Dozens of studies and scientific research have been conducted over a long period of time and have concluded the importance of getting plenty of sleep.
A good night’s sleep helps our bodies adjust to themselves and function as they should, and this is linked to improved mental health and reduces the risk of many health conditions, including heart disease and diabetes.
Lack of adequate sleep has also been shown to be associated with conditions such as cognitive impairment and Alzheimer’s disease.
Surprisingly, however, too much sleep can damage our brains, according to the website of Science Alert.
Prolonged sleep can also be harmful
Researchers at the University of Washington School of Medicine have published a research paper that suggests that prolonged sleep may be associated with cognitive decline, as well as less sleep.
The research team wanted to find out how much sleep is linked to cognitive impairment over time. To do this, they looked at adults from the mid-70s to the late 100s on average, and followed them for four to five years.
During their study, 88 people showed no signs of dementia, while 12 showed signs of cognitive impairment (one with mild dementia and 11 with mild cognitive impairment before).
During the study, participants were asked to complete general cognitive and neurological tests to detect signs of cognitive decline or dementia.
Subsequently, the results of these tests were combined into a single score, called the Premature Alzheimer’s Cognitive Disease (PACC) score. The higher the score, the better their opinion over time.
For four to six nights, sleep was measured using a monopolar electroencephalogram (EEG) worn on participants’ foreheads during sleep.
This was done once three years after people first completed their annual cognitive tests. This electroencephalogram allowed researchers to accurately measure brain function, which would tell them whether a person was sleeping (for how long) and how restful that sleep was.
Although sleep was measured only once during the study period, it still gave the research team a good indication of the participants’ normal sleep habits.
When using an EEG to measure the activity of the brain, people may become somewhat disturbed to sleep on the first night as they become accustomed to the device, and sleep will return to normal the next night. That is, when sleep is monitored from the second night onwards, it is a good representation of a person’s normal sleep habits.
The researchers also looked at other factors that could affect cognitive decline, including age, genes, and whether a person has symptoms of beta-amyloid or Dow proteins, both of which are linked to dementia.
Overall, the researchers found that sleeping less than 4.5 hours and more than 6.5 hours – with poor sleep – was associated with cognitive decline over time.
Interestingly, the effect of sleep time on cognitive function was similar to age, which is the greatest risk factor for cognitive decline.
We know from previous research that insomnia is associated with cognitive decline. For example, a study shows that people who report sleep disorders, such as insomnia or excessive daytime sleepiness, are more likely to develop dementia than those who do not.
Other research shows that beta-amyloid is high in the brains of people with short sleep patterns – a condition commonly found in the brains of people with Alzheimer’s disease.
Researchers are not sure why poor sleep is linked to cognitive decline. One theory is that sleep helps our brain flush out harmful proteins that form during the day.
Some of these proteins – such as beta-amyloid and Dow – are thought to cause dementia. So interfering with sleep can interfere with our brain’s ability to get rid of it. Experimental evidence also supports this – showing that even a night’s sleep can temporarily increase beta-amyloid levels in the brain of healthy people.
But it is not clear why long sleep is associated with cognitive decline. Previous studies have found an association between increased sleep and cognitive performance, but most participants relied on self-reporting how long they slept at night – meaning the data were less accurate than using EEG to measure brain function.
Therefore, this new study adds weight to such findings. Surprisingly, the results of this study show that better sleep duration is much shorter than previous studies have indicated that it is complicated.
Studies show that sleeping more than 6.5 hours is associated with cognitive decline over time – less so when we consider that older people are advised to sleep 7 to 8 hours each night.
The reason is that the length of sleep is not necessary, but the quality of that sleep is important when it comes to the risk of dementia. For example, this study shows that “slow” insomnia – restored sleep – especially affects cognitive impairment. What we cannot say from this study is whether long-term sleep can predict cognitive decline independently.
Importantly, we cannot rule out that participants who slept more than 6.5 hours each night may not have had cognitive problems prior to brain changes indicating dementia that was not picked up on the tests.
Although researchers are interested in correcting the factors associated with dementia, there may be other conditions that precede those who sleep longer, which may have contributed to a cognitive decline that is not taken into account. These include, for example, poor health, socioeconomic status, or level of physical activity.
Taken together, these factors may explain why long sleep is associated with cognitive decline.
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