Although improving mental fitness and reducing many health risks, such as heart disease and diabetes, are linked to a good night's sleep;

As a very important thing to help the body repair itself and continue to function as it should.

After it was proven that not getting enough sleep is linked to "cognitive decline", and disease threats, including Alzheimer's disease.

Researchers at the University of Washington School of Medicine say that “this does not mean that we sleep more, more sleep is not always better,” based on a recent study published last September, and showed that “exactly, like getting a little sleep.” Sleeping for long periods of time may also be linked to cognitive decline.

Sleep duration has the same effect as age

The study was conducted on 100 elderly people, average ages between their mid-to-late 70s, who were followed for a period of 4 to 5 years, and an EEG device was placed over their foreheads over a period of 4 to 6 nights, to enable researchers to measure their brain activity. Accurately, and ascertain whether the person is asleep or not, how long he sleeps, the amount of rest he gets during sleep, and to know the amount of sleep that causes cognitive impairment over time.

The results were that 88 people showed no signs of dementia, while 12 people showed signs of cognitive impairment.

After the researchers took into account other factors that can influence cognitive decline, including age and genes.

They found that sleeping less than 4.5 hours and more than 6.5 hours a night is on par with poor sleep in terms of their association with cognitive decline over time.

Interestingly, the effect of sleep duration on cognitive function was similar to that of age, making sleep duration the biggest risk factor for cognitive decline.

The quality of our sleep can affect our health, socioeconomic status, or levels of physical activity (pixels)

One night of sleep deprivation can harm you

Studies have also found that "people who suffer from sleep disturbances, such as insomnia or excessive daytime sleepiness, are more likely to develop dementia, compared to those who do not."

Other research has also indicated that "people who get short sleep times - even for just one night - have higher levels of beta-amyloid protein, which is commonly found in the brains of people with Alzheimer's disease."

Although the researchers don't know exactly why poor sleep is linked to cognitive decline, they say experimental evidence supports the theory that "sleep helps our brains flush out harmful proteins that build up during the day - such as amyloid beta - and are thought to cause dementia". Sleep depends on our minds' ability to dispose of it, "even in the brains of healthy people."

As for the association of long sleep with cognitive decline as well, previous studies have found a link between excessive sleep and cognitive performance, in terms of poor executive functions of the brain, such as the ability to remember events, speed of reaction and flexibility of thinking, but most of them remained dependent on the participants’ self-report of the duration of their sleep. At night, without the use of EEG devices, until this new study came to corroborate these results.

The quality of sleep is more important than the duration

What is surprising in the results of this study is that the ideal period of sleep that I set is no more than 6.5 hours, and she said that what exceeded that was associated with cognitive decline over time, that duration was much shorter than that emphasized by most of the previous recommendations for years, which is Adults are advised to get between 7 to 9 hours of sleep each night.

The reason for this development may be the researchers' view that "when it comes to the risk of developing dementia, it is not the length of sleep that matters, but the quality of sleep that matters."

For example, the study showed that cognitive impairment in particular, increases due to the lack of access to the stage of slow-wave sleep, a stage that receives special attention from scientists who are looking at ways to benefit from sleep in the best possible way.

According to Dr. Jan Born, Head of the Department of Medical Psychology and Behavioral Neuroscience, at a German university.

The stage is characterized by the deepest sleep, achieving the highest level of delta wave activity, with a significant decrease in brain and muscle activity, greater loss of response to external stimuli, and a decrease in levels of the stress hormone "cortisol", helping to activate the immune system to become more able to face any possible infection, and lowering Heart rate and breathing are at their lowest.

Study: The ideal sleep duration is set to no more than 6.5 hours (Getty Images)

Other factors that may affect the quality of our sleep

The study notes the importance of taking into account other factors - which can affect the quality of our sleep, and may be linked to dementia.

Such as poor health, socioeconomic status, or levels of physical activity.

Taken together, all of these factors may explain why longer sleep is associated with cognitive decline, as well as some factors that cannot be prevented, such as genetic predisposition.

There are many things we can do in parallel with getting a good night's sleep to help reduce the risk of dementia, such as exercising and eating a healthy diet.

While emphasizing that the researchers in this study said that "the ideal amount of sleep is between 4.5 and 6.5 hours each night," does not mean that "laying down for longer on the weekends may cause any damage to your brain," says Gregg. Elder, Lecturer in Psychology and Associate in Sleep Research, Northumbria University, Newcastle.