Aging is a global phenomenon, occurring throughout the body, which is why correlations between the pace of different manifestations of degenerative aging are likely to happen and not necessarily linked by anything other than the fundamental causes of aging:
[Researchers] studied 1,984 older adults (average age about 77 years) enrolled in a prospective observational study that began in 1997-1998. A total of 1,162 individuals with baseline hearing loss had annual rates of decline in test scores that measured global and executive function that were 41 percent and 32 percent greater, respectively, than those among individuals with normal hearing. Compared to those individuals with normal hearing, individuals with hearing loss at baseline had a 24 percent increased risk for incident cognitive impairment, according to the study results.
"Our results demonstrate that hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults," the authors comment. "The magnitude of these associations is clinically significant, with individuals having hearing loss demonstrating a 30 percent to 40 percent accelerated rate of cognitive decline and a 24 percent increased risk for incident cognitive impairment during a six-year period compared with individuals having normal hearing."
The authors suggest that, on average, individuals with hearing loss would require 7.7 years to decline by five points on the 3MS (the Modified Mini-Mental State Examination, a commonly accepted level of change indicative of cognitive impairment) compared with 10.9 years in individuals with normal hearing.