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Why seven hours is the ideal amount of sleep for middle-aged and older people, say University of Cambridge researchers

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Scientists have declared seven hours to be the ideal amount of sleep for middle-aged and older people.

A study of nearly half a million adults suggests too little or too much sleep could be associated with poorer cognitive performance and mental health.

Some people find it harder to sleep as they grow older (56401257)
Some people find it harder to sleep as they grow older (56401257)

The researchers at the University of Cambridge and Fudan University, in China, say having a consistent seven hours’ sleep each night, without too much fluctuation in duration, was also found to be important to cognitive performance and good mental health and wellbeing.

Sleep is also known to keep the brain healthy by removing waste products.

But as we age, we often find our sleep patterns altering, with some people having difficulty falling asleep or staying asleep, meaning the quantity and quality of sleep may decline.

Such sleep disturbances could contribute to cognitive decline and psychiatric disorders in the ageing population.

Prof Barbara Sahakian, from the Department of Psychiatry at the University of Cambridge, one of the authors of the study published in Nature Aging, said: “Getting a good night’s sleep is important at all stages of life, but particularly as we age.

“Finding ways to improve sleep for older people could be crucial to helping them maintain good mental health and wellbeing and avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias.”

The researchers analysed data from nearly 500,000 adults aged 38 to 73 from the UK Biobank. They were asked about their sleeping patterns, mental health and wellbeing, and took part in a series of cognitive tests. There was also brain imaging and genetic data for almost 40,000 of the study participants.

Both insufficient and excessive sleep duration were found to be associated with impaired cognitive performance, such as processing speed, visual attention, memory and problem-solving skills.

Seven hours is the optimal amount of sleep as we reach middle and older age, Cambridge scientists have declared (56401259)
Seven hours is the optimal amount of sleep as we reach middle and older age, Cambridge scientists have declared (56401259)

The researchers concluded that seven hours of sleep per night was the optimal amount for cognitive performance, but also for good mental health. People who reported sleeping for longer or shorter durations reported more symptoms of anxiety and depression.

The scientists believe a possible reason for the association between insufficient sleep and cognitive decline is the disruption of slow-wave or ‘deep’ sleep.

This has been shown to impact memory consolidation and be associated with the build-up of amyloid. When this critical protein misfolds, it can cause ‘tangles’ in the brain characteristic of some forms of dementia.

A lack of sleep may hamper the brain’s ability to rid itself of toxins.

The study also found a link between the amount of sleep and differences in the structure of brain regions involved in cognitive processing and memory. Again, there were greater changes associated with those who typically had more or less than seven hours of sleep.

Prof Jianfeng Feng, from Fudan University in China, said: “While we can’t say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea. But the reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic make-up and the structure of our brains.”

The scientists conclude that Insufficient or excessive sleep duration may be a risk factor for cognitive decline in ageing.

This is supported by previous studies that have reported a link between sleep duration and the risk of developing Alzheimer’s disease and dementia, in which cognitive decline is a hallmark symptom. Previous studies have also shown that interrupted sleep patterns are associated with increased inflammation, suggesting increased susceptibility to age-related diseases in older people.

The research was supported by the National Key R&D Program of China, the Shanghai Municipal Science and Technology Major Project, the Shanghai Center for Brain Science and Brain-Inspired Technology, the 111 Project, the National Natural Sciences Foundation of China and the Shanghai Rising Star Program.

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