An Epidemiologic Study of the Association between Free Recall Dichotic Digits Test Performance and Vascular Health
Authors: Fischer Mary E. , Cruickshanks Karen J. , Dillard Lauren K. , Nondahl David M. , Klein Barbara E. K. , Klein Ronald , Pankow James S. , Tweed Ted S. , Schubert Carla R. , Dalton Dayna S. , Paulsen Adam J. 
Published: February 2018

Background:Associations between vascular health‐related factors and hearing loss defined using audiometric pure-tone thresholds have been found. Studies have not focused on a potential relationship between vascular health‐related factors and central auditory processing.Purpose:The
aim of this study was to evaluate, on a population level, the relationship of vascular health‐related factors with central auditory function.Research Design:A cross-sectional, population study.Study Sample:Subjects were participants in the Epidemiology of Hearing Loss
Study (EHLS) or the Beaver Dam Offspring Study (BOSS)—prospective studies of aging and sensory loss. BOSS participants were the adult offspring of participants in the EHLS. Participants who completed the Dichotic Digits Test (DDT) during the fourth examination period of the EHLS (2008‐2010)
or the second examination period of the BOSS (2010‐2013) were included (n = 3,655, mean age = 61.1 years).Data Collection and Analysis:The DDT-free recall test was conducted using 25 sets of triple-digit pairs at a 70 dB HL presentation level. The total number of correctly repeated
digits from the right and left ears was converted to a percentage correct and used as an outcome. The percentage correct in the left ear was subtracted from the percentage correct in the right ear and used as an outcome. Vascular health‐related measures obtained during the examination
included blood pressure, mean carotid intima-media thickness, femoral pulse wave velocity (PWV), hemoglobin A1C, and non‐high-density lipoprotein (HDL) cholesterol, and, in the EHLS participants, C-reactive protein and interleukin-6. Information on vascular health‐related history
and behaviors was self-reported. General linear modeling produced estimates of the age- and sex-adjusted least squares means for each vascular factor, and multiple linear regression was used for multivariable modeling of each outcome.Results:After multivariable adjustment, participants
with diabetes had a significantly lower (worse) mean DDT-free recall total score (−2.08 percentage points, p < 0.001) than those without diabetes. Participants who exercised at least once per week had a significantly higher (better) mean DDT-free recall total score (+1.07 percentage
points, p < 0.01) than those who did not exercise at least once per week. Alcohol consumption was associated with a higher DDT-free recall total score (+0.15 percentage points per +25 g ethanol, p < 0.01). In multivariable modeling of the right‐left ear difference
in DDT-free recall scores, participants with a history of cardiovascular disease (CVD) or higher PWV demonstrated significantly larger differences (CVD: +3.11 percentage points, p = 0.02; PWV: +0.36 percentage points per 1 m/sec, p < 0.01). Higher levels of non-HDL cholesterol
were associated with smaller right‐left ear differences (−0.22 percentage points per 10 mg/dL, p = 0.01). Adjustment for handedness did not affect the results.Conclusions:Vascular health‐related factors may play a role in central auditory function.