Association between olfactory function and cognitive impairment in dementia‐free older adults in Taiwan: A longitudinal cohort study

Abstract

AbstractBackgroundThe olfactory impairment could be one of the earliest signs of cognitive impairment. However, limited studies have evaluated olfactory function and cognitive domains in Asian older adults. This study aimed to relate olfaction with global and domain‐specific cognition in Taiwan’s community‐dwelling, non‐demented older adults.MethodThis cohort study is part of the Taiwan Initiative for Geriatric Epidemiological Research, including 310 non‐demented older adults between 2015‐2019 with two repeated measures on cognitive function. Global and domain‐specific (memory, executive function, attention, and language) cognition were assessed by the Taiwanese version of Montreal Cognitive Assessment (MoCA‐T) and a battery of neuropsychological tests, respectively. The Sniffin' Sticks‐Odor Identification Test (SS‐OIT) was utilized to identify impaired olfaction. The generalized linear mixed model was used to examine the association of SS‐OIT with cognitive function over time, after adjustment for age, sex, years of education, apolipoprotein E ε4 status, presence of depression, sleep quality, chronic respiratory diseases, smoking, practice effect and follow‐up time. Subgroup analyses were also conducted.ResultBetter olfactory identification ability (i.e., increased SS‐OIT score) was associated with better performance of global cognition (MoCA‐T: β = 0.14, 95% confidence interval = 0.05‐0.24), memory (logical memory ‐ immediate and delayed theme and free recall: β = 0.06 to 0.09), executive function (trail making test‐A: β = 0.05 for baseline, ‐0.03 for interaction with follow‐up years), and verbal fluency (β = 0.08). Anosmia (SS‐OIT score ≦8) was associated with impaired memory [the lowest tertile (T1) vs. higher tertiles (T2+T3), adjusted odds ratio (aOR): 2.40 to 3.06], and verbal fluency (T1 vs. T2+T3, aOR = 2.39). After stratified analyses, the associations above remained significant in apolipoprotein E ε4 non‐carriers (MoCA‐T: β = 0.19; memory: β = 0.08 to 0.11; verbal fluency: β = 0.08), older adults without respiratory diseases (MoCA‐T: β = 0.14; memory: β = 0.06 to 0.10; verbal fluency: β = 0.10), and older adults without depression (MoCA‐T: β = 0.14; memory: β = 0.06 to 0.09; trail making test‐A: β = 0.04 for baseline, ‐0.02 for interaction with follow‐up years; verbal fluency: β = 0.09).ConclusionImpaired olfactory identification is associated with poor global or domain‐specific cognition in non‐demented older adults. Further research is required to validate our findings and clarify the underlying mechanism between anosmia and cognitive impairment.