A new study suggests that the type of sleep a person gets may be more important for long-term brain health than the total number of hours spent asleep. Researchers found that adults who spent less time in deep sleep and REM sleep were more likely to show shrinkage in brain regions that are often affected early in Alzheimer’s disease. The study followed 270 middle-aged and older adults, most in their early 60s, for over a decade.
At the start of the study, each participant underwent an overnight sleep study to measure time spent in slow wave sleep, also called deep sleep, and REM sleep. About 13 to 17 years later, the same participants received brain scans to measure the size of specific brain regions known to be vulnerable in Alzheimer’s disease. These areas include the inferior parietal lobule and precuneus, which are involved in memory, attention, and spatial reasoning.
The results showed a clear link. People who had less deep sleep had smaller volumes in the inferior parietal and cuneus regions. Those who had less REM sleep had smaller volumes in the inferior parietal and precuneus areas. The study did not prove that poor sleep caused the brain changes, but the connection was strong enough to raise concern. These brain regions are among the first to decline as Alzheimer’s progresses.
The findings build on earlier research. Previous studies have shown that deep sleep helps clear waste from the brain, including beta-amyloid, a protein that builds up in Alzheimer’s. One study found that a single night of disrupted deep sleep led to increased beta-amyloid accumulation. Other research suggests that slow wave sleep supports the glymphatic system, which acts as a cleaning system for the brain.
While people cannot fully control how much REM or deep sleep they get, certain habits may help. Going to bed and waking up at the same time each day supports better sleep cycling. Avoiding caffeine late in the day is also important, as caffeine close to bedtime can suppress deep sleep. Getting morning sunlight helps anchor the body’s circadian rhythm, which can improve sleep quality and structure. Regular exercise, including aerobic and resistance training, has been shown to increase the proportion of deep sleep and REM sleep over time. Limiting alcohol close to bedtime is also recommended, as alcohol has a negative effect on REM sleep later in the night.
This study adds to a growing body of evidence that sleep quality can influence brain health years or even decades later. Sleep is a modifiable factor, meaning people can take steps to support their cognitive future by improving the quality and composition of their sleep now. The researchers emphasize that quality rest is not a luxury but an important part of protecting brain health.
