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Neurology. 2019 Feb 12;92(7):e700-e709. doi: 10.1212/WNL.0000000000006919. Epub 2019 Jan 16.

Impaired olfaction is associated with cognitive decline and neurodegeneration in the brain.

Author information

1
From the Aging Research Center (C.S.D., A.M., D.R., R.W., J.S., W.X.), Department of Neurobiology, Care Sciences and Society, Karolinska Institutet and Stockholm University; Department of Clinical Neuroscience (J.S.), Psychology Division, Karolinska Institutet, Stockholm, Sweden; Department of Biomedical Engineering (K.A.), Illinois Institute of Technology, Chicago; Rush Alzheimer's Disease Center (K.A., D.A.B.), and Department of Neurological Sciences (D.A.B.), Rush University Medical Center, Chicago, IL; and Department of Epidemiology and Biostatistics (W.X.), School of Public Health, Tianjin Medical University, China. christina.dintica@ki.se xuweili@tmu.edu.cn.
2
From the Aging Research Center (C.S.D., A.M., D.R., R.W., J.S., W.X.), Department of Neurobiology, Care Sciences and Society, Karolinska Institutet and Stockholm University; Department of Clinical Neuroscience (J.S.), Psychology Division, Karolinska Institutet, Stockholm, Sweden; Department of Biomedical Engineering (K.A.), Illinois Institute of Technology, Chicago; Rush Alzheimer's Disease Center (K.A., D.A.B.), and Department of Neurological Sciences (D.A.B.), Rush University Medical Center, Chicago, IL; and Department of Epidemiology and Biostatistics (W.X.), School of Public Health, Tianjin Medical University, China.

Abstract

OBJECTIVE:

We aimed to examine whether impaired olfaction is associated with cognitive decline and indicators of neurodegeneration in the brain of dementia-free older adults.

METHODS:

Within the Rush Memory and Aging Project, 380 dementia-free participants (mean age = 78 years) were followed for up to 15 years, and underwent MRI scans. Olfactory function was assessed using the Brief Smell Identification Test (B-SIT) at baseline, and categorized as anosmia (B-SIT <6), hyposmia (B-SIT 6-10 in men and 6-10.25 in women), and normal (B-SIT 10.25-12 in men and 10.5-12 in women). Cognitive function was annually assessed with a battery of 21 tests, from which composite scores were derived. Structural total and regional brain volumes were estimated. Data were analyzed using linear regression and mixed-effects models.

RESULTS:

At study entry, 138 (36.3%) had normal olfactory function, 213 (56.1%) had hyposmia, and 29 (7.6%) had anosmia. In multiadjusted mixed-effects models, hyposmia (β = -0.03, 95% confidence interval [CI] -0.05 to -0.02) and anosmia (β = -0.13, 95% CI -0.16 to -0.09) were associated with faster rate of cognitive decline compared to normal olfaction. On MRI, impaired olfaction (hyposmia or anosmia) was related to smaller volumes of the hippocampus (β = -0.19, 95% CI -0.33 to -0.05), and in the entorhinal (β = -0.16, 95% CI -0.24 to -0.08), fusiform (β = -0.45, 95% CI -0.78 to -0.14), and middle temporal (β = -0.38, 95% CI -0.72 to -0.01) cortices.

CONCLUSION:

Impaired olfaction predicts faster cognitive decline and might indicate neurodegeneration in the brain among dementia-free older adults.

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