Levels of A-beta rose in a volunteer’s brain after sleep deprivation, shown by the arrow.
Alzheimer’s, the most common form of dementia, affects millions of people every year. In India, more than 4 million people suffer from some form of dementia, out of the total 44 million people globally. More and more studies are pointing to a link between sleep and Alzheimer’s — lack of sleep may increase the risk of the disease.
Amyloid beta is a protein that is generated as waste by neurons. Higher levels of A-beta are found in people suffering from Alzheimer’s. The body generally cleans up this protein, but this cleaning up process seems to be occurring during sleep. Thus, lack of sleep means inefficient cleaning up of A-beta, which eventually could lead to its accumulation in the brain’s pathways, causing Alzheimer’s.
A study of more than 1500 people at University of Wisconsin-Madison being carried out since 2001 had some interesting results which also point to similar possibilities.
A subgroup of 98 people in this study recorded their sleep quality. Of these, those who reported having slept poorly also had high levels of A-beta. In a different group of 101 people, analysis of spinal fluid was carried out. Here as well, people who had insufficient sleep showed A-beta plaques as well as tau protein and inflammation — again indicators of Alzheimer’s.
However, Alzheimer’s is a well-known cause of sleep problems. The question then becomes, does Alzheimer’s cause sleeplessness, or sleeplessness Alzheimer’s?
While many lab studies on mice give more conclusive results on the relationship between sleep and cognitive problems, there is not sufficient data available for humans.
In mice, researchers have also shown the opposite correlation to exist — the mice which had higher presence of A-beta plaques had disruptions when sleeping for longer durations.
But for humans, it is difficult to conclusively say anything as the brain developments leading to Alzheimer’s occur over many decades. Study subjects will be willing to be give up sleep for a few days for making observations about developments in the brain, but it is not possible to deprive anyone of sleep for years to carry out research.
There have also been studies which show inconsistencies in these conclusions.
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In a study published in Sleep, researchers measured A-beta levels in a group of 13 volunteers. The measurements were done for the first time after five days of good sleep, following which the participants were asked to cut back to four hours of sleep for five nights. Four of the volunteers went for eight days on four hours of sleep. However, A-beta levels did not show much difference, again pointing to a need for more research over longer stretches of time.
The cleaning up of A-beta and other metabolical waste takes place when cerebrospinal fluid circulates in the brain, washing away wastes in the process. Both in mice and in humans, different studies have shown better circulation of the fluid in the well-rested specimens.
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Considering the high number of people affected by Alzheimer’s, it is important to determine if something as simple as good quality sleep could decrease the chances of, or prevent, being afflicted with the disease.
Barbara Bendlin, one of the researchers at University of Wisconsin-Madison, says, “If we find out that sleep problems contribute to brain amyloid — what that really says is there may be a window to intervene.”