Olfactory dysfunction is a risk factor for the comorbidity of mild cognitive impairment and Type 2 diabetes mellitus.

Objectives: Diabetes can accelerate cognitive decline and hence affect the prognosis of patients with Type 2 diabetes mellitus (T2DM). Olfactory assessment can facilitate the early identification of cognitive impairment among T2DM patients. This study aims to evaluate the effects of olfactory function on mild cognitive impairment (MCI) in patients with T2DM.

Methods: A total of 472 T2DM patients who were hospitalized in a first-class hospital in Changsha City from June 2018 to June 2019 were enrolled for this study. Olfactory function and cognitive function were assessed by the alcohol sniff test and the Montreal Cognitive Assessment (MoCA) scale, respectively. Participants were categorized into a comorbidity of MCI and T2DM group and a T2DM group. General information was collected and some biochemical indices were tested. Difference in the alcohol sniff test score between the 2 groups was assessed by 2-sample -test. Difference in the presence of olfactory dysfunction between the 2 groups was assessed by test, and multivariable logistic regression was used to determine the relevant factors contributing to the comorbidity of MCI and T2DM.

Results: Of the 472 participants, 162 were identified with MCI, making the comorbidity rate at 34.3%. Values of isopropyl alcohol sniff test were significantly different between the 2 groups [(9.15±3.22) cm vs (21.03±4.36) cm, <0.05]. The number of patients with olfactory dysfunction also differed significantly between the 2 groups (120 vs 50). After adjustment for age, educational level, T2DM duration, fasting insulin, and glycosylated hemoglobin (HbA1c), multivariate logistic regression analysis showed older age (OR=1.14, 95% CI 1.09 to 1.20), longer course of diabetes (OR=1.21, 95% CI 1.12 to 1.31), and olfactory-impaired (OR=4.61, 95% CI 3.04 to 6.18) were independent risk factors for T2DM combined with MCI, and the high education level (OR=0.26, 95% CI 0.15 to 0.38) was an independent protective factor for T2DM combined with MCI.

Conclusions: Olfactory dysfunction is an independent risk factor for the comorbidity of MCI and T2DM. Special attention should be paid to those with olfactory dysfunction when carrying out cognitive interventions in T2DM patients.