Dementia is growing amongst Singapore’s elderly population. A neurodegenerative disease, dementia robs individuals of their ability to recall memories, recognize objects, and coordinate movements and regular bodily functions. In a 2015 study by the Institute of Mental Health1, the prevalence of dementia in Singapore was found to be at 10 per cent in elderly aged 60 and above. The same report estimated that in 2020, there were about 50,000 people in Singapore living with dementia.
According to a 2020 Lancet commission2, hearing loss is one of the top modifiable risk factors for dementia. The report encourages wearing hearing aids for people with hearing loss as a way to prevent dementia.
“It was first reported as early as 19893 that elderly adults with hearing loss were likely to have dementia," Dr. Liu explained.
“Subsequent community longitudinal studies found that those with hearing loss actually had a 30 to 40 percent rate of accelerated cognitive decline. These studies correlate with neuro-imaging studies which found that people with dementia had reduced cortical volumes not only in their hearing auditory cortex but overall brain atrophy,” she added.
Cortical functions refer to one’s motor, sensory, and visual functions. This includes knowing how to speak a language, possessing the ability to recognize objects in space, and the awareness of what is happening in our surroundings. A reduced cortical volume is indicative of a lower ability to perform functions relating to speech and recognition. Coupled with overall brain atrophy or damage due to dementia, the person develops difficulty performing basic hearing tasks.
"In a local 2016 study done by National University of Singapore, 10 percent of elderly with hearing loss were found to have mild dementia."
“Hearing loss has the most impressive degenerative effects on humans,” Dr. Liu said.
“The first mechanism of how it can cause dementia is brain atrophy. When we have hearing loss, the auditory cortex of the brain becomes inactive and causes the ageing brain to shrink more quickly,” she added.
The second mechanism is cognitive overload. When someone is unable to hear, the brain must work harder to understand what people are saying; straining to understand this degraded auditory signal every day. This comes at the expense of other thinking and memory systems.
"If we have normal hearing, we don't need to think too hard about hearing. This is because half of our brain matter listens, and the other half is used to do planning and activate our memory. However, for someone with hearing loss, more efforts and majority of the brain energy are needed to concentrate and to try to listen, resulting in accelerated neuro-atrophy and neuro-degeneration," Dr. Liu explained.
The last mechanism is social isolation.
"Babies learn very fast because they interact with the environment. For people with hearing loss, they tend to be more reserved and are usually afraid to go out because of social embarrassment. Most prefer to stay at home and they don't want much interaction with people or the environment. The less social engagement one has, which is hugely important to remaining intellectually stimulated, the faster the brain declines,” she described.
In other words, hearing loss and dementia are interconnected, creating a vicious cycle where degeneration in one part of the brain speeds up the breakdown of neural networks in the other.
“If there's mild hearing loss which is untreated, the dementia risk is 2-fold. If it is moderate hearing loss, it is 3-fold and in the case of severe hearing loss, the lifetime risk is as high as 5-fold. For every 10 decibels of hearing loss, dementia risk increased by about 20 percent,” she cautioned.
The common measure to lower the chances of hearing loss as you age is to protect your hearing from loud noises. However, some people are more likely to get hearing loss as they age.
An appropriate hearing aid can effectively slow down the rate of hearing loss.
“If it is mild hearing loss, we always suggest the use of hearing aids first. After wearing them for a few years, if it is ineffective, cochlear implant is the next step. It is the most powerful hearing device available to date. Dr. Liu advised.
A cochlear implant has internal and external parts. The external part sits behind the ear and picks up environmental sound with a microphone, converting it into electrical signals before transmitting the signal into the internal part, which is surgically implanted into the cochlea. Stimulation of the cochlea then sends auditory signal to the cochlear nerve and up to the auditory cortex of the brain to produce a hearing sensation.
While some elderly patients may understandably recoil at the thought of surgery, inserting the cochlear implant is actually a minimally invasive procedure.
Dr. Liu shared the experience interacting with her first cochlear implant patient at Farrer Park Hospital. “Before the surgery, I communicated with her by writing on paper. Otherwise, it was just silence in the room. Now she can respond directly to my questions and there is no more writing back and forth with her anymore.”
These implants are designed to last for over 70 years, with more and more of them being built with rechargeable batteries so that patients can continue using them with minimal disruptions to their daily lives.
Even though hearing aids help restore hearing sensation, Dr. Liu noted hearing aid uptake in the elderly is low, with only 7.5% of the Singapore’s elderly population with hearing loss wearing hearing aids. This low uptake is due to fear of stigmatization, lack of accurate information about hearing loss, and concern about cost of hearing aids. “Speak to an ENT doctor who specializes in hearing loss if you would like to understand more about your condition and the options available” advises Dr Liu.
“Hearing loss does not mean that one will definitely get dementia because dementia is multi-factorial and very complex. Dementia risk is reduced by as much as 8% if an elderly person’s hearing loss is treated. This is very significant " Dr. Liu said.
In addition to treating hearing loss, Dr. Liu said the need to enhance cognitive reserve in the elderly such as engaging in activities like playing music, playing mahjong, planning dinner, or making friends remain essential.
“Early detection and active intervention are also encouraged,” she added.
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