The World Health Organization (WHO) has identified dementia as a public health priority that requires more research, especially into causes and modifiable risk factors.  Today, there are around 50 million people living with dementia worldwide, and this figure is set to rise to 75 million by 2030.  There are currently no effective treatments that prevent or reverse the course of the disease.

Recent research adds to a growing body of knowledge that links hearing loss with brain (cognitive) decline.  Cognitive decline is a hallmark of dementia and often precedes the disease.

Research suggests a link between hearing loss and cognitive decline.

How the study was done

The researchers analyzed 8 years of data from a health study of more than 10,000 men to see if they could find a link between hearing loss and subjective cognitive decline.  Subjective cognitive decline refers to changes in memory and thinking that people notice in themselves. Such changes can be an early indication of cognitive decline that medically administered tests do not pick up on.  

The 10,000 men can from a study called the Health Professionals Follow-Up Study (HPFS).  The HPFS recruited 51,529 men who worked in the health professions and who were aged between 40 and 75 years when the study began in 1986. Their professions ranged from podiatry and dentistry to veterinary medicine and optometry.  Following enrollment, the men completed questionnaires about lifestyle, medication use, diet, and medical history every 2 years.

In 2006, over 28,000 of the men responded to a question about their hearing. Of these, nearly 26,000 completed regular six-item questionnaires that included items about subjective cognitive function.  From this group, the researchers extracted data on just over 10,000 men who met the criteria for their analysis. They left out, for example, men who did not complete all the follow-up questionnaires on subjective cognitive function.  They also excluded men with severe diseases such as Parkinson’s or stroke, as either the condition or the medication could influence the results.  The team defined subjective cognitive decline as the appearance, during the follow-up, of at least one new concern.

When they analyzed the data, the researchers found that, compared with men who reported no hearing loss in 2006:

• Those who reported mild hearing loss had a 30 percent higher risk of subsequent subjective cognitive decline.
• Those who reported moderate hearing loss had a 42 percent higher risk.
• Those who reported severe hearing loss — but who were not using hearing aids — had a 54 percent higher risk.

In addition, the analysis revealed that participants with severe hearing loss who did use hearing aids had a lower, 37 percent, risk of subsequent subjective cognitive decline.  However, the authors point out that this result was not statistically significant – that is from this study the authors could not tell if hearing aids could reduce the risk of dementia.

Hearing loss and cognitive decline

In the United States, a national survey has estimated that around 23 percent of those aged 12 or older have some level of hearing loss.  The majority of individuals affected have mild hearing loss. However, in those aged 80 or older, moderate loss is more common than mild loss.

The authors point out that from this study on its own there is not enough evidence to say that hearing loss can cause cognitive decline.  This study does identifies hearing loss as an early stage risk factor for cognitive decline and dementia.  So, while this study does not provide immediate insight into the treatment or prevention of dementia, early diagnosis can do much to improve the quality of life for people with dementia and those who care for them.

With more research, however, identifying early decline in memory and thinking capacity could help develop treatments that are more effective than our current treatments which can be used only in later stages (after signs of cognitive loss are apparent) of dementia.  The researchers plan to conduct further studies of the relationship between hearing loss and brain function in different populations such as women and younger men.