The hidden cost of the night shift and how to sleep it off

By Pallab Ghosh Science Correspondent It is four in the morning, and the ward is quiet. A junior doctor has been on her feet for nine hours. She is tired, her muscles are sore and her eyes are straining, but when her shift ends at six in the morning and she finally gets home, she struggles to sleep. Her internal clock, built over millions of years of evolution to tune human biology to the rising and setting of the Sun, is insisting it is morning. Time to wake up. Time to be alert. No amount of darkness, earplugs or blackout blinds can entirely silence it. This is not a personal failing. It is a collision between the demands of her job and some of the deepest machinery in the human body. This is playing out, invisibly, in the lives of millions of shift workers. Among them are the nurses, paramedics, engineers, lorry drivers and factory workers, who keep the country running while everyone else sleeps. Image source, Getty Images Image caption, Scientists are beginning to explore the role sleep can play in mitigating the toll of night shifts And the scientific evidence about what this relentless battle with our own internal clocks and modern living costs them - in heart attacks, strokes, cancer, mental illness, and quite possibly their precious memories - is increasingly difficult to ignore. Now scientists are beginning to explore whether changing how we sleep can play a role in mitigating the toll of night shifts, and potentially alleviate the ill-effects of disrupted nights. Their studies are also testing a surprising theory: that splitting sleep into two separate blocks - rather than attempting to force one long stretch during the day - may in fact be the most effective sleep pattern for people working through the night. The cost of shift work 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? P