To understand what shift work does to the body, it’s worth looking at what emerging research suggests about sleep itself. Sleep does far more than give the brain and body a rest.
When we are asleep, our brain consolidates the memories of the day, processes emotions, and solves problems that defied it in the waking hours. It also strengthens immune defences and repairs muscle tissue.
Prof Russell Foster is a sleep scientist at Oxford University, who has spent a career studying the biology of the sleeping brain.
“Sleep is a pillar of our health,” he says, “in the same way we think about diet and exercise. We have to take control of it.”
In that light, the strain of shift work becomes easier to see: it’s not solely about being tired, but potentially about repeatedly disrupting a system that’s doing far more behind the scenes than many people realise.
One of the most remarkable discoveries of recent years is that while we sleep, the brain cleans itself. Deep within the grey matter is plumbing called the glymphatic system. Fluid runs along tiny channels beside the brain’s blood vessels, washing away the waste products that accumulate during waking hours.
So, what happens to these toxins when sleep is disrupted?
Prof Hugh Markus, a neurologist who leads the stroke medicine group at the University of Cambridge, has begun to answer this question.
Markus and a medical student, Yutong Chen, analysed the brain scans of more than 40,000 people drawn from a vast database of health records and medical scans built up over more than a decade at the UK Biobank. All of them were healthy when their scans were taken.
The researchers found they could identify those whose drainage systems were struggling. Critically though, they discovered that those with the most impaired drainage systems were significantly more likely to go on to develop dementia years later, according to Markus.
“Disruption of that flow,” he says, “was playing an important role in predicting who would get dementia, in large numbers of people in the normal population.”