How does your brain take out the trash?

Research has identified that poor removal of waste from the brain via the glymphatic system is implicated in various health problems. Yet comparatively little is known about this dedicated waste removal system and I knew nothing about it until recently coming across current research. The name ‘glymphatic’ is a reference to the glial cells of the brain and the lymphatic system, which are both vital to waste clearance. The glymphatic system also facilitates  brain-wide distribution of several compounds, including glucose, lipids, amino acids, growth factors, and neuromodulators so if we have poor glymphatic flow, we’re not going to be very healthy.

Whereas our lymphatic system is able to clear metabolic waste from interstitial spaces throughout our body, the central nervous system (CNS) has no true lymphatic vessels and, because it is so active, metabolic waste can rapidly build up; this is where the glymphatic system comes in. If the brain becomes overloaded with waste products or is slowed down as we age, this toxic metabolic waste will build up between cells. This waste includes β-amyloid and tau proteinsthat are linked to Alzheimer’s Disease.

Astroglia, a type of glial cell, are important. Receptors on these cells allow cerebrospinal fluid (CSF) to move into the CNS, creating a flow that shunts fluid through the system. CSF is a clear fluid that surrounds the CNS to protect it. The glymphatic system, which runs parallel to our arteries, also harnesses the pulsing of blood through vessels to help keep things moving; as the blood vessels expand rhythmically, they drive the exchange of compounds between the interstitial space and the CSF. Our glymphatic and lymphatic systems connect at the dura, which is the thick membrane of connective tissue that covers the CNS, from where waste can be taken up for removal.

Using a mouse model, a recent research study found the glymphatic system functions most efficiently in conjunction with the slow-wave electrical activity of the brain that occurs during deep sleep and is largely disengaged when awake. Sleep was shown to produce a significant increase in the exchange of CSF and interstitial fluid, thereby speeding the removal of waste, including β-amyloid and tau protein. Scientists suggest accumulation of these proteins in the brain indicates problems in the functioning of the glymphatic system. Researchers concluded the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the CNS when we are awake. It may be possible that too little deep sleep deters glymphatic clearance and could contribute to the development of neurological diseases. This assumption is supported by clinical observations that sleep disorders are associated with a heightened risk of developing Alzheimer’s disease.

Researchers are also investigating links between the glymphatic system and conditions such as high blood pressure. Using a mouse model of hypertension (raised blood pressure),researchers demonstrated that artery stiffening (induced by raised blood pressure) interfered with the way the waste disposal system worked, preventing efficient removal of large molecules from the brain, such as β-amyloid. It is suggested these findings might help explain why scientists have found linksbetween raised blood pressure, cognitive decline and dementia. A possible link between the glymphatic system and Parkinson’s disease is being investigated. This is another condition characterised by the build up of alpha-synuclein protein in the brain. Parkinson’s sufferers often experience sleep disturbances.

A certain level of cognitive decline is almost inevitable with ageing. Whilst a wide range of factors will be involved, some scientists believe the glymphatic system could play a role. A study using mice found a “dramatic decline in the efficiency” of the glymphatic system. Other research continues to investigate links with traumatic brain injury, ischemic and haemorrhagic stroke, and type 2 diabetes.

Apart from sound sleep, two other factors that form part of the basis of a naturopathic approach to health have been found to influence the glymphatic system. These are hydration and exercise.

Water is vital for all organs and systems of our body, including our brain, with dehydration having a negative influence on the delivery of nutrients via the circulatory system and removal of waste via the lymphatic system. Dehydration has a negative influence on both systems. Our brain is about 75% water so when adequately hydrated we should be able to think faster, be more focused and experience greater clarity. Water is essential for delivering nutrients to the brain (via the circulatory system) and removing toxins (via the glymphatic system). On average, aim for around 1.5 – 2 litres of fluid daily; as explained in the Natural Healthcare College course, certain factors may require us to drink a little more fluid. 2 – 3 drinks of tea and/or coffee can count in this total but ideally choose water, fruit or herb teas. Incidentally, alcohol isn’t considered a beneficial type of fluid so it can’t be included in this 1.5 – 2 litres. The body’s requirement for fluid is an important topic so the course covers it in detail, including explaining why drinking too much fluid can create health problems.

Regular exercise has been shown to promote memory, improve mood, and decrease anxiety. A study showed exercise can positively influence the function of the glymphatic system, suggesting increased glymphatic flow following exercise may be just what the brain needs to clear away debris and function optimally. People who sit and use their brains for long periods create more waste and at the same time have greatly reduced blood flow creating a shortage of cleansing fluids, thereby reducing the efficiency of the glymphatic system.

The glymphatic system might not contain the answers to all our questions about neurodegenerative diseases but it could hold the key to interesting new perspectives. There are simple steps we can take to help support the efficiency of our own glymphatic system – deep sleep, exercise, and an adequate daily intake of fluid.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803388/

https://www.helsinki.fi/en/news/health-news/deep-sleep-cleanses-the-brain

http://sitn.hms.harvard.edu/flash/2018/clearing-junk-healthy-lifestyle-choices-boost-brain-waste-disposal/

https://www.ncbi.nlm.nih.gov/pubmed/25947369

https://www.ncbi.nlm.nih.gov/pubmed/25204284

https://shcs.ucdavis.edu/blog/archive/healthy-habits/your-brain-h2o