Patients with Alzheimer's disease (AD) develop olfactory and gustatory disorders. However, the order of failure and relevance of the pathophysiology are unclear. We compared olfactory identification and whole mouth gustation in patients with AD to those with mild cognitive impairment (MCI) and to healthy controls (HC) and assessed correlations with pathophysiology. Patients with AD (n = 40), MCI (n = 34), and HC (n = 40) were recruited. We performed the Odor Stick Identification Test for Japanese (OSIT-J), gustatory test by the intraoral dropping method using taste solutions, Mini-Mental State Examination (MMSE), Alzheimer's Disease Assessment Scale-cognitive subscale Japanese version (ADAS-J cog), Touch Panel-type Dementia Assessment Scale (TDAS), and measurement of amyloid β (Aβ) 42 and phosphorylated tau (p-tau) 181 levels in cerebrospinal fluid (CSF). Patients with AD and MCI had lower OSIT-J scores than did the HC. The OSIT-J score was correlated with the MMSE, ADAS-J cog, TDAS, and Aβ42 results. There were no significant differences in the gustatory test scores among the three groups. The gustatory test score was only correlated with the MMSE, ADAS-J cog, and TDAS results. Olfactory function decreased in AD and MCI patients and was associated with CSF biomarker levels and cognitive disorders. The results suggest that olfactory function is impaired in early stage of AD. Gustatory function was not correlated with CSF biomarkers, which suggests that it may not be impaired in early stage of AD.

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Background/objectivesThis study assessed the effect of continuous ingestion of monosodium l-glutamate (MSG) on cognitive function and dietary score in dementia patients.Subjects/methodsThis was a single-blind, placebo-controlled trial involving 159 subjects with dementia residing in a hospital or nursing home. We assigned the subjects to a group that ingested MSG thrice daily (0.9 g/dose) (MSG group; n = 79) or a group that ingested NaCl thrice daily (0.26 g/dose) (Control group; n = 80). This study consisted of a 12-week intake period, followed by a 4-week follow-up period without the ingestion of MSG or NaCl. We performed physical examination, cognitive symptom tests (the Touch Panel-type Dementia Assessment Scale (TDAS) and Gottfries–Bråne–Steen Scale (GBSS)), palatability and behaviour questionnaires, and blood tests before and after the intervention and after the follow-up period.ResultsThere were no significant differences in the TDAS and GBSS total scores between the groups before and after the intervention. However, regarding the TDAS sub-items, “the accuracy of the order of a process” did not deteriorate in the MSG group compared with that observed in the Control group (p < 0.05). At the follow-up assessment, the TDAS total scores in the MSG group showed significant improvement compared with those reported in the Control group (p < 0.05). Furthermore, there was a correlation of changes from pre-intervention to post-intervention between the TDAS and enjoyment of the meal (r = −0.299, p = 0.049).ConclusionsOur results suggest that continued ingestion of MSG has an effect on cognitive function. Furthermore, the patients with improved questionnaires about palatability survey showed greater improvement in cognitive function.