We often say that one of the most important functions of sleep is clearing waste from the brain. You may have wondered what that means or how it works. Kasia Gustaw Rothenberg, MD, PhD, the Director of Neuropsychiatric Services at Cleveland Clinic’s Center for Brain Health, explains the biological system that’s responsible for nighttime brain cleaning.
Read the interview with Dr. Rothenberg below.
WAM: Why is it important that we talk about cleaning the brain, or clearing out waste from the brain?
Dr. Rothenberg: The brain is one of the most metabolically active organs in the body, constantly producing waste as it works. Unlike other organs, it doesn’t have a traditional lymphatic system, so it relies on a specialized cleaning pathway. If this waste—especially proteins like beta-amyloid and tau—is not efficiently cleared, it can accumulate and contribute to neurodegenerative diseases such as Alzheimer’s disease. So “cleaning the brain” is not just a metaphor; it is a fundamental process for maintaining cognitive health and long-term brain resilience.
WAM: What is the glymphatic system and how does it work? Is this a nightly activity?
Dr. Rothenberg: The glymphatic system is the brain’s waste clearance system. It uses cerebrospinal fluid to flush out metabolic byproducts from brain tissue, moving along channels formed by glial cells, hence the name “glymphatic.”
This process is highly dynamic and primarily active during sleep. At night, brain cells slightly shrink, allowing fluid to circulate more freely and remove waste more efficiently. So yes, this is very much a nightly “cleaning cycle,” and its effectiveness depends on the quality of your sleep.
WAM: During what stage of sleep is the glymphatic system most active? How do we make sure we are getting enough of this type of sleep?
Dr. Rothenberg: The glymphatic system is most active during deep sleep, also known as slow-wave sleep. This is the most restorative phase of sleep, when brain activity slows and the conditions for waste clearance are optimal.
To support this stage of sleep, consistency is key. Maintaining a regular sleep schedule, minimizing alcohol and late-night screen exposure, managing stress, and creating a dark, quiet sleep environment all help. Physical activity during the day also promotes deeper sleep at night.
WAM: How does age affect the glymphatic system? Are there other conditions that might also impact the effectiveness of the system?
Dr. Rothenberg: As we age, the efficiency of the glymphatic system declines. Sleep becomes lighter and more fragmented, and the structural pathways that support fluid flow become less effective. This may contribute to the increased risk of protein accumulation seen in aging and Alzheimer’s disease.
Other factors can also impair this system, including vascular disease, hypertension, traumatic brain injury, and chronic sleep disorders such as sleep apnea. Even chronic stress can indirectly disrupt glymphatic function by impairing sleep quality.
WAM: What lifestyle changes might improve the functioning of the glymphatic system?
Dr. Rothenberg: The most powerful intervention is optimizing sleep—both duration and quality. Think of sleep as the brain’s essential maintenance window. Regular physical activity, cardiovascular health, and good blood pressure control all support glymphatic flow. Sleeping on your side may also enhance clearance compared to lying on your back. Equally important is reducing factors that disrupt sleep, such as untreated sleep apnea, excessive alcohol use, and chronic stress. Ultimately, protecting the glymphatic system is about protecting sleep and vascular health—two pillars of brain longevity.