The ideal amount of sleep has been shared for middle to older aged people, according to a study.
Too much and too little sleep are both associated with poorer cognitive performance and mental health, according to researchers from both Cambridge University and Fudan University in China. Scientists analysed data from nearly half a million adults aged 38-73, from the UK Biobank. Participants were all asked about their sleeping patterns, mental health and well-being as well as taking part in cognitive tests.
Genetic data and brain imaging was available for almost 400,000 of the participants, with the researchers' analysis indicating that seven hours of sleep was the optimal amount for peak cognitive performance, such as processing speed, visual attention, memory and problem-solving skills, reports Wales Online.
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It was also optimal for good mental health, with people experiencing more symptoms of anxiety and depression, and worse overall well-being, if they reported sleeping for longer or shorter amounts. 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.
Professor Jianfeng Feng, from Fudan University, 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. 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 researchers say the findings suggest 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.
Professor Barbara Sahakian, from Cambridge University’s Department of Psychiatry, 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 research is published in the journal Nature Aging.
