Problems with brain's waste clearance may increase risk of dementia: Study

An impaired movement of the brain's cerebrospinal fluid, which helps remove waste, could explain how poor sleep and heart conditions can increase one's risk of dementia, according to a study.

Other functions of the cerebrospinal fluid include cushioning the central nervous system from shocks and delivering nutrients. The colourless fluid is part of the glymphatic system.

Researchers led by those at the UK's University of Cambridge said the glymphatic system is considered important for protecting one against varied common forms of dementia, including Alzheimer's disease in which proteins called amyloid clump up and form toxic 'plaques'.

Dementia is a neurodegenerative disorder in which memory, speech and thought processes are steadily affected with age, and can eventually disrupt daily activities.

The study, published in the journal Alzheimer's and Dementia: The Journal of the Alzheimer's Association, looked at whether a disorder of the brain's small blood vessels -- which affects blood flow and can cause vascular dementia -- and cardiovascular risk factors such as blood pressure can damage the glymphatic system and increase risk of dementia.

Analysing MRI brain scans of 40,000 adults in the UK Biobank, the researchers found three biomarkers that may help predict one's risk of dementia over a period of 10 years.

The biomarkers include noting how water spreads along the tiny channels around blood vessels known as perivascular spaces and velocity of the cerebrospinal fluid while flowing into the brain.

"Although we have to be cautious about indirect markers, our work provides good evidence in a very large cohort that disruption of the glymphatic system plays a role in dementia. This is exciting because it allows to ask: how can we improve this?" author Yutong Chen, from the University of Cambridge's department of clinical neurosciences, said.

The authors wrote, "Impaired (cerebrospinal fluid) dynamics may lead to dementia and partially mediate cardiovascular risk-dementia associations."  They added that while cardiovascular risk factors are thought to contribute to dementia through an impacted flow of the cerebrospinal fluid, evidence from humans is low.

The researchers also found that cardiovascular risk factors such as blood pressure and diabetes affected the functioning of the glymphatic system, thereby increasing dementia risk -- in part by causing cerebral small vessel disease.

"We already have evidence that small vessel disease in the brain accelerates diseases like Alzheimer's, and now we have a likely explanation why. Disruption to the glymphatic system is likely to impair our ability to clear the brain of the amyloid and tau that causes Alzheimer's disease," first author Hui Hong, a radiologist at the Second Affiliated Hospital of Zhejiang University in China, said.

The team suggested that good sleep -- important for the functioning of the glymphatic system -- could be a strategy for reducing dementia risk.

There may be existing medicines that could be repurposed, or new ones that could be developed, to improve glymphatic function, they added.