Decline of gustatory sensitivity with the progression of Alzheimer's disease

Patients with Alzheimer's disease (AD) manifest various impairments in eating behavior. However, few previous studies have directly investigated the gustatory function of AD patients, and results have been inconsistent. Thirty-two AD patients (Clinical Dementia Rating (CDR) 0.5/1/2, respectively 11/15/6 patients) and 22 normal control participants were examined to measure detection and recognition thresholds of the four elemental tastes (sweet, salty, sour, and bitter), and their ability to discriminate between tastes. Effects of demographic and clinical factors (age, sex, histories of alcohol and tobacco consumption, and CDR grade) on gustatory threshold were examined using ordinal logistic regression analysis. Performance was compared between AD and control groups. Total threshold values (the sum of threshold grades for the four tastes) for detection and recognition of tastes were significantly higher in the AD group. Detection thresholds for sweet, salty, and bitter, and recognition thresholds for sweet and sour, were also significantly higher in the AD group. Ordinal logistic regression analysis revealed that CDR grade was the only factor that significantly affected both total threshold values. Regarding taste discrimination, there were no significant differences between the AD group and control group. These findings suggest that progression of dementia severity accompanies gustatory decline. Although it seemingly paradoxical, weight loss and preference for sweet tastes are frequently, often simultaneously, observed in AD. Gustatory dysfunction may be partially involved in these symptoms. Thus, the nutritional care of patients with AD could be improved by making the taste of meals stronger, while controlling calorie and mineral intake.