Study suggests these are potentially modifiable risk factors

Vision and hearing impairment among older adults are associated with an increased risk of dementia and are potentially modifiable risk factors, according to a cohort study of adults over the age of 65.

The study showed that dual sensory impairment is prevalent in older adults (about 15% of adults over the age of 90) and that it is associated with a higher 7-year risk of dementia compared with no sensory impairment.

Without effective prevention and new treatment, the number of older U.S. adults with dementia is projected to more than double to 13.8 million by 2015. Thus, “reducing dementia risk through identification of and intervention on potentially modifiable risk factors is a public health priority,” wrote from Pei-Lun Kuo, MD, MPH, PhD, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and colleagues in JAMA Network Open,

And, while studies have shown that sensory impairment may put older individuals at greater risk for dementia, Kuo and colleagues pointed out that studies looking at sensory loss and dementia have focused on vision and hearing impairment in isolation. However, the authors pointed out that it is quite common for older adults to experience both hearing and vision impairment at the same time, and that these persons may be at a particularly high risk for dementia.

In this study, Kuo and colleagues used data from the National Health and Aging Trends study, a nationally representative study of Medicare beneficiaries, to examine both the prevalence of dual sensory impairment in older adults and the association between functional dual sensory impairment and dementia.

As defined for purposes of the study, participants were considered to have functional vision impairment if they reported having blindness, an inability to see well enough to recognize someone across the street, or inability to see well enough to read newspaper print. They were considered to have functional hearing impairment if they reported deafness, hearing aid use, inability to hear well enough to use the telephone, or inability to hear well enough to carry on conversation in a room with the television or radio playing.

The authors found that of the 7,562 study participants, 5.4% reported having just functional vision impairment, 18.9% reported having functional hearing impairment only, and 3.1% reported having functional dual sensory impairment. Almost three-quarters of study participants (72.6%) reported having no impairments.

Participants reporting functional visual, hearing, or dual sensory impairment also had a greater burden of disease compared to those with no impairment, with higher rates of diabetes (32.9% dual sensory impairment versus 22.43% no impairment), hypertension (71.27% versus 62.98%,), stroke (19.91%, versus 8.11%), heart attack (19.91% versus 8.11%), heart disease (25.49% versus 15.30%), and lung disease (18.74% versus 14.30%).

In addition, the prevalence of functional sensory impairments increased with older age, particularly once individuals reached the age of 90. For example, the prevalence of functional dual sensory impairment was just 1.4% among individuals age 65 to 69 years but was 14.9% among those 90 years or older.

Finally, functional vision, hearing, and dual sensory impairment were all associated with a higher 7-year risk of dementia compared with no sensory impairment.

What explains this association between functional sensory impairment and dementia? Kuo and colleagues wrote that there could be several explanations. For example, they suggested that sensory impairments may causally increase dementia risk through changes in brain structure and function, and that sensory impairment can lead to depression, social isolation, and less physical activity, all of which are known to be associate with increased dementia risk.

“Additional research is needed to test hypotheses regarding potential mechanisms,” they wrote, adding that further research is also needed to identify prevention strategies to reduce dementia risk associated with sensory impairment.

In a commentary accompanying the study, Elham Mahmoudi, PhD, MS, University of Michigan, Ann Arbor, wrote that while it confirms previous research showing a link between sensory impairment and dementia, “an adjunctive to this study would require accounting for selection bias in clinical comorbidities, which should be examined further in subsequent work.”

Mahmoudi added that the key to timing potential interventions may lie with identifying the age thresholds at which targeted clinical care could reduce or delay the onset of dementia. For example, Mahmoudi noted that while treating hearing, vision, or dual sensory improvement can improve quality of life, it isn’t clear whether such treatment after a certain age reduces the risk of dementia.

“Additional research targeting different age groups is needed to assess treatment efficacy of modifiable factors on dementia risk,” Mahmoudi suggested.

The study authors noted several limitations of their research — dementia was not clinically assessed; functional sensory impairment was self-assessed by the participants and may have been under/over reported; the patients reports of functional sensory impairments could have been affected by their cognitive status; conservative bias may have been due to drop out rate of participants with sensory impairment and at risk for dementia; and individuals in nursing homes or other residential facilities were not included in the analysis.

  1. Functional dual sensory impairment in older adults was associated with a higher 7-year risk of dementia compared with no sensory impairment.

  2. Hearing and vision loss are potentially modifiable risk factors in this population.

Michael Bassett, Contributing Writer, BreakingMED™

None of the authors cited in this article declared any relevant relationships.

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