Scientists have discovered problems with the brain's ability to clear toxins, which they suggest could be why poor sleep and high blood pressure increase the risk of dementia.
In a healthy brain, the glymphatic system clears out poisons and waste. It flushes cerebrospinal fluid (CSF) – the clear liquid that cushions the brain – through the brain along tiny channels around blood vessels. This fluid collects toxins and drains them out of the brain, keeping it clean and healthy.
But if this process does not work properly, it could increase the risk of dementia later in life. Reduced sleep and cardiovascular problems affect how well the glymphatic system works, according to a study led by researchers at the University of Cambridge.
First author Hui Hong said: “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.”
Alzheimer’s disease, the most common type of dementia, is linked to the build-up of the proteins amyloid and tau in the brain. In Alzheimer's, amyloid sticks and forms plaques in the brain, eventually causing brain cells to die, while tau tangles inside the brain’s neurons – both leading to the onset of dementia symptoms.
Another common form of dementia is vascular dementia, which is caused by reduced blood flow to the brain and affects about 180,000 people in the UK, according to the NHS.
Researchers wanted to see whether cerebral small vessel disease and other cardiovascular risk factors damage the glymphatic system – and whether this in turn increases the risk of dementia.
The study, published in the journal Alzheimer's & Dementia: The Journal of the Alzheimer's Association, used AI to analyse MRI scans from around 40,000 adults in the UK Biobank.
Analysis revealed several risk factors that predicted dementia, including how well CSF flowed into the brain.
Further analysis showed that several cardiovascular risk factors impaired glymphatic function and, as a result, increased dementia risk. This was partly caused by cerebral small vessel disease, which is visible in the MRI scans.
Researchers suggested several ways of reducing dementia risk. One is to improve sleep.
That is because sleep plays an important role in glymphatic function, and the study authors suggested that disrupted sleep patterns impair the brain's ability to clear toxins and waste.
Another approach is to treat vascular problems, such as high blood pressure, which has been shown to increase the risk of small vessel disease and vascular dementia.
Professor Markus, who leads the stroke research group at the University of Cambridge, said: “At least a quarter of all dementia risk is accounted for by common risk factors like blood pressure and smoking.
“If these impair glymphatic function, then we can intervene. Treating high blood pressure or encouraging people to stop smoking would be an achievable way to help the glymphatic system work better.”
There are currently estimated to be 982,000 people with dementia in the UK, but more than a third of people with the condition do not have a diagnosis.
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