Night shift work creates a biological conflict with the body’s internal clock, potentially increasing risks for dementia, heart disease, diabetes, and even cancer. New research suggests that adopting a “biphasic” sleep schedule—splitting rest into two blocks—may help mitigate these health tolls and potentially alleviating the ill-effects of disrupted nights.
The Biological Collision of Shift Work
For millions of night shift workers—including nurses, paramedics, engineers, lorry drivers, and factory workers—the demand to remain alert while the sun is down forces a persistent struggle against human evolution. This is not a personal failure, but a deep-seated collision between modern professional requirements and the body’s internal clock, which is biologically tuned to the rising and setting of the sun. Even in environments with blackout blinds, earplugs, or darkness, the body’s internal machinery insists it is time to be alert when the sun rises.
The health consequences of this battle are becoming increasingly difficult to ignore. Beyond the immediate exhaustion of long hours, researchers have linked shift work to a higher incidence of heart attacks, strokes, cancer, and mental illness. As Prof Russell Foster, a sleep scientist at Oxford University, explains, sleep is not merely a period of rest; it is a fundamental pillar of physiological health that consolidates memories, processes emotions, solves problems, strengthens immune defenses, and repairs muscle tissue.
“Sleep is a pillar of our health, in the same way we think about diet and exercise. We have to take control of it.” Prof Russell Foster, sleep scientist at Oxford University
Brain Health and the Glymphatic System
A critical discovery in recent years is the role of the brain’s “plumbing” system, known as the glymphatic system. During sleep, this network channels fluid along tiny channels beside the brain’s blood vessels to wash away waste products that accumulate during waking hours. Among these waste products are amyloid and tau proteins—the deposits that accumulate in the brains of people with Alzheimer’s disease. A single sleepless night measurably raises amyloid levels in the fluid surrounding the brain.
Prof Hugh Markus, a neurologist who leads the stroke medicine group at the University of Cambridge, investigated how sleep disruption impacts this cleaning process. Working with medical student Yutong Chen, Markus analyzed brain scans of more than 40,000 people from the UK Biobank, a database built over more than a decade. The researchers identified those whose drainage systems were struggling.
“Disruption of that flow was playing an important role in predicting who would get dementia, in large numbers of people in the normal population.” Prof Hugh Markus, neurologist at the University of Cambridge
The long-term risks are substantial. A study by researchers at the Karolinska Institute, which tracked over 13,000 shift workers for up to 41 years, found that shift work during mid-life was associated with a 36% higher risk of developing dementia, with the risk rising the longer someone had worked shifts. While experts caution that sleep disruption is not a direct cause, it acts as a potential risk factor for those already vulnerable.
“You wouldn’t say poor sleep causes dementia, but if you’re vulnerable, it’s a potential risk factor.” Prof Russell Foster, sleep scientist at Oxford University
Markus notes that while his data shows a possible link, there are other critical vascular factors at play, such as blood pressure, smoking, and diabetes, which also impact Alzheimer’s risk.
Biphasic Sleep as a Potential Mitigation Strategy
As scientists look for ways to protect night workers, the focus has shifted toward biphasic sleep. This strategy involves splitting total sleep time into two separate blocks rather than attempting to force one long stretch of rest during daylight hours. Scientists are testing the theory that this may be the most effective sleep pattern for people working through the night.
Current investigations are exploring how this approach influences melatonin levels, amyloid and tau protein clearance, and overall performance. Researchers suggest that the development of new clinical guidelines could be essential for the millions of workers who keep the country running.
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