Association Between Olfactory Dysfunction and Cognitive Impairment in Dementia-Free Older Adults: A Prospective Cohort Study in Taiwan

Abstract

Background: Previous studies assessing olfactory function and cognition have mostly been cross-sectional, and few have investigated the Asian geriatric population. Objective: To examine the relationships of olfaction with global or domain-specific cognitive function in Taiwanese community-dwelling older adults. Methods: This cohort study (2015–2019) is part of the Taiwan Initiative for Geriatric Epidemiological Research. The Taiwanese version of the Montreal Cognitive Assessment (MoCA-T) and a battery of neuropsychological tests were assessed at baseline and at a two-year follow-up. The cross-culture modified Sniffin’ Sticks Identification Test (SSIT) was utilized to measure olfactory function. Generalized linear mixed models were used to examine the association of olfaction with cognitive performance over two years. Results: Data were collected from 376 participants (55.1% women), with a mean age of 75.6 years. A one-point decrease in the SSIT score (worsening of olfaction) was associated with worse global cognition (MoCA-T: β ˆ = –0.13), memory ( β ˆ = –0.08 to –0.06), and verbal fluency ( β ˆ = –0.07). Compared with an SSIT score ≥ 11 (normosmia), an SSIT score < 8 (anosmia) was associated with worse global cognition (MoCA-T: β ˆ = –0.99), memory ( β ˆ = –0.48 to –0.42), executive function (Trail Making Test A: β ˆ = –0.36), attention (digit span backward: β ˆ = –0.34), and verbal fluency ( β ˆ = –0.45). After stratified analyses, the associations remained in older adults ≥ 75 years, males, and non-carriers of apolipoprotein E ɛ4 in terms of global cognition, memory, and verbal fluency. Conclusions: Odor identification deficits were associated with poor global or domain-specific cognitive function in a four-year cohort of community-dwelling older adults. Cognitive assessments should be conducted in dementia-free elderly individuals with impaired odor identification.