A new study suggests that there may be profound connections between hearing impairment and the risk of developing dementia, the degenerative condition which is characterized by a progressive deterioration of cognitive function and the ability to process thought intelligently.

The researchers found the risk of cognitive decline was nearly double in older people with mild hearing loss and it quintupled in those exhibiting severe hearing impairment compared with those with normal hearing.

Lead author of the study, Dr. Luigi Ferrucci, chief of the U.S. National Institute on Aging's Longitudinal Studies Section, as well as director of the Baltimore Longitudinal Study of Aging, stated, "This work suggests that there is a strong predictive association between hearing loss as an adult and the likelihood of developing cognitive decline with aging."

Link between hearing loss and dementia assessed
In a bid to determine if hearing loss could be identified as a risk factor for dementia, the researchers conducted a study.

They focused on 639 adults aged 36 to 90 who were without dementia at the onset of the study in 1990.

All the study subjects underwent cognitive and hearing testing over a period of 4 years. They were then monitored for the development of dementia and Alzheimer's through May 31, 2008.

It was noted that 125 had mild hearing loss (25 to 40 decibels), 53 had moderate hearing loss (41 to 70 decibels) while six exhibited severe hearing loss (more than 70 decibels).

Revelations of the study
A follow-up at 11.9 years found 58 participants were diagnosed with dementia, including 37 who had Alzheimer's disease.

It was noticed that the risk of dementia elevated in those with hearing loss of greater than 25 decibels.

After taking into account age and other risk factors, the investigators found that the danger of cognitive decline was two fold higher in those with mild hearing impairment.

Additionally, the risk of being diagnosed with dementia was three times higher in those with moderate hearing loss which rose five-fold for severe impairment compared with normal hearing.

Dr Lin stated, "Hearing loss may be causally related to dementia, possibly through exhaustion of cognitive reserve, social isolation, environmental deafferentation [elimination of sensory nerve fibres or a combination of these pathways.

"If confirmed in other independent cohorts, the findings of our study could have substantial implications for individuals and public health."

The research was published in the 'Archives of Neurology.'