It’s widely recognized that a good night’s sleep is essential for our overall health, but its significance extends beyond basic well-being.
Research indicates that the risk of dementia increases as people age if they fail to get sufficient slow-wave sleep.
A study conducted in 2023 revealed that individuals over 60 are 27 percent more likely to develop dementia if they lose just 1 percent of this deep sleep annually.
Slow-wave sleep is the third stage of the human 90-minute sleep cycle, lasting approximately 20–40 minutes. It is the most restorative stage, characterized by a slowing of brain waves and heart rate, as well as a drop in blood pressure.
This stage of deep sleep enhances muscle, bone, and immune system strength, while also preparing the brain to absorb new information.
Another recent study found that individuals with Alzheimer’s-related brain changes performed better on memory tests when they experienced more slow-wave sleep.
“Slow-wave sleep, or deep sleep, supports the aging brain in many ways, and we know that sleep augments the clearance of metabolic waste from the brain, including facilitating the clearance of proteins that aggregate in Alzheimer’s disease,” said neuroscientist Matthew Pase from Monash University in Australia.
“However, to date we have been unsure of the role of slow-wave sleep in the development of dementia. Our findings suggest that slow-wave sleep loss may be a modifiable dementia risk factor.”
Pase and his team from Australia, Canada, and the US analyzed 346 participants from the Framingham Heart Study who had undergone two overnight sleep studies between 1995 and 1998, and between 2001 and 2003, with about five years between the two periods.
This community-based group, who had no dementia history during the 2001-2003 study and were over 60 by 2020, allowed researchers to explore the connection between two factors over time by comparing data from the two detailed polysomnography sleep studies and then monitoring dementia incidence among participants until 2018.
“We used these to examine how slow-wave sleep changed with aging and whether changes in slow-wave sleep percentage were associated with the risk of later-life dementia up to 17 years later,” said Pase.
Over the 17 years of follow-up, 52 cases of dementia were identified among the participants. Researchers also examined the participants’ slow-wave sleep levels recorded in the sleep studies for any connections to dementia cases.
Overall, the rate of slow-wave sleep was observed to decrease from age 60 onward, with this decline peaking between ages 75 and 80, before stabilizing.
By comparing the initial and subsequent sleep studies, researchers identified a link between each annual percentage point decrease in slow-wave sleep and a 27 percent increased risk of developing dementia.
This risk increased to 32 percent when focusing on Alzheimer’s disease, the most prevalent form of dementia.
The Framingham Heart Study tracks various health metrics over time, including hippocampal volume loss (an early indicator of Alzheimer’s) and common cardiovascular disease risk factors.
Low levels of slow-wave sleep were associated with a higher risk of cardiovascular disease, medications affecting sleep, and the presence of the APOE ε4 gene, which is linked to Alzheimer’s.
“We found that a genetic risk factor for Alzheimer’s disease, but not brain volume, was associated with accelerated declines in slow-wave sleep,” Pase said.
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While these associations are clear, the authors emphasize that this type of study does not prove that slow-wave sleep loss causes dementia, as dementia-related brain processes might also lead to sleep loss. More research is needed to fully understand these factors.
In the meantime, prioritizing sufficient sleep is crucial for more than just memory enhancement.
There are even strategies you can adopt to increase the amount of this essential slow-wave sleep.
The study is published in JAMA Neurology.
An earlier version of this article was published in November 2023.
