Seven hours of sleep is the ideal amount of sleep for people in their middle age and upwards according to researchers from the University of Cambridge and Fudan University, who also associated too little or too much sleep with poorer cognitive performance and mental health.
In the research published in Nature Aging, scientists from the UK and China examined data from nearly 500,000 adults aged 38-73 years from the UK Biobank. Participants were asked about their sleeping patterns, mental health and well-being, and took part in a series of cognitive tests. Brain imaging and genetic data were available for almost 40,000 of the study participants.
The team analysed these data and found that both insufficient and excessive sleep duration was associated with impaired cognitive performance, such as processing speed, visual attention, memory and problem-solving skills. Seven hours of sleep per night was the optimal amount of sleep for cognitive performance, but also for good mental health, with people experiencing more symptoms of anxiety and depression and worse overall wellbeing if they reported sleeping for longer or shorter durations.
The team says one possible reason for the association between insufficient sleep and cognitive decline may be due to the disruption of slow-wave - deep sleep. Disruption to this type of sleep has been shown to have a close link with memory consolidation as well as the build-up of amyloid - a key protein which, when it misfiles, can cause ‘tangles’ in the brain characteristic of some forms of dementia.
The research team also found a link between the amount of sleep and differences in the structure of brain regions involved in cognitive processing and memory, again with greater changes associated with greater than or less than seven hours of sleep.
Professor 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 makeup and the structure of our brains.”
