Relationship between olfactory dysfunction and cognitive impairment in elderly patients with type 2 diabetes mellitus

Aims: Recent clinical studies identified the relation between olfactory dysfunction and cognitive impairment in the elderly without type 2 diabetes mellitus. The aim of the present study was to define the relation between olfactory function and cognition in elderly patients with type 2 diabetes mellitus.

Methods: The study participants comprised 250 elderly (age, 68-77, median 72) Japanese outpatient with type 2 diabetes mellitus free of clinically-evident cognitive impairment. Olfactory and cognitive functions were evaluated by the Open Essence (OE) test and Mini-mental State Examination (MMSE), respectively.

Results: Based on the MMSE score, 62.0%, 24.4%, and 13.6% of the participants were considered to have no impairment, possible cognitive impairment and probable dementia, respectively. The OE test score of the probable dementia group was significantly lower than other groups. Furthermore, age and serum uric acid were significantly higher in the probable dementia group than other groups. Simple correlation analysis showed positive correlation between the MMSE score and diastolic blood pressure, education, OE test score, total cholesterol, LDL cholesterol, folic acid, and negative correlation with age, HbA1c, aspartate aminotransferase, serum adiponectin and urinary albumin excretion. Multivariate regression analysis showed that OE test score correlated significantly and independently with MMSE score (standardized coefficients β=0.542, R(2)=0.478, P<0.01), in addition to education level, HbA1c and serum adiponectin.

Conclusions: The results suggested the association of olfactory dysfunction with cognitive impairment in elderly patients with type 2 diabetes mellitus.