A recent study reveals that insufficient slow-wave sleep may elevate the risk of dementia in older adults. The research indicates that individuals over 60 years old who lose just 1 percent of this deep sleep each year face a 27 percent higher chance of developing dementia.
Slow-wave sleep, which occurs during the third stage of the body’s 90-minute sleep cycle, lasts approximately 20 to 40 minutes. This stage is crucial for rest, as brain waves and heart rate slow down, leading to lower blood pressure.
Deep sleep plays a vital role in strengthening muscles, bones, and the immune system while also helping the brain retain more information. Notably, recent findings suggest that individuals showing early signs of Alzheimer’s disease performed better on memory tests when they experienced more slow-wave sleep.
Matthew Pase, a neuroscientist at Monash University in Australia, stated, “Slow-wave sleep, or deep sleep, supports the aging brain in many ways. We know that sleep enhances the removal of metabolic waste from the brain, including proteins associated with Alzheimer’s disease.” He added, “Our findings suggest that slow-wave sleep loss may be a modifiable dementia risk factor.”
Pase and his colleagues from Australia, Canada, and the United States studied 346 participants from the Framingham Heart Study. These individuals completed two overnight sleep studies between 1995 and 1998 and again between 2001 and 2003, with an average five-year gap between tests.
The participants, all over 60 years old in 2020 and without a dementia diagnosis at the time of the second study, provided researchers with data to examine the relationship between sleep patterns and dementia risk over time. “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,” Pase explained.
Over the 17-year follow-up, researchers recorded 52 cases of dementia among the participants. They analyzed the participants’ slow-wave sleep levels from the sleep studies to identify any correlation with dementia.
Results showed a general decline in slow-wave sleep starting at age 60, peaking between 75 and 80 before leveling off. Each percentage point decrease in slow-wave sleep per year corresponded to a 27 percent increased risk of developing dementia, rising to 32 percent for Alzheimer’s disease specifically.
The Framingham Heart Study tracks various health metrics, including hippocampal volume loss, an early indicator of Alzheimer’s disease, as well as common factors that contribute to cardiovascular disease. The researchers found that lower levels of slow-wave sleep were associated with a higher risk of cardiovascular issues, certain medications affecting sleep, and the presence of the APOE ε4 gene, which is linked to Alzheimer’s.
“We discovered that a genetic risk factor for Alzheimer’s disease, rather than brain volume, was associated with accelerated declines in slow-wave sleep,” Pase noted.
While these findings establish a clear connection, the researchers caution that the study does not prove that slow-wave sleep loss directly causes dementia. It is possible that brain processes related to dementia could lead to sleep disruptions. More research is necessary to fully understand these factors.
In the meantime, prioritizing sufficient sleep is essential, as it benefits memory and overall health. There are also steps individuals can take to increase their chances of achieving more restorative slow-wave sleep.
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