The Importance of Sleep for Brain Health

We all get it—sleep is essential for our well-being. But, surprisingly, its role might run deeper than many realize.

Research has shown that as we age, inadequate slow-wave sleep could heighten the risk of developing dementia. A 2023 study indicated that individuals over 60 may face a 27 percent increased risk of dementia if they lose even 1 percent of this essential deep sleep annually.

Slow-wave sleep, which is the third phase of our 90-minute sleep cycle, typically lasts around 20 to 40 minutes. It’s marked by reduced brain activity, lowered heart rate, and decreased blood pressure, making it the most rejuvenating stage of sleep. During this time, our bodies work to strengthen muscles, bones, and even immune responses while prepping our minds to absorb more information.

In another recent study, it was noted that people with Alzheimer’s-related brain changes performed better on memory assessments when they had more slow-wave sleep. Matthew Pase, a neuroscientist at Monash University in Australia, stated, “Slow-wave sleep supports the aging brain in many ways and helps clear metabolic waste, including harmful proteins associated with Alzheimer’s.” He added that their findings imply that the loss of slow-wave sleep might be a modifiable risk factor for dementia.

To explore this further, Pase and a team from Australia, Canada, and the US studied 346 participants from the Framingham Heart Study who underwent two overnight sleep assessments between 1995-1998 and again between 2001-2003, an average five years apart. At the later assessment, these participants were all over 60 and had no dementia records at the time.

Over 17 years of follow-ups, researchers recorded 52 cases of dementia among these individuals. They examined the results of the sleep studies to see how changes in slow-wave sleep correlated with the eventual incidence of dementia.

Interestingly, as participants aged, the amount of slow-wave sleep they experienced diminished, peaking around ages 75 to 80 before stabilizing. The research revealed a stark connection: every percentage point decline in slow-wave sleep per year corresponded to a 27 percent greater chance of developing dementia. This risk escalated to 32 percent when focusing specifically on Alzheimer’s.

The Framingham Heart Study has been instrumental in tracking various health indicators over time, including markers tied to early signs of Alzheimer’s and cardiovascular risks. They found that low slow-wave sleep levels as well as certain medications and the presence of the APOE ε4 gene—associated with Alzheimer’s—were linked both to increased cardiovascular disease risk and accelerated declines in sleep quality.

However, it’s worth noting that while these associations are clear, they do not definitively establish that the loss of slow-wave sleep causes dementia. It’s just as plausible that brain processes linked to dementia contribute to sleep disturbances, and more research is needed to clarify these relationships.

In the meantime, it’s crucial to prioritize good sleep habits. Taking steps to enhance your chances of achieving more of that all-important slow-wave sleep can go a long way toward supporting cognitive health.

The findings from this study were published in JAMA Neurology.