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The optimum amount of sleep is not too little but not too much – at least in middle and old age.
New research has found that around seven hours of sleep is the ideal night’s rest, with insufficient and excessive sleep associated with a reduced ability to pay attention, remember and learn new things, solve problems and make decisions.
Seven hours of slumber was also found to be linked with better mental health, with people experiencing more symptoms of anxiety and depression and worse overall well-being if they reported sleeping for longer or shorter stints.
“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,”Jianfeng Feng, a professor at China’s Fudan University and an author of the study published in the scientific journal Nature Aging, said in a statement.
“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.”
Researchers from China and the United Kingdom analyzed data from almost 500,000 adults ages 38 to 73 who were part of the UK Biobank – a long-term, government-backed health study. Participants were asked about their sleep 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.
Other research has found that older adults who have significant difficulty falling asleep and who experience frequent night awakenings are at high risk for developing dementia or dying early from any cause, while sleeping fewer than six hours a night has been linked to cardiovascular disease.
One reason for the link between too little sleep and cognitive decline could be because of disruption of deep sleep, which is when the brain repairs the body from the day’s wear and tear and consolidates memories. Too little sleep is also associated with the buildup of amyloid, a key protein that can cause tangles in the brain that characterize some form of dementia. The study also said it’s possible a prolonged sleep duration stems from poor quality, fragmented sleep.
Dr. Raj Dasgupta, spokesperson for the American Academy of Sleep Medicine and assistant professor of clinical medicine at the Keck School of Medicine at the University of Southern California, said that longer sleep durations had been associated with cognitive problems but it wasn’t entirely clear why.
“This sets a mark for future research and the search for treatment,” said Dasgupta, who wasn’t involved in the research. “Sleep is essential as we get older, and we need just as much as younger people, but it’s harder to come by.”