People who struggle to hear their companions chattering in a bustling restaurant are in good company. Difficulty hearing speech when there's background noise is a common problem for those with age-related hearing loss. And, while there's a plethora of studies that assess whether hearing loss is linked to dementia, not a single reliable one specifically assesses the link to "speech-in-noise" impairment.
A new study has now filled that gap.
The Lancet Commission recently identified 12 risk factors that might prevent or delay up to 40 percent of dementias. (The Lancet Commission, is a group of editors from the medical journal The Lancet who work with academic partners to identify pressing issues in medicine with the aim of providing recommendations that change health policy or improve health practice.)
After their research, the commission suggested hearing loss could be responsible for eight percent of all dementia cases. While this figure may sound low, it’s the highest of the risk factors apart from education, and potentially the most modifiable if every person with hearing impairment wore a hearing aid.
How to Assess Hearing and Memory Loss
Hearing is usually assessed in studies by measuring sensitivity to a pure tone in a quiet environment. But reduced sensitivity is only one way in which hearing becomes impaired. People also struggle to hear in a noisy environment.
Only two studies have ever examined this aspect of hearing impairment and while they did find a link to dementia, the studies were small and the findings unreliable.
This encouraged researchers at Nuffield Department of Population Health, University of Oxford, to carry out a study of their own.
What they found is alarming…
Poor Hearing Almost Doubles Dementia Risk
The Oxford researchers analyzed data from 82,039 participants in the United Kingdom Biobank research project. All the men and women were age 60 or over and free from dementia when the study began.
Over the next four years each participant undertook speech-in-noise (SIN) hearing tests which are designed to reflect real world experience. Each participant’s hearing was then rated as normal, insufficient, or poor.
After eleven years of follow up, 1,285 of the participants developed dementia. The key finding was then compared to normal SIN hearing, those in the insufficient hearing category had a 61 percent increased risk of dementia. For those with poor hearing this risk rose to a whopping 91 percent.
Those numbers are shocking. But this was only the beginning of the research.
Some experts theorize that hearing loss itself is not a cause of dementia. Instead, it can lead to social isolation and depression. These are the true culprits. Interestingly, the researchers tested this theory and found little evidence to support it.
They also tested reverse causation. Since the beginnings of brain pathology seen in dementia occur over many years, possibly decades, before symptoms of cognitive decline appear, this could be the driver of hearing impairment and not the other way around. However, they found no evidence to support this either.
A Promising Target for Dementia Prevention
The overall findings of this study add weight to the theory that hearing problems are a genuine risk factor for dementia and not a symptom of the disease.
What’s more, the researchers say this study is good news.
Dr. Thomas Littlejohns, senior author of the study, said, "Whilst preliminary, these results suggest speech-in-noise hearing impairment could represent a promising target for dementia prevention."
Dr. Katy Stubbs from Alzheimer's Research United Kingdom agreed, saying, "Many people with dementia will experience difficulty following speech in a noisy environment - a symptom sometimes called the 'cocktail party problem' [or effect]. This study suggests that these hearing changes may not just be a symptom of dementia, but a risk factor that could potentially be treated."
By the way, for the last decade, I’ve had a problem with understanding what people are saying in noisy environments. However, my hearing is actually above average for someone my age. Still, if you have this symptom it’s a good idea to have a medical examination.