Scientists reveal: One stage of sleep is key to reducing the risk of dementia

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The risk of getting dementia can increase with age, if we do not sleep in so-called deep sleep. The results of the new study showed that in people over the age of 60, the risk of developing dementia is 27 percent higher if they lose just 1 percent of this sleep phase per year, writes "Science Alert".

Deep sleep is the third stage of the 90-minute human sleep cycle. This phase, which is the calmest, lasts about 20 to 40 minutes, and then brain waves and heart rate slow down while blood pressure drops.

This type of sleep strengthens our muscles, bones and immune system and prepares the brain to absorb more information. Now, scientists have found that individuals with brain changes associated with Alzheimer's disease performed better on memory tests when they slept more deeply.

"Slow-wave sleep, or deep sleep, helps the aging brain in many ways, and we also know that sleep increases the removal of metabolic waste from the brain, including facilitating the removal of proteins that build up in Alzheimer's disease." However, until now we were not sure what role slow-wave sleep played in the development of dementia. Our findings suggest that loss of slow-wave sleep may be a risk factor for dementia," says Australian neuroscientist Matthew Pass.

In the study, Matthew Pass and colleagues from Australia, Canada and the United States examined 346 participants who took part in two sleep studies between 1995 and 1998 and between 2001 and 2003, with an average of five years between testing periods.

Among the members of this group, dementia was not registered at the time of the study in 2001-2003. Also, respondents were over 60 years old in 2020.

Analyzing their data, the researchers were able to look at the relationship between the two factors over time, comparing datasets from two in-depth polysomnography sleep studies and then tracking participants' dementia through 2018.

"We used them to examine how deep sleep changes with aging and whether changes in the proportion of slow-wave sleep, namely deep sleep, might be associated with the risk of developing dementia later in life, up to 17 years later," Passe said. .

During the 17-year follow-up, 52 cases of dementia were observed among the participants. The deep sleep of the participants was also observed in all the studies, and now the data was analyzed to see if there was a connection with the onset of dementia.

Overall, the time spent in deep sleep was found to decrease from age 60 onwards, with the decline being greatest between ages 75 and 80, before leveling off thereafter.

Comparing data from the two studies, the researchers found a link between each percentage point decrease in slow-wave sleep per year and a 27 percent increased risk of developing dementia. That risk rose to 32 percent when they focused on Alzheimer's disease, the most common form of dementia.

The study looked at multiple health data over time, including loss of hippocampal volume (an early sign of Alzheimer's disease) and common factors that contribute to the development of cardiovascular disease.

"We found that a genetic risk factor for Alzheimer's disease, but not brain volume, was associated with an accelerated decline in time spent in deep sleep," says Pass.

Although these are clear associations, the authors note that this type of study does not prove that the loss, or lower amount, of deep sleep causes dementia, and it is possible that dementia-related brain processes cause sleep loss. More research is needed to fully understand these factors.

Of course, until scientists come up with new knowledge, we can prioritize quality sleep and get enough time for sleep, because it is important for many things, not just improving memory.

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