The same system that helps clean the brain during deep sleep may also provide clues about why disrupted sleep is linked to cognitive decline and neurological disease.
Sleep is increasingly recognized as more than a period of rest.
During sleep, the brain carries out important maintenance processes, including the activation of the glymphatic system, a waste-clearance pathway that helps remove substances produced during normal brain activity.
Scientists are now investigating whether problems with this nighttime cleaning system may contribute to the development or progression of neurological disorders.
Impaired glymphatic clearance has been observed or proposed in several conditions, including Alzheimer’s disease, Parkinson’s disease, traumatic brain injury, and some psychiatric disorders.
Many of these conditions are also associated with disrupted sleep, suggesting that sleep and brain health may influence one another in complex ways.
The strongest evidence so far comes from research examining the relationship between sleep, the glymphatic system, and Alzheimer’s disease.
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Sleep and the Brain’s Waste Products
One important substance involved in Alzheimer’s disease research is amyloid-beta, a protein that can accumulate in the brain when clearance processes become impaired.
Studies in both mice and humans have shown that amyloid-beta levels naturally fluctuate across the day.
Levels tend to increase during periods of wakefulness and decrease during sleep, suggesting that sleep provides an opportunity for the brain to remove this waste product.
However, when sleep is disrupted, this natural rhythm may be affected.
In mouse models of Alzheimer’s disease, impaired sleep is associated with a disruption of these normal daily fluctuations in amyloid-beta levels.
Researchers have also found that experimentally reducing sleep can increase levels of both amyloid-beta and tau proteins in the brain.
These findings suggest that insufficient sleep may interfere with the brain’s ability to maintain a healthy balance of proteins involved in neurodegeneration.
What Happens as We Age?
The relationship between sleep and brain cleansing becomes especially important as we grow older.
Deep non-rapid eye movement (NREM) sleep, the stage most strongly associated with glymphatic activity, naturally declines with age.
Researchers have also observed reductions in cerebrospinal fluid movement, which is associated with glymphatic function, as people move from healthy aging toward mild cognitive impairment and Alzheimer’s disease.
This raises an important question:
Could protecting healthy sleep patterns help support brain health throughout aging?
Scientists are still working to understand the answer.
Sleep disruption is only one factor among many that influence Alzheimer’s disease risk, and researchers are continuing to investigate how sleep, genetics, lifestyle, and other biological processes interact.
A Two-Way Relationship
The connection between sleep and brain health appears to work in both directions.
Poor sleep may contribute to reduced brain maintenance by limiting the time available for processes such as glymphatic clearance.
At the same time, changes occurring during neurological disease may further disrupt sleep quality.
This creates a cycle in which impaired sleep and declining brain health may reinforce one another.
But research suggests that improving certain sleep disorders may have meaningful benefits.
For example, treating sleep apnea during midlife has been associated with delaying the onset of cognitive decline by more than a decade.
While scientists are still uncovering the details, these findings highlight an important possibility: supporting healthy sleep may be one way to support the brain’s natural protective systems.
Why This Matters
The discovery of the glymphatic system has changed how scientists understand sleep.
Sleep is not simply a time when the brain rests but a period of active biological maintenance.
Protecting deep, restorative sleep may be an important part of maintaining brain health across the lifespan.
As researchers continue to explore the relationship between sleep, the glymphatic system, and neurological disease, it’s becoming clear that a good night’s sleep may be doing far more for your brain than simply helping you feel rested the next day.
Excerpted and adapted from “The new science of sleep: From cells to large-scale societies” by Omer Sharon, et al. published in PLoS Biology, under the terms of the Creative Commons Attribution License CC BY 4.0.