What is the glymphatic system?
The glymphatic system is a brain-wide perivascular network that allows cerebrospinal fluid to flow along the outside of blood vessels before entering the brain itself through non-neuronal support cells called glial cells. The cerebrospinal fluid then acts a bit like a “soap” for the brain, mixing with interstitial fluid between neurons before being flushed back out of the brain and carrying away harmful metabolic waste products along with it.
Glymphatic clearance of metabolic waste is increased during sleep
During sleep, the interstitial spaces between neurons expand by approximately 60% allowing cerebrospinal fluid to flow through the brain and remove waste much more efficiently. The size of these interstitial spaces is regulated by a neurotransmitter called norepinephrine, which keeps brain cells slightly swollen and packed tightly together when you’re awake. Sleep triggers a reduction in norepinephrine that causes brain cells to shrink, thus increasing the space between these cells. Norepinephrine levels are at their lowest point during a specific stage of deep sleep known as slow-wave sleep, and it is during this phase that the brain does most of its cleaning.
Link between the glymphatic system and dementia
Among the harmful metabolic waste products cleared by the glymphatic system are two key proteins heavily associated with Alzheimer’s disease: amyloid-beta and tau. A recent review has suggested that at least 15% of Alzheimer’s disease cases could be attributed to chronic sleep disorders. Furthermore, sleep deprivation studies have shown that even a single night of sleep deprivation can significantly impair the glymphatic system’s ability to clear these neurotoxic proteins from the brain into the bloodstream. This results in increased protein accumulation in brain regions that are crucial for memory processing, including the hippocampus and thalamus. Therefore, making sure you get enough sleep each night is a good practical way to help protect your brain from the dangers of dementia.
References
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Xie L., et al. (2013). Sleep Drives Metabolite Clearance from the Adult Brain. Science, 342, 373-377. https://doi.org/10.1126/science.1241224
Dagum P., et al. (2026). The glymphatic system clears amyloid beta and tau from brain to plasma in humans. Nat. Commun., 17, 715. https://doi.org/10.1038/s41467-026-68374-8
Shokri-Kojori E., et al. (2018). β-Amyloid accumulation in the human brain after one night of sleep deprivation. Proc. Natl. Acad. Sci. U.S.A., 115(17), 4483-4488. https://doi.org/10.1073/pnas.1721694115
Zare F., et al. (2026). Sleep-Dependent Clearance of Brain Metabolites via the Glymphatic System: Implications for Alzheimer’s Pathophysiology. Brain and behavior, 16(4), e71374. https://doi.org/10.1002/brb3.71374
Corbali O. & Levey A. I. (2025). Glymphatic system in neurological disorders and implications for brain health. Frontiers in neurology, 16, 1543725. https://doi.org/10.3389/fneur.2025.1543725
