Researchers at the University of Oxford found evidence that elderly people showing difficulty hearing spoken conversations in relatively noisy environments, such as a bustling street or pub, may face an up to 91% increased risk of dementia later in life.

According to the World Health Organization (WHO), up to 1.5 billion individuals suffer from some form of hearing impairment. Approximately 30 percent of adults aged 65 and older, and 55 percent older than 80 years show some degree of hearing loss. Besides affecting their quality of life, this disability may also contribute to the risk of dementia.

In a 2015 study, researchers at Johns Hopkins found that mild hearing loss doubled dementia risk and moderate loss tripled the risk. People with a severe hearing impairment were five times more likely to develop dementia.

“Brain scans show us that hearing loss may contribute to a faster rate of atrophy in the brain,” said Frank Lin, the director of the Cochlear Center for Hearing and Public Health at Johns Hopkins . “Hearing loss also contributes to social isolation. You may not want to be with people as much, and when you are you may not engage in conversation as much. These factors may contribute to dementia.”

Although the exact association between hearing loss and dementia is unclear, emerging research suggests that poor hearing may impact memory care drastically in the coming years.

A hallmark of hearing impairment is difficulty understanding speech in noisy environments, which scientists refer to as speech-in-noise hearing impairment. However, up until very recently, it was unclear if this particular facet of hearing impairment was associated with developing dementia. Turns out it is, according to researchers at the University of Oxford’s Nuffield Department of Population Health.

“Difficulty hearing speech in background noise is one of the most common problems for people with age-related hearing impairment. This is the first study to investigate its association with dementia in a large population,” said Dr. Jonathan Stevenson, lead author of the new study.

Stevenson and colleagues surveyed 82,000 men and women aged 60 years or older who enrolled in the UK Biobank program. The participants had to identify certain spoken words against a background of white noise. Based on their scores, they were divided into three distinct groups: normal, insufficient, and poor speech-in-noise hearing.

Over 11 years of follow-up, 1,285 participants developed or were in the course of developing dementia. When the researchers modeled their hearing loss scores and adjusted for other factors, they were stunned to find insufficient and poor speech-in-noise hearing were associated with a 61% and 91% increased risk of developing dementia, compared to normal speech-in-noise hearing, respectively.

In order to explain how hearing impairment may lead to dementia, some have suggested that hearing impairment could lead to social isolation and depression, and it is these factors that actually later contribute to dementia. However, this new research found no such evidence.

“While most people think of memory problems when we hear the word dementia, this is far from the whole story. Many people with dementia will experience difficultly following speech in a noisy environment – a symptom sometimes called the ‘cocktail party problem’. This study suggests that these hearing changes may not just be a symptom of dementia, but a risk factor that could potentially be treated,” Dr. Katy Stubbs from Alzheimer’s Research UK said in a statement.

The good news is that speech-in-noise hearing impairment is very easy to diagnose, so it could provide people with an early warning sign that dementia may be looming. Although there is no cure for dementia, it can be postponed and managed as long as precautions are taken years in advance.

“Dementia affects millions of individuals worldwide, with the number of cases projected to treble in the next few decades. However, there is growing evidence that developing dementia is not inevitable and that the risk could be reduced by treating pre-existing conditions. Whilst preliminary, these results suggest speech-in-noise hearing impairment could represent a promising target for dementia prevention,” said Dr. Thomas Littlejohns, senior epidemiologist in the Nuffield Department of Population Health(NDPH), and senior author of the study.

The findings appeared in the journal Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association..