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For decades, the brain was thought to lack a dedicated waste-clearance system. Unlike the rest of the body, which relies on the lymphatic system to remove toxins and metabolic by-products, the brain appeared to have no equivalent mechanism. That assumption has now been overturned. In the last decade, researchers have identified the glymphatic system – a specialised clearance pathway that plays a critical role in brain health, ageing and neurodegenerative disease.
Understanding how the glymphatic system works, why it matters and how we can support it may prove central to preventing conditions such as Alzheimer’s disease and other forms of dementia.
What is the glymphatic system?
The glymphatic system is a network that clears waste products from the brain using cerebrospinal fluid (CSF). CSF is a clear, colourless fluid that surrounds the brain and spinal cord, acting as a protective cushion while delivering nutrients and removing metabolic waste. Because the brain is enclosed within the rigid structure of the skull, waste products cannot simply disperse – they must be actively flushed away.
The glymphatic system achieves this by circulating CSF through the spaces between brain cells, washing away toxins and metabolic by-products before draining them out of the central nervous system. If this clearance process is impaired, waste can accumulate, contributing to inflammation, disrupted neural communication and neurodegeneration.
Its name reflects its hybrid nature: “glial” cells (supporting cells in the brain) combined with a lymphatic-like function. Astrocytes, a type of glial cell, play a key role by regulating fluid movement through specialised water channels known as aquaporin-4.
Crucially, the glymphatic system is most active during sleep, particularly deep, slow-wave sleep. During this phase, brain cells shrink slightly, increasing the space between them and allowing CSF to flow more freely. This nightly flushing process removes potentially harmful proteins, including amyloid beta and tau, both of which are strongly linked to Alzheimer’s disease.
Why the glymphatic system matters
Every waking moment, brain cells produce waste as a by-product of normal metabolism. If this waste is not efficiently cleared, it accumulates. Over time, this build-up is thought to contribute to inflammation, impaired neural communication and neurodegeneration.
Research has increasingly linked impaired glymphatic function to:
- Alzheimer’s disease
- Other forms of dementia
- Traumatic brain injury
- Stroke
- Parkinson’s disease
- Cognitive decline associated with ageing
Recent large-scale imaging studies have shown that people with markers of reduced glymphatic activity are at a higher risk of developing dementia later in life. These findings reinforce the idea that dementia is not caused by a single factor, but by a complex interaction between sleep quality, vascular health and brain clearance mechanisms.
Rather than being purely a disease of memory, dementia may in part reflect a failure of the brain’s housekeeping systems.
Sleep: the cornerstone of glymphatic health
Sleep is not simply rest; it is an active biological state during which essential maintenance occurs. The glymphatic system relies on sleep to function properly, and chronic sleep disruption can significantly impair toxin clearance.
Studies have shown that even short periods of sleep deprivation can reduce the brain’s ability to remove amyloid beta. Over years, poor sleep may allow these proteins to accumulate, increasing dementia risk.
Conditions such as insomnia, fragmented sleep and obstructive sleep apnoea are therefore of particular concern. Sleep apnoea, in particular, disrupts deep sleep and alters intracranial pressure dynamics, further impairing glymphatic flow.
The role of cardiovascular and vascular health
The glymphatic system depends not only on sleep, but also on healthy blood vessels. CSF movement is partly driven by the pulsation of arteries within the brain. When vascular health is compromised – through high blood pressure, diabetes, atherosclerosis or reduced arterial elasticity – this pulsatile force weakens.
As a result, glymphatic clearance becomes less efficient.
This connection helps explain why cardiovascular risk factors are also dementia risk factors. The brain does not exist in isolation; its health is inseparable from the health of the heart and circulatory system.
Ageing and the glymphatic system
Glymphatic efficiency naturally declines with age. Changes in sleep architecture, reduced deep sleep, stiffening of blood vessels and altered aquaporin-4 function all contribute to reduced clearance capacity.
However, while ageing is unavoidable, accelerated decline is not. Lifestyle factors appear to play a meaningful role in preserving glymphatic function well into later life.
How can we support glymphatic function?
While research is ongoing, current evidence suggests several practical strategies that may help optimise glymphatic clearance:
- Prioritise high-quality sleep
Aim for consistent sleep schedules and sufficient duration, with an emphasis on deep, restorative sleep. Address sleep disorders early, particularly insomnia and sleep apnoea. - Support cardiovascular health
Maintain healthy blood pressure, manage cholesterol and blood sugar levels, and engage in regular aerobic exercise. These measures improve vascular elasticity and CSF movement. - Exercise regularly
Physical activity enhances circulation, supports arterial pulsatility and has been shown to improve sleep quality — a dual benefit for glymphatic function. - Stay hydrated
Adequate hydration supports CSF production and circulation. Chronic dehydration may impair clearance efficiency. - Moderate alcohol intake
Excessive alcohol has been shown to disrupt sleep and impair glymphatic flow. Moderation appears key. - Consider sleep posture
Some studies suggest that side sleeping may facilitate more efficient glymphatic drainage compared to sleeping on the back or stomach, though more research is needed.
A new way of thinking about dementia
The discovery of the glymphatic system represents a shift in how we understand brain health and neurodegenerative disease. Rather than focusing solely on late-stage pathology, it opens the door to prevention, maintenance and systems-based care.
This perspective is explored in depth by Dr Steve Allder, consultant neurologist at Re:Cognition Health, in his TEDx Talk Reimagining Dementia. In the talk, Dr Allder challenges traditional, memory-centric models of dementia and highlights the importance of sleep, brain clearance and whole-system health in reducing risk and supporting cognitive resilience.
By reframing dementia as a condition influenced by modifiable biological processes, including the glymphatic system, we move closer to proactive strategies that protect brain health across the lifespan.
The Future of Brain Health and Dementia Prevention
While many questions remain, one message is clear: sleep is not optional for brain health. The glymphatic system reminds us that the brain requires time, space and the right physiological conditions to clean, repair and protect itself.
As research continues to evolve, supporting glymphatic function may become one of the most powerful (and accessible) tools we have to safeguard cognitive health, slow brain ageing and reduce the burden of neurodegenerative disease.
