Seven hours of sleep each night is the ideal amount for middle-aged and elderly people, research shows.
A study of nearly 500,000 adults between the ages of 38 and 73 found that both too much and too little sleep were linked to poorer cognitive performance and mental health, including anxiety and depression. Constant amount of sleep is also helpful.
Professor Barbara Sahakyan of the Department of Psychiatry at Cambridge University said: “For every hour you have been away from seven o’clock, you have gotten worse. It is very clear that the processes that take place in our brain during sleep are very important for maintaining our physical and mental health. “
Getting a good night’s sleep, she added, is important at all stages of life, but especially in old age. “I think it’s as important as how you exercise.”
A possible reason for the connection between insufficient sleep and cognitive decline may be a violation of slow-wave or deep sleep, which has been shown to be important for memory consolidation. Lack of deep sleep can also prevent the brain from clearing toxins effectively.
The study, which uses data from the UK’s Biobank, included brain imaging and genetic data from nearly 40,000 participants in the study. The brain area most affected by sleep has been found to be the area containing the hippocampus, the brain’s memory center, with too much or too little sleep associated with less brain volume. The analysis found that people who slept seven hours a night performed best on average in cognitive tests of processing speed, visual attention, memory and problem-solving skills.
However, the work could not prove a causal relationship, and the relationship between sleep and some brain disorders is complex. For example, unusual patterns of sleep and insomnia are common symptoms in people with dementia.
Scientists are less clear about why spending eight or more hours in bed can cause problems. One explanation is that people who have poor quality sleep disorders tend to sleep longer – or try to sleep – because they feel tired. “We really don’t understand why sleeping longer would be a problem,” Sahakyan said.
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Professor Jianfeng Feng from Fudan University in Shanghai said: “While we cannot say categorically that too little or too much sleep causes cognitive problems, our analysis of individuals over a long period of time seems to support this idea.
“The reasons why older people have worse sleep seem complex, influenced by the combination of our genetic makeup and the structure of our brains.
The study was published in the journal Nature Aging.
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