Researchers from the University of Cambridge and Fudan University say 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.
Sleep plays an important role in enabling cognitive function and maintaining good psychological health. It also helps keep the brain healthy by removing waste products
In research published on April 28, 2022, in the scientific journal 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. By analyzing the 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.
Seven hours of sleep per night was the optimal amount of sleep for cognitive performance, but also for good mental health. People experienced more symptoms of anxiety and depression and worse overall well being if they reported sleeping for longer or shorter duration.
The researchers say 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 misfolds, can cause ‘tangles’ in the brain characteristic of some forms of dementia. Additionally, lack of sleep may hamper the brain’s ability to rid itself of toxins.
The 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.
Having a consistent seven hours’ sleep each night, without too much fluctuation in duration, was also important to cognitive performance and good mental health and well being. Previous studies have also shown that interrupted sleep patterns are associated with increased inflammation, indicating a susceptibility to age-related diseases in older people.
The researchers say the findings suggest that insufficient or excessive sleep duration may be a risk factor for cognitive decline in aging.
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.
Parvathy Sukumaran 
