A new study suggests that the quality of sleep, specifically the time spent in deep and REM sleep, may be more important for long-term brain health than the total number of hours slept. Researchers followed 270 middle-aged and older adults, most in their early 60s, for over a decade.
At the start of the study, each participant had an overnight sleep study to measure how much time they spent in different sleep stages, including slow wave sleep, also known as deep sleep, and REM sleep. Between 13 and 17 years later, the same participants received brain scans to measure the size of brain regions known to be vulnerable in Alzheimer’s disease. These areas include the inferior parietal lobule and precuneus, which are key for memory, attention, and spatial reasoning.
The study found that people who got less slow wave and REM sleep were more likely to have shrinkage in these brain regions. Specifically, less deep sleep was tied to smaller volumes in the inferior parietal and cuneus regions. Less REM sleep was linked to smaller volumes in the inferior parietal and precuneus areas. The study did not prove that poor sleep caused the brain changes, but the association was strong, especially since these regions are among the first to decline in Alzheimer’s disease.
These findings build on earlier research showing that deep sleep helps clear waste from the brain, such as beta-amyloid, a protein that builds up in Alzheimer’s. One previous study found that even a single night of disrupted deep sleep led to increased beta-amyloid accumulation. Other research shows that slow-wave sleep supports the glymphatic system, a process that may help prevent neurodegeneration.
While people cannot fully control how much REM or slow wave sleep they get, some habits may help improve sleep architecture. Going to bed and waking up at the same time daily supports better sleep cycling. Avoiding caffeine too close to bedtime can help, as caffeine can suppress deep sleep. Getting morning sunlight helps anchor the circadian rhythm, which can improve sleep quality and structure. Regular aerobic and resistance training have been shown to increase the proportion of slow wave sleep and REM over time. Limiting alcohol close to bed is also recommended, as it negatively affects REM sleep later in the night.
The study serves as evidence that how a person sleeps could influence brain health years later. Sleep is a modifiable factor, meaning people can support their cognitive future by improving the quality and composition of their sleep now.
