How much sleep is enough, and how much is too much?
Not an easy question, because the need for sleep varies from person to person.
Age also plays a role.
Most of us know from experience that the next day at work will be rough after a late night out.
But it may be surprising to hear that sleeping more isn’t necessarily better, at least for those in their middle age or older, according to a new study published in the Nature Aging journal.
Researchers from the University of Cambridge in the United Kingdom and Fuhan University in China found that seven hours of sleep at night is ideal for middle-age or older people.
They also found that significantly less, but also more, sleep may lead to impaired mental health and poorer mental performance.
The researchers looked at data from almost 500,000 adults aged between 38 and 73, collected in the extensive UK Biobank database.
The subjects were asked about their sleep patterns, mental health and well-being, and also took part in a series of cognitive tests.
The researchers had access to MRI (magnetic resonance imaging) images of the brain and genetic data from almost 40,000 participants.
Overall, the researchers found that a consistent seven hours of sleep appear to be ideal for cognitive performance, general well-being and mental health in middle-aged and older people.
However, both too much and too little sleep resulted in the subjects being slower in tests, having a lower attention span and poorer problem-solving skills.
Their mental health also suffered, with an increase of anxiety and depression symptoms, and lower overall well-being.
The researchers suggest that a disturbance in slow-wave sleep – part of deep sleep – may be a possible reason for the cognitive performance decline.
Such a disturbance is associated with an accumulation of beta-amyloid molecules.
These protein deposits, found in large clumps in the brains of Alzheimer’s patients, are suspected of contributing to neuronal cell death.
Analysis of the brain scans also revealed a link between different sleep durations and differences in the structure of brain regions involved in cognitive processing and memory.
Among them was the hippocampus, which is considered the memory centre of the brain.
While the study does not describe causality, the findings suggest that insufficient or excessive sleep may be a risk factor for cognitive decline in old age, according to the researchers.
“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,” Fudan’s Professor Dr Feng Jianfeng said in a press release.
“But 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.”
Co-author Prof Dr Barbara Sahakian from Cambridge added: “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 well-being, and avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias.” – By Alice Lanzke/dpa