How much sleep do you really need? © Joe Waldron

Michael Mosley: How much sleep do you really need?

Bad news for people who love to boast about only needing four hours a night.

Recently, I celebrated my 62nd birthday. On the whole I am in pretty good shape, but one of the most annoying things about ageing is that over the years my sleep has become shallower and more fitful. These days I rarely get more than seven hours sleep a night, and I often get less. So how much does that really matter?

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A while ago I was involved in an experiment for the BBC series, Trust Me, I’m A Doctor, where we decided to assess the effects of sleeping fewer than seven hours a night. We asked a group of volunteers to come to the University of Surrey Sleep Research Centre.

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The volunteers were randomly allocated to two groups. One group was asked to sleep for six and a half hours a night, the others got seven and a half hours. After a week, the researchers took some blood samples and the volunteers switched sleep patterns. The group that had been sleeping six and half hours got an extra hour, and the other group cut an hour.

Throughout the study we asked our volunteers to complete computer tests, which showed, not surprisingly, that most of them struggled with mental agility tasks when they’d had less sleep. But the most interesting results came from the blood tests.

Dr Simon Archer, who helped run the study, was particularly intrigued by how changes in the amount of sleep affected their genes. “We found that overall there were around 500 genes that were affected – some that were going up, and some that were going down,” he told me.

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When the volunteers had reduced sleep, genes associated with inflammation, immune response and response to stress became more active. The team also saw increases in the activity of genes associated with diabetes and risk of cancer. The reverse happened when the volunteers added on an hour of sleep.

So even an hour’s extra sleep a night can make a significant difference. And when it comes to the impact of sleep it’s not just about quantity, but quality. A recent study carried out by researchers at the University of Rochester Medical School and published in the journal Science Advances showed how much deep sleep you get impacts the glymphatic system, a network of plumbing in the brain that piggybacks on blood vessels and pumps cerebral spinal fluid through brain tissue to wash away waste and toxic proteins like beta amyloid and tau.

Sleep often becomes lighter and more disrupted as we age, so this study reinforces and explains the links between ageing, sleep deprivation, and heightened risks of developing Alzheimer’s. So the clear message is that most adults need seven hours of quality sleep a night. The real challenge is, how do you get it?


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