▎ WuXi AppTec content team editor
Hey, wake up, one more day of work to usher in a long vacation!
Just this night, how did you sleep, how long did you sleep?
We all know that only by sleeping well can we have health. Many studies have taught us that good sleep not only makes us feel refreshed, but also helps us improve our cognitive abilities, maintain mental health, and even remove toxins from our brains. But as they age, many people suffer from erratic sleep quality: it is often difficult to fall asleep, and sleep quality and duration are also affected.
Image credit: 123RF
Is it healthiest to sleep for a few hours? There have been many studies that illustrate the relationship between sleep time and different health indicators from different perspectives. For example, long-term sleep of less than 6 hours is not only associated with myocardial infarction, stroke, and an increased risk of atherosclerosis death, but also makes people more likely to develop Alzheimer's disease; at the same time, sleep deprivation also makes people more likely to gain weight and accumulate abdominal fat.
Now, in a study published in Nature Aging, a team led by Professor Feng Jianfeng of Fudan University has answered this question from another perspective: For middle-aged and elderly people, sleeping 7 hours a day is most beneficial to brain health, and sleep time is too short or too long, and cognitive ability, mental health and brain structure will have non-linear decline.
In the study, the research team obtained multiple data from the Uk's Biobank database on nearly 500,000 middle-aged and elderly people between the ages of 38 and 73, including their sleep patterns, mental health status, and their performance on a series of cognitive tests. In addition, the research team obtained brain imaging and genomic data for nearly 40,000 of them.
After analyzing the above data, the research team found that participants who slept for 7 hours were not only in the best state in the cognitive tests of information processing speed, attention, memory and problem-solving ability, but also had a better mental state: they had a lower proportion of anxiety and depressive symptoms. Conversely, the farther away from 7 hours of sleep, the worse the average state of cognition and mental health.
▲The relationship between sleep duration and cognitive performance and mental health (Source: Reference[1])
Combined with the brain imaging results, the team also found a relationship between sleep duration and brain structure: the volume of brain areas and cortical thickness of people who slept for 7 hours involved in cognition and memory function were also larger, specifically, including the central anterior gyrus, the lateral orbitofrontal cortex, the left insula and the hippocampus.
Why does sleeping too much or too little sleep, and the health of the brain seems to be poor? Taking cognitive performance as an example, the authors combine previous research and put forward some conjectures.
In the case of sleep deprivation, a decline in cognitive performance may be associated with slow-wave sleep disturbances. Slow-wave sleep has been found to be associated with memory consolidation and amyloid accumulation. Amyloid should be familiar to everyone: the tangle formed by the misfolding of this type of protein may induce neurodegenerative diseases. When sleep is low, the lymphoid system's process of using cerebrospinal fluid to flush metabolic waste products is also affected.
On the other hand, sleeping too long may reflect a stronger physiological need for sleep, or because of compensation for poor sleep quality, sleep fragmentation, so statistically, the cognitive performance of these people is also significantly reduced.
This study reveals the association of sleep duration with numerous indicators (Image source: Reference[1])
In addition to the average duration, it is also important to keep your sleep time stable. If they could maintain about 7 hours of sleep and avoid large fluctuations, the participants' cognitive performance and mental health were also better. Previous studies have also pointed out that irregular sleep patterns are also associated with increased inflammation, which further increases the risk of disease in the elderly.
In addition, the study also distinguished between different effects of sleep duration on participants of different ages. Whether it was the middle-aged group aged 39-52 or the older group, the conclusion that 7 hours was most beneficial to the brain was established. In fact, as we age, the effect of sleep duration on these indicators is waning, possibly because more older adults are affected by issues such as sleep fragmentation.
▲The relationship between sleep duration and cognitive and mental health in the elderly group is weak (Source: Reference[1])
Professor Feng said that although it is not yet possible to conclude that lack of sleep or excess can cause cognitive problems, the study provides supporting evidence for this view. However, the causes of poor sleep in the elderly are complex, and may be affected by a combination of genetic factors and brain area structure.
But at the very least, this study tells us that lack of sleep, or excess, may be a risk factor for cognitive decline.
Another author of the study, Professor Barbara Sahakian of the University of Cambridge, said: "Quality sleep is important at any stage of life, and this is especially critical as we get older. Finding ways to improve sleep quality for older adults is a key step to help them maintain their mental health and avoid cognitive aging. ”
Resources:
[2] Seven hours of sleep is optimal in middle and old age, say researchers. Retrieved Apr. 28, 2022 from https://www.eurekalert.org/news-releases/950961
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