Sleep duration, mental problems, and dementia are all linked in older persons. However, the underlying genetic mechanisms and structural changes in the brain are unknown. It is thought that these sleep disturbances may contribute to cognitive decline and psychiatric disorders in the aging population.
A new study by scientists from the University of Cambridge and Fudan University identified a nonlinear association between sleep and genetic and cognitive factors, brain structure, and mental health as crucial measures. Scientists examined data from nearly 500,000 adults aged 38-73 years from the UK Biobank.
All the participants were asked about their sleeping patterns, mental health, and well-being and took part in cognitive tests. Brain imaging and genetic data were available for almost 40,000 study participants.
The analysis revealed that insufficient and excessive sleep duration was associated with impaired cognitive performance. It also revealed that seven hours of sleep is optimal for people in their middle age and upward.
Seven hours of sleep was also good for good mental health, with people experiencing more symptoms of anxiety and depression. Sleeping for longer or shorter durations was found to have worse impacts on overall wellbeing.
Scientists noted, “One possible reason for the association between insufficient sleep and cognitive decline may be the disruption of slow-wave – ‘deep’ – sleep. Disruption to this type of sleep has been shown to have a close link with memory consolidation and the build-up of amyloid – a key protein which, when it misfolds, can cause ‘tangles’ in the brain characteristic some forms of dementia. Additionally, lack of sleep may hamper the brain’s ability to rid itself of toxins.”
The scientists also discovered a relationship between sleep duration and differences in the structure of brain regions involved in cognitive processing and memory, with bigger changes linked with sleeping longer or sleeping less.
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 supports this idea. But the reasons why older people have a poorer sleep appear to be complex, influenced by a combination of our genetic makeup and the structure of our brains.”
Scientists noted, “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.”
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.”
- Li, Y, Sahakian, BJ, et al. The brain structure and genetic mechanisms underlying the nonlinear association between sleep duration, cognition, and mental health. Nature Aging; 28 Apr 2022l DOI: 10.1038/s43587-022-00210-2