New research reveals the optimal sleep for middle age – and older.
Seven hours is the ideal amount of sleep for people in their middle age and upwards, say researchers from the University of Cambridge and Fudan University. And too little or too much is associated with poorer cognitive performance and mental health.
Longevity.Technology: Anyone who has struggled to concentrate or be at their best following a night of broken sleep will be aware that it plays a key role in enabling cognitive function and maintaining good psychological health; sleep also helps keep the brain healthy by removing waste products. As we get older, we often see alterations in our sleeping patterns, which can include having trouble falling asleep and finding it hard to stay asleep. There can also be a decline in the quantity and quality of sleep, and it is thought that these disturbances may contribute to cognitive decline and psychiatric disorders in the aging population.
In 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 quizzed on their sleeping patterns, mental health and wellbeing, as well as completing a battery of cognitive tests. The researchers also used brain imaging and genetic data that were available for almost 40,000 of the study participants [1].
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When the research team analysed the data, they discovered that both insufficient and excessive sleep duration were associated with impaired cognitive performance, affecting processing speed, visual attention, memory and problem-solving skills. They found that seven hours per night was the optimal amount not only for cognitive performance, but also for good mental health; their research showed that people experienced more symptoms of anxiety and depression, and worse overall wellbeing if they slept for longer or shorter durations.
According to the researchers, one possible reason for the association between insufficient sleep and cognitive decline could be the disruption of slow-wave sleep – what we’d think of as “deep sleep”. Disruption of this type has been shown to have a close link with memory consolidation as well being associated with a higher rate of β-amyloid accumulation – a key protein, the misfolding of which can cause degenerative plaques in the brains of dementia sufferers [3]. Additionally, it may hamper the brain’s ability to rid itself of toxins.
The team also discovered a link between the amount of sleep and differences in the structure of brain regions involved in cognitive processing and memory, finding greater changes associated with more or less than seven hours of sleep.
Getting seven hours’ a night, without too much fluctuation in duration, was also important to cognitive performance and good mental health and wellbeing – consistency is key. Previous studies have also shown that interrupted sleeping patterns are associated with increased inflammation, indicating a susceptibility to age-related diseases in older people.
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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 [2].”
This research suggest that insufficient or excessive sleep duration may be a risk factor for cognitive decline in aging, say the researchers. This is supported by previous studies detailing links between duration and the risk of developing Alzheimer’s disease and dementia, in which cognitive decline is an obvious symptom.
Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge, one of the study’s authors, 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 [2].”
[1] https://www.nature.com/articles/s43587-022-00210-2
[2] https://www.cam.ac.uk/research/news/seven-hours-of-sleep-is-optimal
[3] https://www.sciencedirect.com/science/article/pii/S0960982220311714
