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A team of researchers from Australia, the United States, and Canada has found that the third stage of sleep—known as slow-wave sleep—plays a crucial role in reducing the risk of dementia. According to their study, individuals over the age of 60 are 27 percent more likely to develop dementia if they lose just 1 percent of their slow-wave sleep each year.
Previous studies have shown that deep sleep is essential for strengthening muscles, bones, and the immune system, as well as preparing our brains to absorb more information.
Slow-wave sleep is the third stage of the human sleep cycle; it typically begins about 40 minutes after falling asleep and lasts for approximately 20 to 40 minutes. This is a calm phase of the deepest sleep, during which brain wave activity and heart rate slow down, and blood pressure decreases. Sleep scientists also distinguish between the lightest sleep stage, where a person can wake up quickly (Stage 1), Stage 2 of light sleep (NREM), which lasts nearly half of the entire cycle, and Stage 4, REM sleep, during which we dream.
What Scientists Discovered
Thus, the risk of developing dementia increases with age if a person does not get enough slow-wave sleep.
“Slow-wave or deep sleep protects the brain from aging, enhances the removal of metabolic waste from the brain, and helps eliminate proteins that aggregate in Alzheimer’s disease,” noted neurobiologist Matthew Pace, the lead author of the study from Monash University in Australia.
Pace’s team studied sleep data from 346 volunteers between 1995 and 1998 and again from 2001 to 2003.
During the 2001-2003 study, researchers did not record any cases of dementia among participants. However, in 2020, when the volunteers were over 60 years old, the scientists obtained some intriguing results, as reported by Science Alert. They first examined how slow-wave sleep changed in participants as they aged and then linked these changes to the development of dementia in older age.
The team noticed that after the age of 60, the duration of slow-wave sleep in participants began to significantly decrease. This decline peaked between the ages of 75 and 80, after which the situation regarding deep sleep stabilized.
After 2003, 52 cases of dementia were recorded among the participants.
The team found a connection between the annual reduction in the duration of slow-wave sleep and a 27 percent increase in the risk of developing dementia. In the case of Alzheimer’s disease, the most common form of dementia, this risk jumped to 32 percent.
Researchers also noted that poor quality of slow-wave sleep correlates with a higher likelihood of cardiovascular diseases, the use of sleep-disrupting medications, and the presence of the APOE ε4 gene, which is associated with Alzheimer’s disease.
The study’s findings were published in JAMA Neurology.
