People who spend less of the night in deep sleep and REM sleep may see measurable shrinkage in a brain area hit early in Alzheimer's disease.
A long-term US cohort study of 270 adults with a median age of 61 reports the link.
The team recorded participants' sleep in a lab and returned 13 to 17 years later for brain MRI scans.
Those with lower shares of deep sleep and REM sleep had smaller volumes in the inferior parietal region.
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That area helps the brain pull together different kinds of sensory information, including what the eyes see and where things are in space.
"Our findings suggest that a person’s overnight sleep architecture could be used as a potential marker for identifying people who may have an increased risk of Alzheimer’s disease-related brain atrophy," said lead author Gawon Cho, a postdoctoral associate at Yale School of Medicine.
The two sleep stages that seem to matter
Slow-wave sleep is the heavy, restorative stage of non-REM sleep that dominates the first half of the night.
Breathing slows, muscles relax and the brain's electrical activity slides into long, rolling waves.
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REM sleep, which comes in later cycles, is the stage when most vivid dreaming happens.
During REM the brain is highly active and helps consolidate memory.
Habits that support both stages
The sleep habits that support both stages are the ones the CDC has long recommended.
Go to bed and get up at the same time every day, weekends included.
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Keep the bedroom quiet, dark and cool. Avoid heavy meals and alcohol before bedtime, and skip caffeine in the afternoon or evening.
A second study points the same way
A separate longitudinal study, published in Alzheimer's & Dementia in 2026, lends weight to the link.
Researchers followed 326 older adults enrolled in the 1Florida Alzheimer's Disease Research Center and used the Pittsburgh Sleep Quality Index to gauge how well they slept.
Longer sleep duration and later wake times were tied to worse scores on a standard measure of cognitive and functional decline.
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The effect was stronger in participants who already showed elevated amyloid, elevated tau or smaller hippocampi, the brain's memory hub.
Why midlife sleep matters
Alzheimer's does not start on the day symptoms appear.
The disease's protein deposits, amyloid plaques and tau tangles, can build in the brain for up to 20 years before memory problems begin.
That gap is what makes midlife sleep habits a plausible prevention lever, not a lost cause.
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The 270-participant study is observational, so it cannot prove that thin deep sleep causes the shrinkage.
Other factors that disturb sleep, from untreated apnea to chronic pain, could drive both.
Even so, the two studies point in the same direction, and the practical habits that support deep sleep carry no downside.
For adults, the CDC recommends 7 or more hours of sleep each night, with the same bedtime and wake time on weekdays and weekends. Adults 65 and older need 7 to 8.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.