 scientific paper summaries found fragmented and poorly defined existing research on biphasic sleep. Several studies indicate that strategic napping during shift work—even 20 to 50 minutes—improves alertness and reduces drowsy driving. Moen’s full research results are expected later this year, with the goal of developing clinical guidelines to help shift workers understand that split sleep patterns may represent a natural biological rhythm rather than a sleep disorder, potentially improving both health outcomes and safety.
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