3. Results
The demographic and clinical characteristics of the enrolled subjects are summarized in Table 1. Table 1 presents the descriptive statistics from the objective test-based gustatory dysfunction perspective. In total, 180 subjects were identified as having normal gustatory function, and 39 were identified as having gustatory dysfunction. The mean age was 46.0 ± 18.8 years in the normal gustatory function group and 56.5 ± 18.1 years in the gustatory dysfunction group. The difference in age between the two groups was statistically significant (p = 0.0016). The composition of sex and the prevalence of diabetes mellitus (DM) were statistically significant (p = 0.001). The prevalence of hypertension and the proportion of smokers were not different between the two groups.
Regarding subjective olfactory function, the proportions of subjective normosmia, hyposmia, and anosmia in the normal gustatory function group were 8.3%, 20%, and 71.7%, respectively. In the gustatory dysfunction group, the proportions of subjective normosmia, hyposmia, and anosmia were 38.5%, 25.6%, and 35.9%, respectively. There was a statistically significant difference between the two groups (p < 0.0001). Regarding objective test-based olfactory function, the proportions of normosmia, hyposmia, and anosmia were 43.3%, 18.3%, and 38.4%, respectively, in the normal gustatory function group. In the gustatory dysfunction group, the proportions of normosmia, hyposmia, and anosmia were 46.2%, 33.3%, and 20.5%, respectively. There was a statistically significant difference between the two groups (p = 0.041). The mean threshold, discrimination, identification, and TDI scores also significantly differed between the two groups (p< 0.0001).
Next, the relationships between objective gustatory function and the other variables were evaluated. Among the exploratory variables, age, sex (male), DM, subjective olfactory function, threshold, discrimination, identification, and TDI scores were significantly associated with the presence of objective gustatory dysfunction in the univariate analysis (Table 2). In the multivariate analysis, age, sex, objective olfactory function, threshold, and discrimination score were selected based on the AIC criteria. Age, sex (male), and objective olfactory function were positively associated with objective gustatory dysfunction, and the threshold and discrimination score were negatively associated with objective gustatory dysfunction. However, when the relationships between subjectively recognized gustatory function and other variables were evaluated, smoking (p = 0.028) and subjective olfactory function (p = 0.007) were positively associated with subjective gustatory dysfunction in the univariate and multivariate analyses (Supplementary Table 1). Figure 1 shows the violin plots for the continuous variables (age, threshold, discrimination, identification, and TDI) for the objective gustatory function. As shown by the mean and variance information in Table 2 and Supplementary Table 2, there were no significant differences among the continuous variables for subjective gustatory dysfunction (Figure 1A). However, for the test-based objective gustatory function, differences were observed in all the continuous variables (Figure 1B). Significant differences were observed in the threshold, discrimination, identification, and TDI. This was confirmed by the fact that the p -values for these variables were less than 0.0001 (Table 2).
Finally, the relationships between objective gustatory function and other clinical variables were investigated according to age (age ≥ 60 years and age < 60). Since there were only two patients with hypertension in the under 60 group, the logistic regression did not converge, and hypertension was excluded from the analysis. In the group aged less than 60, subjective olfactory function, threshold, discrimination, identification, and TDI score were significant variables in the univariate analysis, and sex (male) (p = 0.046) was positively associated with objective gustatory dysfunction and the threshold score (p = 0.013) and discrimination score (p = 0.010) were negatively associated with objective gustatory dysfunction in the multivariate analysis. In the group aged ≥ 60 years, sex (male), subjective olfactory function, threshold, identification, and TDI score were significant variables in the univariate analysis. Sex (male) (p = 0.012) was positively associated with objective gustatory dysfunction, and the threshold score (p = 0.0312) was negatively associated with objective gustatory dysfunction in the multivariate analysis (Table 3).