Hearing loss is associated with an increased risk of developing dementia according to a prospective analysis of more than 600 people free of cognitive decline. Of those studied, the risk of all-cause dementia rose 27% for every 10-decibel loss of hearing at the start of the almost 12-year study. The risk of Alzheimer’s disease (AD) rose in a similar fashion, but did not reach statistical significance. The study appears in the February issue of Archives of Neurology.

The findings support the idea that social isolation caused by deafness may be part of the cause of dementia. This may be particularly true as the association to dementia was only seen for deafness above the level at which verbal communication was impaired.

Over a five-year period from 1990 through 1994, 795 participants had both hearing and cognitive testing as part of the Baltimore Longitudinal Study of Aging. Of these, the current study consisted of 639 people, ages 36 to 90, free of confirmed or suspected dementia.

The participant subset was followed until May 31, 2008, for a median of 11.9 years. During this time, researchers found 58 participants to be diagnosed with dementia from all causes, including 37 with AD. Most of the participants (456) had normal hearing at baseline with a mean age around 60, while 125 had mild hearing loss, 53 had moderate hearing loss, and six had severe deafness.

Interestingly, in the 15 years before the study period, those who developed dementia had an average yearly hearing loss that was nearly twice average for those who did not develop dementia.