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Hearing loss predicted increased cognitive decline in older adults, according to results of two studies.

In an observational study, baseline hearing loss was associated with 30% to 40% greater cognitive decline per year as compared with similar patients without hearing loss. The difference translated into a 24% increased risk of cognitive decline in the hearing impaired group during 6 years of follow-up, reported Frank Lin, MD, PhD, of Johns Hopkins Center on Aging and Health, and colleagues in JAMA Internal Medicine online.

"On average, individuals with hearing loss would require 7.7 years to decline by five points on the Modified Mini-Mental State Examination (3MS) ... versus 10.9 years in individuals with normal hearing," the authors wrote.

"Further studies are needed to investigate what the mechanistic basis of this association is and whether hearing rehabilitative interventions could affect cognitive decline," they added.

A related research letter in JAMA Internal Medicine by Bonnielin Swenor, MPH, of the Wilmer Eye Institute at Johns Hopkins, and colleagues showed that one in nine persons, ages 80 and up, has concomitant hearing and vision loss, a rate substantially higher compared with previous studies based on patient self-reporting.

About two-thirds of adults age 70 and older have hearing loss. Some studies have suggested an association between hearing loss and decline in cognitive function and dementia. However, the results have been inconsistent, possibly reflecting differences in study populations and in the methods used to assess hearing and cognitive function.

A definitive link between hearing loss and accelerated cognitive decline would constitute a first step toward evaluation of interventions that might prevent the decline or slow the rate of decline.

Seeking to clarify the relationship between hearing loss and declining cognitive function, Lin and colleagues prospectively assessed 1,984 participants in a longitudinal health study. The participants had a mean age of 77.4 and were followed for 6 years.

The assessment consisted of the 3MS (global functioning), Digit Symbol Substitution (DSS) test (executive function), and standard audiometric hearing evaluation. Cognitive impairment was defined as a 3MS score <80 or a five-point decline from baseline.

At baseline, 1,162 study participants had hearing loss, defined as pure-tone average >25 dB. During follow-up, participants with baseline hearing loss had 42% greater annual decline in the 3MS score and a 32% greater annual decline in the DSS compared with participants with normal hearing.

The annual rate of decline in the 3MS was -0.65 versus -0.46 for the hearing impaired versus nonimpaired groups (P=0.004). Annual rates of change on the DSS were -0.83 versus -0.63 (P=0.02).

Compared with the normal-hearing group, participants with baseline hearing loss had hazard ratio of 1.24 for incident cognitive impairment.

"Rates of cognitive decline and the risk for incidence cognitive impairment were linearly associated with the severity of an individual's baseline hearing loss," the authors noted.

The second study of concomitant hearing loss and vision impairment involved participants in the National Health and Nutrition Examination Survey (NHANES) from 1999 through 2006.

As part of the NHANES health assessment, all participants, ages 20 to 69, underwent pure-tone audiometric evaluation of hearing from 1999 through 2004 as did all participants ages 70 and up during 2005 and 2006. Hearing loss was defined as pure-tone average >25 dB.

All participants ≥20 had assessment of visual acuity from 1999 through 2006. Vision impairment was defined as postautorefraction visual acuity worse than 20/40 in the eye with better vision.

The data showed that no participant in the age range of 20 to 39 had concomitant hearing and vision impairment. Participants 40 to 49 and 50 to 59 had a prevalence of 0.1%, increasing to 0.3% in the 60 to 69 age group, 2.2% in participants 70 to 79, and 11.3% of participants ≥80.

Hearing impairment became increasing prevalent with age:

• 40 to 49: 5.7% of participants
• 50 to 59: 13.7% of participants
• 60 to 69: 29.3% of participants
• 70 to 79: 55.1% of participants
• ≥80: 79.1% of participants

Prevalence of vision impairment increased from <1% up to age 59 to 1.1% in the 60 to 69 group, 3.4% of the 70 to 79 group, and 15.9% of participants ≥80.

The proportion of participants without impaired hearing or vision declined in each age group:

• 20 to 29: 99% of participants
• 30 to 39: 97.4% of participants
• 40 to 49: 94.2% of participants
• 50 to 59: 86.3% of participants
• 60 to 69: 69.8% of participants
• 70 to 79: 44.1% of participants
• ≥80: 18.8% of participants

In an editor's comment, Patrick G. O'Malley, MD, said the two studies did not provide sufficient evidence to mandate screening for both types of impairment. However, physicians should be alert to signs of impairment, given that effective treatment exists for hearing and vision loss.

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