Introduction Hearing aid usage has been linked to improvements in cognition, communication, and socialization, but the extent to which it can affect the incidence and progression of dementia is unknown. Such research is vital given the high prevalence of dementia and hearing impairment in older adults, and the fact that both conditions often coexist. In this study, we examined for the first time the effect of the use of hearing aids on the conversion from mild cognitive impairment (MCI) to dementia and progression of dementia. Methods We used a large referral‐based cohort of 2114 hearing‐impaired patients obtained from the National Alzheimer's Coordinating Center. Survival analyses using multivariable Cox proportional hazards regression model and weighted Cox regression model with censored data were performed to assess the effect of hearing aid use on the risk of conversion from MCI to dementia and risk of death in hearing‐impaired participants. Disease progression was assessed with Clinical Dementia Rating Sum of Boxes (CDR‐SB) scores. Three types of sensitivity analyses were performed to validate the robustness of the results. Results MCI participants that used hearing aids were at significantly lower risk of developing all‐cause dementia compared to those not using hearing aids (hazard ratio [HR] 0.73, 95% confidence interval [CI], 0.61 to 0.89; false discovery rate [FDR] P = 0.004). The mean annual rate of change (standard deviation) in CDR‐SB scores for hearing aid users with MCI was 1.3 (1.45) points and significantly lower than for individuals not wearing hearing aids with a 1.7 (1.95) point increase in CDR‐SB per year (P = 0.02). No association between hearing aid use and risk of death was observed. Our findings were robust subject to sensitivity analyses. Discussion Among hearing‐impaired adults, hearing aid use was independently associated with reduced dementia risk. The causality between hearing aid use and incident dementia should be further tested.

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Age-related hearing loss (ARHL) is postulated to affect dementia. Our study aims to investigate the relationship between ARHL and the prevalence, and 10-year incidence of dementia in the Taiwan National Health Insurance Research Database (NHIRD). We selected patients diagnosed with ARHL from the NHIRD. A comparison cohort comprising of patients without ARHL was frequency-matched by age, sex, and co-morbidities, and the occurrence of dementia was evaluated in both cohorts. The ARHL cohort consisted of 4108 patients with ARHL and the control cohort consisted of 4013 frequency-matched patients without ARHL. The incidence of dementia [hazard ratio (HR), 1.30; 95% confidence interval (CI 1.14-1.49); P = 0.002] was higher among ARHL patients. Cox models showed that being female (HR, 1.34; 95% CI 1.07-1.68), as well as having co-morbidities, including chronic liver disease and cirrhosis, rheumatoid arthritis, hypertension, diabetes mellitus, stroke, head injury, chronic kidney disease, coronary artery disease, alcohol abuse/dependence, and tobacco abuse/dependence (HR, 1.27; 95% CI 1.11-1.45), were independent risk factors for dementia in ARHL patients. We found ARHL may be one of the early characteristics of dementia, and patients with hearing loss were at a higher risk of subsequent dementia. Clinicians should be more sensitive to dementia symptoms within the first 2 years following ARHL diagnosis. Further clinical studies of the relationship between dementia and ARHL may be necessary.

The immune system, particularly T lymphocytes and cytokines, has been implicated in the progression of brain injury after intracerebral hemorrhage (ICH). Although studies have shown that transplanted neural stem cells (NSCs) protect the central nervous system (CNS) from inflammatory damage, their effects on subpopulations of T lymphocytes and their corresponding cytokines are largely unexplored. Here, rats were subjected to ICH and NSCs were intracerebrally injected at 3 h after ICH. The profiles of subpopulations of T cells in the brain and peripheral blood were analyzed by flow cytometry. We found that regulatory T (Treg) cells in the brain and peripheral blood were increased, but γδT cells (gamma delta T cells) were decreased, along with increased anti-inflammatory cytokines (IL-4, IL-10 and TGF-β) and decreased pro-inflammatory cytokines (IL-6, and IFN-γ), compared to the vehicle-treated control. Our data suggest that transplanted NSCs protect brain injury after ICH via modulation of Treg and γδT cell infiltration and anti- and pro-inflammatory cytokine release.

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