Alzheimer’s disease is the most common cause of dementia, a progressive neurological disease that affects memory, thinking, decision-making, language, and speech, among other brain functions.
The brains of people with Alzheimer’s disease feature two types of abnormal, insoluble protein structures: clumps called amyloid plaques that build up outside brain cells, and tangles of tau protein that build up inside brain cells.
The buildup of these two types of abnormal structure causes brain tissue to degenerate and die, and it also correlates with the progression of behavioral symptoms of the disease.
There is also mounting evidence to suggest that amyloid beta and tau, the two soluble proteins behind plaques and tangles, also “work together, independently of their accumulation into plaques and tangles, to drive healthy neurons into the diseased state.”
The need to investigate sleep quality
Around a third of adults report that they usually get less sleep than the amount recommended.
Not getting enough sleep is a recognized threat to public health. It not only raises the risk of road crashes and mistakes at work that can lead to injury, but it is also tied to higher risk of a number of chronic diseases such as heart disease, diabetes, obesity, and depression.
In their study paper, Prof. Ju and colleagues highlight research in humans and mice that has linked sleep disruption and sleep deprivation to Alzheimer’s disease, as well as to amyloid beta and tau.
For example, people with apnea – a sleep disorder that causes repeated cessation of airflow at night – have a higher risk of developing mild cognitive impairment (MCI) some 10 years earlier than people without apnea.
People with MCI show a slight but measurable decline in memory, thinking, and other mental skills and are more likely to develop Alzheimer’s disease.
But the team notes that, despite the extent of the research, none has yet investigated which aspect of sleep might be responsible.
They make a case for investigating slow wave activity (SWA), a type of deep sleep that differs from rapid eye movement (REM) and that helps us to wake up feeling refreshed and rested. They describe SWA as a “strong candidate” for influencing levels of amyloid beta.
SWA sleep is thought to be a resting time, wherein the brain clears away molecular waste products that build up in brain cells during the day, when they are active.