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This One Sleep Habit Might Matter More Than Hours Slept For Cognitive Health
We’ve all felt the brain fog after a poor night’s sleep. But beyond the grogginess, research is now showing that consistently missing out on certain sleep stages, particularly deep and REM sleep, could affect your brain in lasting ways.
A new study followed adults for more than a decade and found that people who spent less time in slow wave (deep) sleep and REM sleep were more likely to show shrinkage in brain regions that tend to atrophy early in Alzheimer’s disease.
These findings build on a growing body of research connecting sleep and long-term cognitive health, adding another layer to the idea that how we sleep today shapes our mental sharpness tomorrow.
Let’s take a look at the study and, more importantly, how to support these restorative stages of sleep to protect your brain for the long haul.
How deep & REM sleep shape brain health over time
Researchers analyzed data from 270 middle-aged and older adults, most of whom were in their early 60s at the start of the study. Each participant underwent an overnight sleep study to measure how much time they spent in different sleep stages, like slow wave sleep (also called deep sleep) and REM sleep.
Then, around 13 to 17 years later, those same participants received brain scans to look at the size of specific regions known to be vulnerable in Alzheimer’s disease, like the inferior parietal lobule and precuneus. These areas are key players in memory, attention, and spatial reasoning—all functions that tend to decline early in dementia.
The researchers wanted to understand if there was a long-term relationship between the quality of someone’s sleep years ago and their brain volume today. And that’s exactly what they found.
Less quality sleep = smaller brain regions tied to Alzheimer’s
People who got less slow wave and REM sleep were more likely to have 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.
While this study didn’t prove that poor sleep caused the brain changes, the association was strong enough to raise concern, especially because these regions are among the first to decline in Alzheimer’s progression.
These findings build on previous studies that show how deep sleep plays a vital role in clearing out waste in the brain, like beta-amyloid, the protein that builds up in Alzheimer’s.
One study found that even a single night of disrupted deep sleep led to increased beta-amyloid accumulation1. Other research shows that slow-wave sleep supports the glymphatic system, a kind of “rinse cycle” for the brain that may help prevent neurodegeneration.
So, how can you improve your sleep architecture?
While we can’t yet control how much REM or SWS we get with total precision, a few well-supported habits may help:
- Prioritize sleep consistency: Going to bed and waking up at the same time daily supports better sleep cycling.
- Avoid late caffeine: Caffeine too close to bedtime can suppress deep sleep2. Aim to keep your caffeine intake in the first half of the day.
- Get morning sunlight: Early light exposure helps anchor your circadian rhythm, which can improve both sleep quality and structure.
- Exercise regularly: Aerobic and resistance training have been shown to increase the proportion of SWS and REM over time.
- Minimize alcohol: Limit alcohol close to bed due to its negative effect on REM sleep later in the night.3
RELATED READ: The 3 Best Non-Melatonin Sleep Aids Of 2025
The takeaway
This study is a compelling piece of evidence that how we sleep could influence the health of our brains years, even decades, down the line.
The most powerful part? Sleep is a modifiable factor. While we can’t change our genes or fully prevent age-related changes, we can support our cognitive future by improving the quality and composition of our sleep now.
In a culture that often glorifies busyness and late nights, this is your reminder: quality rest isn’t a luxury—it’s essential neuroprotection.