ASSOCIATION BETWEEN OLFACTORY IDENTIFICATION ABILITY AND COGNITIVE FUNCTION IN NON-DEMENTED ELDERLY

Abstract

Olfactory function declines gradually as aging and is impaired in people with neurodegenerative disorder. The deficit of odor identification has been used to predict mild cognitive impairment (MCI), Alzheimer's disease (AD), and conversion from MCI to AD. However, limited studies have related olfactory function to cognitive domains in community-dwelling elders. This cross-sectional study (2015-2017) is part of a cohort study “Taiwan Initiative for Geriatric Epidemiological Research”, and 605 community-dwelling elders (aged 65+) were recruited from elderly health checkup program at National Taiwan University Hospital between 2011 and 2013. The target population included 415 elders who completed the 4-year follow-up and without cognitive impairment. The cross-culture modified version of 15-item Sniffin’ Sticks Odor Identification Test (SS-OIT) was used to evaluate the ability of identifying odorants. The Montreal Cognitive Assessment-Taiwanese version (MoCA-T) and a battery of neuropsychological tests were administered to assess the global and domain-specific (logical memory, executive function, verbal fluency, and attention) cognition. Multivariable linear and logistic regression models were utilized to assess the association between the olfactory identification ability and cognitive function adjusting for important covariates (e.g., age, sex, years of education, apolipoprotein E ε4 carrier, and instrumental activities of daily living). Better olfactory identification ability (i.e., increased SS-OIT score) was associated with better performance of global cognition [β=0.22, 95% confidence interval (CI)=0.1−0.35; T3 vs. T1+T2: adjusted odds ratio (aOR)=3.93, 95% CI=1.29-11.95], logical memory (β=0.07, 95% CI=0.03−0.1; T3 vs. T1+T2: aOR=1.69, 95% CI=1.03-2.79), verbal fluency (β=0.07, 95% CI=0.04−0.1; aOR=2.4, 95% CI=1.43-4.02), and attention (aOR=1.96, 95% CI=1.13-3.41). After stratified analyses, the associations above remain significant in men (logical memory, aOR=3.6; verbal fluency, aOR=3.26), the older population (age ≥ 75, logical memory, aOR=2.69; verbal fluency, aOR=2.24; attention, aOR=2.36), elders with lower daytime sleepiness (verbal fluency, aOR=1.96; attention, aOR=2.04), and those with less functional decline (logical memory, aOR=1.71; verbal fluency, aOR=2.19; attention, aOR=2.34). Our results revealed a positive association of odor identification with global and domain-specific (logical memory, verbal fluency, and attention) cognition in non-demented elders. These findings provide more understanding of olfactory identification in relation to cognitive domains to identify AD in the pre-clinical phase.