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AMSTERDAM -- Cognitive decline in older adults with dementia risk factors was slower when they wore hearing aids in a randomized trial.

But no benefit from hearing aids was seen in otherwise similar individuals without risk factors for dementia, the results indicated.

Among at-risk individuals, cognitive decline was reduced by 48% over 3 years of follow-up in those assigned to wear hearing aids relative to a control group given general health advice, according to Frank Lin, MD, PhD, of Johns Hopkins University in Baltimore, and colleagues.

In a different segment of the trial sample comprising healthy older people, though, use of hearing aids did not affect participants' cognitive trajectory.

Results of the trial, called the , were presented here at the Alzheimer's Association International Conference and published simultaneously in .

Numerous studies have linked hearing loss with future dementia risk, but the nature of that association, and particularly whether it was causal, has not been clear. In the Lancet paper, Lin and colleagues explained that several theories have been advanced for how hearing loss might exacerbate cognitive decline: coping with it might increase a person's "cognitive load," alter brain structure, and/or discourage "engagement in social and cognitively stimulating activities."

If there is indeed a causal connection, then hearing loss could therefore be a modifiable factor -- hence the impetus for ACHIEVE.

Lin and colleagues enrolled two different sets of people in the trial, both connected to the long-running . This is an observational study that began in 1987 to follow people from middle age into their senior years. It has operated at four U.S. sites in North Carolina, Mississippi, Minnesota, and Maryland. The two ACHIEVE cohorts were 238 current ARIC participants and another 739 newly recruited (the "de novo" group) from the same four ARIC locations. Both groups were randomized 1:1 to receive hearing aids or a health-education program.

In general, the current ARIC participants would be considered at higher risk for future dementia because baseline factors including cognitive performance, educational attainment, and household income were all lower at baseline, and they had higher rates of illnesses such as hypertension and diabetes. This increased estimated risk was confirmed in ACHIEVE, as ARIC participants assigned to the education control experienced significantly greater cognitive decline during the trial's 3-year follow-up than did control participants in the de novo group.

Cognitive ability was primarily measured with a battery of 10 standard tests, such as delayed word recall, trail making, and animal naming. The investigators took pains to minimize the effects of hearing loss itself on test performance; only two of the tests exclusively involved hearing ability.

Secondary cognitive outcomes included the Mini-Mental State Examination and different subsets of the 10 neurocognitive tests specific to executive function, language skill, and memory. Different types of hearing aids were provided, individualized for participants after audiological testing.

ACHIEVE's primary endpoint was overall cognitive ability in both the ARIC and de novo groups pooled together; in this analysis, no benefit for the hearing aids was found. As noted earlier, no benefit was found either for the de novo group.

It was only in the ARIC group that a difference between the intervention and control groups was seen: a decline of 0.211 points with hearing aids versus 0.402 among controls (P=0.027). The biggest differential was in language ability (-0.116 vs -0.344, P=0.012); numerical advantages for the hearing aids were seen in executive function and memory but they fell just short of statistical significance.

Lin and colleagues noted that, because cognitive declines were much smaller in the de novo group -- there was no change at all in mean memory scores -- it would be difficult to see a benefit from hearing aids. Furthermore, some of these participants decided to start using hearing aids on their own, thus diluting the results.

in The Lancet, two University College London researchers wondered at the magnitude of benefit seen in the ARIC participants, which they called "enormous" and perhaps "spurious."

To confirm the results, wrote Gill Livingston, MBBS, and Sergi Costafreda, MD, PhD, new studies should employ broader outcome measures that take in "mood, independence, social network, and physical activity," as well as "quantity of social contact."

In addition, they urged the ACHIEVE investigators to continue follow-up, especially in the de novo group, to determine whether an advantage for hearing aids becomes apparent with continued long-term use.