Inability to Smell Peppermint Is Related to Cognitive Decline: A Prospective Community-Based Study

Abstract

Background: A few studies have demonstrated the association of poorer olfactory identification (OI) with poorer cognition in population-based cohorts. None of them considered the outcome associated with the inability to smell a certain odor. Objective: To verify the hypothesis that at least one specific odor is associated with incident cognitive decline among older adults. Methods: In the Shanghai Aging Study, a sub-cohort of 948 dementia-free participants who had baseline OI measurements were prospectively followed for 5 years. Results: An inability to smell peppermint (β = -0.44, p < 0.001), rose (β = -0.14, p = 0.040), or coffee (β = -0.37, p = 0.002) was inversely related to the annual rate of change in the Mini Mental State Examination score, and an inability to smell peppermint was associated with a higher risk for incident dementia (hazard ratio 2.67, 95% CI 1.44-4.96) after adjustment for confounders. Conclusion: Our study suggests that some odors, especially peppermint, might be considered as a potential predictor for dementia in older populations. Inability to Smell Peppermint and Cognitive Decline

Predictive Value of Odor Identification for Incident Dementia: The Shanghai Aging Study

“…Some studies suggest that olfactory dysfunction could be a suitable biomarker for predicting cognitive impairment and development of dementia (Suzuki et al, 2004;Eibenstein et al, 2005;Devanand et al, 2015;Ottaviano et al, 2016;Roberts et al, 2016;Roalf et al, 2017). Our previous study also indicates that some odors, such as peppermint in the OI test, are associated with incident dementia in the older population (Liang et al, 2020). However, the predictive ability of the models incorporating the OI test was not ideal in previous studies.…”

“…At the baseline of our Shanghai Aging Study, we found a lower score on the olfactory identification (OI) test and a reduced ability to identify odors of peppermint, orange, pineapple, cinnamon, coffee, fish, banana, rose, leather, and licorice in participants with MCI compared to those with normal cognition (Liang et al, 2016). We further verified these findings in the 5-year prospective phase and explored the association of inability to smell peppermint with a higher dementia onset risk (HR = 2.67, 95% CI: 1.44, 4.96) by using a multivariable logistic regression (MLR) model (Liang et al, 2020). However, the previous study also did not evaluate the performance (or predictive value) of peppermint in predicting incident dementia.…”

“…The Shanghai Aging Study is a prospective cohort study aiming to enumerate the prevalence, incidence, and risk factors for dementia and MCI among residents aged ≥60 in an urban community of central Shanghai. The study design and participant recruitment of SAS are described in detail elsewhere (Ding et al, 2014;Liang et al, 2016;Liang et al, 2020). A flowchart of recruitment for study participants is shown in Supplementary Figure S1.…”

“…Medical history: Participants' medical histories, including physician-diagnosed hypertension, coronary artery disease (CAD), diabetes, and stroke were asked by neurologists from the Department of Neurology, Huashan Hospital (Liang et al, 2020).…”

“…Detailed baseline information on the participants is published elsewhere and given in Supplementary Table S1 (Liang et al, 2020). In general, compared to those who did develop dementia (n = 872), participants with incident dementia (n = 75) were older (77.8 vs 69.9 years), shorter (156.5 vs 162.0 cm), weighed less (59.1 vs 64.4 kg), and had less education (9 vs 12 years) when recruited.…”