A new study published in the Journal of Clinical Sleep Medicine has revealed compelling evidence that poor sleep may contribute to brain shrinkage in areas commonly affected by Alzheimer’s disease. The findings suggest that reduced time spent in key sleep phases—particularly slow-wave and REM (rapid-eye movement) sleep—may play a critical role in the brain changes associated with the progression of this neurodegenerative condition.

Scientists have long suspected a link between sleep and Alzheimer’s, but this latest research takes a more detailed look at how specific sleep stages relate to changes in brain structure. The researchers focused on sleep architecture, which refers to the pattern and quality of sleep stages that the brain cycles through each night. These phases include light sleep, deep slow-wave sleep, and REM sleep—the stage associated with dreaming and memory consolidation.

The study followed 270 older adults who were part of the Atherosclerosis Risk in Communities Study. Participants initially underwent polysomnography, a comprehensive sleep study that recorded their sleep patterns. More than a decade later, they underwent MRI scans to evaluate changes in their brain structure. The researchers specifically looked at brain regions that are known to shrink in the early stages of Alzheimer’s, such as the inferior parietal region, precuneus, and cuneus.

The results showed that individuals who spent less time in slow-wave sleep had smaller volumes in the inferior parietal region and the cuneus. Similarly, those with reduced REM sleep also had smaller volumes in the inferior parietal and precuneus regions. After adjusting for other potential factors, the strongest association was between reduced slow-wave and REM sleep and shrinkage in the inferior parietal region. Interestingly, frequent nighttime awakenings and the presence of cerebral microbleeds—tiny bleeds in the brain often linked with Alzheimer's—did not appear to affect brain volume in these areas.

The findings offer insight into why poor sleep may increase the risk of Alzheimer’s. One explanation lies in the brain's waste removal system, known as the glymphatic system, which becomes highly active during slow-wave sleep. This system helps flush out toxic proteins like beta-amyloid and tau, which are known to accumulate in the brains of people with Alzheimer’s. Without sufficient slow-wave sleep, these harmful substances may build up over time.

Dr. Chelsie Rohrscheib, a neuroscientist and sleep consultant who was not involved in the study, explained that sleep plays a vital role in brain maintenance, learning, memory, and clearing waste. She emphasized that many of these critical processes occur specifically during slow-wave and REM sleep. Dr. Leah Kaylor, a psychologist specializing in sleep, added that during sleep, the brain slightly shrinks, allowing cerebrospinal fluid to flow through and remove accumulated waste products—a process she likened to a “car wash” for the brain.

Though the study provides important insights, the researchers note that their sample size was limited and lacked diversity. More research is needed to fully understand the long-term effects of sleep architecture on brain health across various populations. However, the study's 13–17-year follow-up adds weight to the idea that changes in sleep may not just be a symptom of Alzheimer’s but potentially a contributing factor.

While scientists continue to investigate the underlying mechanisms of Alzheimer’s, the message from this research is clear: getting enough deep, restorative sleep may be more important than ever for maintaining brain health and reducing the risk of neurodegenerative disease.