an overlooked risk factor for Alzheimer’s disease

Senile deafness is considered more of a nuisance than a serious health problem. It’s time to abandon this idea. Because, among other things, it is the most important preventable risk factor for developing Alzheimer’s disease.

As is known, the consequences of this disease are devastating. Progressive loss of memory and ability to think. which ultimately influences behavior and personalityLife expectancy is reduced and independence is lost. The individual, family, social and economic losses are severe.

As the population ages and life expectancy increases, the impact of Alzheimer’s disease increases. Approximately 10 million cases of the disease are diagnosed worldwide each year, and the number of people affected is estimated to befor example, in Spain it will grow from 1,000,000 in 2025 to 1,700,000 in 2050.

Therefore, every advance in understanding one’s causes This is a step towards a higher quality of life for people suffering from it.. And, ultimately, to his healing.

Accumulation of waste

In Alzheimer’s disease, basic mechanisms fail to stabilize and process certain proteins in brain cells. which are essential building blocks for your survivalWhen these mechanisms fail, the brain accumulates remnants of defective units, a veritable “protein waste.” Since they were observed by the German scientist Alois Alzheimer in the early 20th century, they allowed the disease to be identified.

Debris (tangles of hyperphosphorylated tau protein inside cells and plaques of beta-bamyloid protein around them) damage neural circuits, preventing signal transmissionThis results in memory loss, inability to solve problems, depression, behavioral changes and personality disintegration.

Sum of risks

It is not known why these basic cellular mechanisms fail. The key appears to be the sum of multiple environmental factors acting on genetic predisposition conditions.. But it is not possible to join the links yet.

in the magazine Lancet(A committee of experts periodically analyzes risk factors for dementia). Their latest estimates suggest that genetic factors account for 55% of the risk.The remaining 45% is made up of 14 environmental factors that operate throughout life, and among them, adult deafness occupies a special place.

This is how deafness progresses

Senile deafness begins after 50 years of age. It affects up to 40% of people over 65 years of age. and 80% of people survived into their eighth decade of life.

First, the highest sounds cease to be heard, early stage, at which hearing loss often goes unnoticedAs it progresses, sufferers lose the ability to perceive deeper sounds, which include a significant portion of the sounds of words. This is when the problem begins to show.

At this stage, using hearing aids slows down the process because the receptor cells of the inner ear are especially damaged. They are like microscopic antennas They receive, amplify sound and convert it into electrical signals that are transmitted to the brain. Hearing aids amplify sound where damaged cells cannot.

But eventually, the brain circuits responsible for hearing are also damaged.. Then amplification by hearing aids helps less: auditory signals, even amplified, are not transmitted correctly through damaged cables. Serious communication problems arise, leading to isolation, withdrawal, anxiety and even depression.

We must realize

Despite this, the idea remains that the impact of deafness is relatively small when consistent messages are given in Lancet indicate that its elimination would reduce the number of new cases of dementia by 7-9%These are high values, unknown before the publication of these works.

It is necessary for health professionals and the general public to become aware of the problem. In the prevention and treatment of dementia, senile deafness is still underestimated compared to other risks.For example, recent work shows that amplifying sound with hearing aids attenuates cognitive decline in high-risk adults.

It is therefore necessary prioritize actions to prevent age-related hearing lossFor example, the link between adult deafness and early life noise exposure cannot be ignored. Targeted educational measures are needed.

Vicious circle

But in addition, we must explore the biological mechanisms that interfere with the link between hearing loss and Alzheimer’s diseaseIn this context, our research group examined whether the disease itself accelerates deafness, creating a vicious circle.

To find out, we use animal models that reproduce at the same time, the peculiarities of deafness in aging and neurodegenerative diseases. Thus, we have become convinced that by experimentally inducing manifestations of Alzheimer’s disease, hearing problems appear earlier. This indicates the existence of the vicious circle.

What could be causing this? There are cells in the inner ear that function like an electric battery: they supply the energy needed by the receptor cells, “antennas“, generate and send auditory signals to the brain.

The area of ​​the inner ear where These “battery cells” contain a large number of small blood vessels.. As we age, cells of the body’s “fast” defense system against attacks appear there: inflammation. According to our observations, inflammatory cells will be more numerous and active in mice with signs of Alzheimer’s disease.

As we get older, these defense mechanisms get out of control and eventually damage other cells. with the aggravating factor that Alzheimer’s disease can increase inflammation and increase wear on the inner ear “battery”. This will accelerate the development of deafness, which in turn will worsen the neurodegenerative condition.

Research into the link between hearing loss and Alzheimer’s disease could open up new avenues for improved prevention and treatment.

Jose M. Huis, Professor of Histology/Professor of Histology, University of Castilla-La Mancha

This article was originally published on The Conversation. Read the original.