Auditory threshold, phonologic demand, and incident dementia.
Gallacher J., Ilubaera V., Ben-Shlomo Y., Bayer A., Fish M., Babisch W., Elwood P.
OBJECTIVE: This study was undertaken to investigate the association of auditory threshold with cognitive decline and dementia. METHODS: The 1,057 surviving men of the Caerphilly cohort with audiometric data at baseline were followed for 17 years for cognitive outcomes. Pure-tone unaided audiometric threshold was assessed at 0.5, 1, 2, and 4 KHz at baseline and after 9 years. Incident dementia was assessed according to DSM-IV criteria, including standard criteria for vascular dementia and for Alzheimer disease. Cognitive decline was assessed by repeat administration of a cognitive test battery. RESULTS: Mean age-adjusted auditory threshold across both time points was associated with incident dementia and cognitive decline. After adjustment for premorbid cognitive function, the association with dementia was retained (odds ratio(0.5 KHz) = 2.67; 95% confidence interval, 1.38-5.18; p = 0.004). Stronger associations with cognitive decline were found for tests administered by interview than for those administered by computer. CONCLUSIONS: This study has found an association of auditory threshold with dementia and cognitive decline over a 17-year period. The mechanisms underlying this association are unclear and may include a prodromal effect of dementia on auditory threshold, an effect of auditory threshold on cognitive assessment, an effect of auditory threshold on cognitive loss, or a shared etiologic pathway between both.