Researchers from the University of Cambridge and Fudan University argue that seven hours is the ideal amount of sleep for people in their middle years and upwards, with too little or too much sleep resulting in poorer cognitive performance and mental health.
Sleep plays an important role in enabling cognitive functioning and maintaining good psychological health. Besides, waste products help keep the brain healthy. As we grow older, we often experience changes in our sleep patterns, including difficulty falling asleep and staying asleep, as well as reduced quantity and quality of sleep.
Scientists from the United Kingdom and China conducted research on data from around 500,000 adults aged 38-73 years old from the UK Biobank. Participants were asked about their sleeping habits, mental health and wellbeing, and took part in a series of cognitive tests. Nearly 40,000 people were interviewed via brain imaging and genetic information.
By using these results, the team found that impaired cognitive performance was correlated with insufficient and excessive sleep duration, such as processing speed, visual attention, memory, and problem-solving skills. Seven hours of sleep per night was the best amount of sleep for cognitive performance, but also for good mental health, with individuals experiencing more symptoms of anxiety and depression and worse overall wellbeing if they reported sleeping for longer or shorter periods.
One potential explanation for the connection between inadequate sleep and cognitive decline is the loss of slow-wave deep sleep. Disruption to this type of sleep has been shown to be a link to memory consolidation as well as the build-up of amyloid, a key protein which, when it misfolds, may cause havoc in the brain, which is particularly beneficial for the brain''s ability to rid itself of harmful chemicals.
The study also found a link between the amount of sleep and the structure of brain regions involved in cognitive processing and memory, with larger changes again resulting in greater sleep.
Having a consistent seven-hour sleep every night, without excessive duration variation, was critical to cognitive performance and well-being. Previous studies have also shown that interrupted sleep patterns are linked to increased inflammation, indicating a susceptibility to age-related illnesses in older individuals.
Although we cant say that too little or too much sleep causes cognitive problems, our study of individuals over a longer period of time seems to support this notion. Despite this, the reasons why older people have poorer sleep are somewhat complex, influenced by a combination of our genetic makeup and our brain structure.
These findings suggest that inadequate or excessive sleep duration may be a risk factor for cognitive decline in ageing. This is supported by previous studies that demonstrate a link between sleep duration and the risk of developing Alzheimers disease and dementia, where cognitive decline is a hallmark symptom.
One of the authors of the research, Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge, said: "Being a good night sleep is vital at all stages of life, but particularly as we age. Having the ability to maintain good mental health and wellbeing, and avoiding cognitive decline, specifically for patients with psychiatric disorders and dementia.
The research was funded by the China National Key R&D Program, the Shanghai Municipal Science and Technology Major Project, the Shanghai Center for Brain Science and Brain-Inspired Technology, the 111 Project, the National Natural Science Foundation of China, and the Shanghai Rising Star Program.