A new study suggests that the quality of sleep, specifically the time spent in deep and REM stages, may be more important for long-term brain health than the total number of hours slept.
Researchers analyzed data from 270 middle-aged and older adults, most in their early 60s at the study’s start. Each participant completed an overnight sleep study to measure time spent in different sleep stages, including slow wave (deep) sleep and REM sleep.
Approximately 13 to 17 years later, the same participants received brain scans. The scans focused on the size of specific brain regions known to be vulnerable in Alzheimer’s disease, such as the inferior parietal lobule and precuneus. These areas are involved in memory, attention, and spatial reasoning.
The study found a link between sleep quality from years earlier and brain volume. People who spent less time in slow wave and REM sleep were more likely to show shrinkage in brain regions associated with early Alzheimer’s. 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 causes brain changes, but the association was strong. These findings build on previous research showing that deep sleep helps clear waste from the brain, including beta-amyloid, a protein that builds up in Alzheimer’s. One earlier study found that a single night of disrupted deep sleep led to increased beta-amyloid accumulation.
While people cannot fully control their sleep stages, some habits may help improve sleep architecture. Sleep consistency, going to bed and waking up at the same time daily, supports better sleep cycling. Avoiding caffeine too close to bedtime can help, as it can suppress deep sleep. Getting morning sunlight helps anchor the circadian rhythm. Regular exercise, including aerobic and resistance training, has been shown to increase the proportion of slow wave and REM sleep over time. Limiting alcohol close to bed is also recommended due to its negative effect on REM sleep.
This study adds to the evidence that sleep quality can influence brain health over many years. Sleep is a modifiable factor, meaning people can support their cognitive future by improving the quality and composition of their sleep now.
