BALTIMORE–A study that followed nearly 2000 older Americans for more than a decade found that those with hearing loss had 30%-40% greater annual declines on measures of cognitive function than did those whose hearing was normal.
Senior author Frank R. Lin, MD, an assistant professor at the Johns Hopkins University School of Medicine, and nine other scientists reported their findings in the January 21 web edition of JAMA Internal Medicine. According to their article, the study, which was funded by the National Institutes of Health, reached the following conclusions: “Hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults. Further studies are needed to investigate what the mechanistic basis of this association is and whether hearing rehabilitative interventions could affect cognitive decline.”
The 1984 people studied by Lin et al. were drawn from the Health, Aging and Body Composition (ABC) Study Group, a prospective observational study begun in 1997-1998 to monitor the health of older people in Pittsburgh, PA, and Memphis, TN.
When the study began in 2001, the members of the ABC Study Group who volunteered to participate had a mean age of 77.4 years and had normal brain function. In year five of the study, all participants underwent audiometric testing to determine their baseline hearing.
Based on the subjects’ pure-tone average thresholds from 500 to 4000 Hz in the better ear, researchers determined that 1162 of the subjects had hearing loss. This was defined as being unable to hear sounds until they were more than 25 dB louder than those audible to people with normal hearing.
Cognitive testing was performed on all participants in years 5, 8, 10, and 11. Two tests were used: the 3MS, which measures global function, and the Digit Symbol Substitution test, which measures executive function.
Those with hearing loss had annual rates of decline on the 3MS test 41% greater than those of the normal-hearing participants. On the Digit Symbol Substitution Test, their scores declined at a 32% faster annual rate. Compared to those with normal hearing, individuals with hearing loss at baseline had a 24% increased risk for incident cognitive impairment.
Rates of cognitive decline and the risk for incident cognitive impairment were linearly associated with the severity of an individual’s baseline hearing loss.
In an interview (“Hearing loss may be related to cognitive decline”) with the press office of Johns Hopkins Medicine, Lin, an otologist, discussed the significance of his group’s findings: “Our results show that hearing loss should not be considered an inconsequential part of aging, because it may come with some serious long-term consequences to healthy brain functioning.”
He added, “Our findings emphasize just how important it is for physicians to discuss hearing with their patients and to be proactive in addressing any hearing declines over time.”
While the study did not try to explain why hearing loss might lead to cognitive decline, Lin noted that social isolation has previously been found to be a risk factor for cognitive problems. Also, he suggested, hearing loss may force the brain to devote extra energy to processing sound at the expense of using it for memory and thinking.