Seven hours is the ideal amount of sleep for people in their middle age and upwards, with too little or too much sleep associated with poorer cognitive performance and mental health.
Good psychological health is dependent on good sleep. It helps keep the brain healthy by removing waste products. Difficulty falling asleep and staying asleep, decreased quantity and quality of sleep, and other alterations to our sleep patterns as we get older are some of the things we see. It is thought that sleep problems may contribute to cognitive decline in older people.
Scientists from the UK and China looked at data from nearly 500,000 adults from the UK Biobank. Participants were asked about their sleeping patterns, mental health and wellbeing, and took a series of cognitive tests. The study participants had access to brain and genetic data.
The team found that both insufficient and excessive sleep duration were associated with impaired cognitive performance, such as processing speed, visual attention, memory and problem-solving skills. The optimal amount of sleep for cognitive performance was seven hours per night, but also for good mental health, with people experiencing more symptoms of depression and anxiety and worse overall wellbeing if they reported sleeping for longer or shorter durations.
The disruption of slow-wave sleep may be one reason for the association between insufficient sleep and cognitive decline. Disruption to this type of sleep has been shown to cause a build-up of amyloid in the brain, which can cause tangles in the brain. Lack of sleep may affect the brain's ability to rid itself of toxins.
The team found a link between the amount of sleep and differences in the structure of brain regions involved in cognitive processing and memory, with greater changes associated with less than seven hours of sleep.
It was important to have a consistent seven hours of sleep each night, without too much change in duration. Studies have shown that interrupted sleep patterns are associated with increased inflammation and susceptibility to age related diseases in older people.
The professor from Fudan University in China said that their analysis looked at individuals over a longer period of time and it appears that the idea of too little or too much sleep causes cognitive problems. The reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic makeup and the structure of our brains.
According to the researchers, insufficient or excessive sleep duration may be a risk factor for cognitive decline in old age. The link between sleep duration and the risk of developing Alzheimer's disease and dementia is supported by previous studies.
Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge is one of the study's authors. It is important to find ways to improve sleep for older people to help them maintain good mental health and wellbeing and avoid cognitive decline.
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 National Natural Sciences Foundation of China and the Shanghai Rising Star Program.
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