Olfactory function and neurocognitive outcomes in old age: The Atherosclerosis Risk in Communities Neurocognitive Study.

INTRODUCTION: We tested the hypothesis that poor sense of smell is associated with lower cognitive function and higher mild cognitive impairment (MCI) prevalence.

METHODS: Olfaction, measured by the Sniffin' Sticks test, was categorized as olfactory impairment (OI) (score ≤6) or no OI (score >6). MCI was adjudicated based on review of a neuropsychological examination. Linear regression estimated the mean difference in cognitive factor scores, and log-binomial regression quantified MCI prevalence among participants with versus without OI.

RESULTS: Participants with OI had lower mean factor scores (memory: -0.27 standard deviation [SD], 95% confidence interval [CI]: -0.35 to -0.19; language: -0.24 SD, 95% CI: -0.30 to -0.17; executive function/processing speed: -0.09 SD, 95% CI: -0.12 to -0.06; and general cognitive performance: -0.25 SD, 95% CI: -0.30 to -0.20). OI was also associated with MCI (n = 204; prevalence ratio = 1.56, 95% CI: 1.37, 1.78).

DISCUSSION: An impaired sense of smell may serve as a readily accessible early marker of neurodegeneration and improve upon the prevailing delayed diagnoses and underascertainment of MCI/dementia.