Demographic characteristics
After strict observance of the inclusion and exclusion criterion, a total of 219 individuals were enrolled in this study, including 98 men (44.7%; mean age, 63.08±6.64 years) and 121 women (55.3%; mean age, 62.64±7.17 years). With regard to HL, 64(29.2%) participants had normal hearing, 70(32.0%) had mild HL, 73(33.3%) had moderate HL, and 12(5.5%) had severe-profound HL (severe and profound HL groups were combined because of the small sample size). Participant age, duration of HL, PTA, and the speech recognition rate differedamong the four groups. Individuals with worse hearing were typically older, had had HL for a longer time, had a higher PTA, and had a worse speech recognitionrate than those with better hearing. However, there were no differences in sex, educational level, or occupation type among the groups. The specific sociodemographic and hearing characteristics of the participants are summarized in Table 1.
Table 1. Socio-demographic characteristics of all participants by hearing loss degree
Characteristics
|
Hearing-loss degree
|
P Value
|
Normal
(n=64)
|
Mild
(n=70)
|
Moderate
(n=73)
|
Severe-profound
(n=12)
|
Age, mean (SD), years
|
59.92(4.62)
|
63.23(6.83)
|
64.42(7.51)
|
66.42(9.22)
|
0.001
|
Sex, n (%)
|
|
|
|
|
|
Male
|
23(23.47)
|
33(33.67)
|
37(37.75)
|
5(5.10)
|
0.146
|
Female
|
41(33.88)
|
37(30.58)
|
36(29.75)
|
7(5.79)
|
|
Education, n (%)
|
|
|
|
|
|
Illiteracy
|
2(16.67)
|
3(25.00)
|
5(41.67)
|
2(16.67)
|
|
Primary school
|
6(23.08)
|
9(34.62)
|
11(42.31)
|
0(0.00)
|
0.249
|
Junior/ high school
|
36(29.51)
|
36(29.51)
|
42(34.43)
|
8(6.56)
|
|
Undergraduate/ master/ PhD
|
20(33.90)
|
22(37.29)
|
15(25.42)
|
2(3.39)
|
|
Occupation type
|
|
|
|
|
|
None
|
18(29.03)
|
18(29.03)
|
20(32.26)
|
6(9.68)
|
0.668
|
Retired
|
35(32.71)
|
33(30.84)
|
36(33.64)
|
3(2.80)
|
|
Physical labor
|
6(24.00)
|
9(36.00)
|
8(32.00)
|
2(8.00)
|
|
Mental labor
|
5(20.00)
|
10(40.00)
|
9(36.00)
|
1(4.00)
|
|
Duration of HL, mean (SD), years
|
0.33(1.37)
|
1.87(4.47)
|
5.91(11.23)
|
13.21(15.15)
|
0.000
|
PTA, mean (SD), dB HL
|
15.94(4.71)
|
31.18(5.40)
|
49.38(5.78)
|
66.87(10.92)
|
0.000
|
Speech recognition rate, mean (SD), %
|
98.56(2.61)
|
94.57(10.64)
|
49.38(5.78)
|
66.88(10.92)
|
0.000
|
SD, standard deviation; dB HL, decibel hearing level; PTA, pure-tone thresholds average
Association between cognition and hearing
The overall MMSE scores of the normal hearing andmild, moderate, and severe-profound HL groups were 24.53±3.10, 24.36±3.92, 23.32±3.88, and 20.92±6.53, respectively. There was no significant association between MMSE score and the degree of HL (p=0.09). Linear regression analysis revealed that the MMSE score was negatively correlated tothe PTA (R2=0.07, p<0.001, Figure 1) and positively related to the speech recognition rate (R2=0.09, p<0.001, Figure 2).
Association between cognition and educational level
MMSE scores were higher among participants with higher educational levels (p<0.001). The overall MMSE scores of the illiterate, primary-school, junior/high-school, and undergraduate/master’s/PhD groups were 16.67±3.87, 20.35±3.46, 24.16±3.23, and 26.31±2.49, respectively. The above trend among the four education levels was also present in the MMSE subdomains of orientation (p<0.001), attention and calculation (p<0.001), recall (p<0.001), and language (p<0.001),but not in that of registration (p=0.142, Figure 3).
Association between cognition and occupation
MMSE scores were significantly correlated with occupation type (p<0.001). The overall MMSE scores of the unemployed, retired, physical labor, and mental labor groups were 22.00±4.53, 24.94±2.84, 26.28±2.64, and 21.52±4.52, respectively. The distribution of the overall MMSE score and those for different occupation types is illustrated in Figure 4.
Association between cognition and sex
MMSE scores were significantly higher in men than in women (p<0.001). However, uponanalysis of the five subdomains, significant differenceswere only observed for attention and calculation (p<0.001) and language (p=0.011). Scores did not differ between sexes in terms of orientation (p=0.091), registration (p=0.985), or recall (p=0.128) (Figure 5).We further exploredwhether educational level is related to the cognitive differences between the sexesby comparing the distribution of educational levels between men and women, with the chi-squared test.Thisanalysis revealed no significant difference in the educational levelbetween the sexes (p=0.070, Table 2).
Table 2. The distribution difference of educational level between males and females
Sex, n (%)
|
Education level
|
P-value
|
Illiteracy
|
Primary school
|
Junior/ high school
|
Undergraduate/ master/ PhD
|
Male
|
2(2.04)
|
9(9.18)
|
55(56.12)
|
32(32.65)
|
0.070
|
Female
|
10(8.26)
|
17(14.05)
|
67(55.37)
|
27(22.21)
|
|
Association of MMSE score with measured characteristics
Table 3 summarizes the results of the linear regression analyses. In the univariable analysis, the MMSE score was significantly associated with sex, educational level, occupation type, duration of HL, PTA, and speech recognition rate (all p<0.05). In the multivariable analysis, the duration of HL (p=0.794) and PTA (p=0.212) were excluded from the model. MMSE scores of retired participants and those with a physical job did not differ from those of unemployed participants (p=0.872 and p=0.239, respectively).
Table 3. Association of MMSE score with measured characteristics in the simple and multiple linear regression analysis
Characteristics
|
Univariate analysis
|
Multivariate analysis
|
β
|
95% CI
|
P Value
|
β
|
95% CI
|
P Value
|
Age
|
-0.06
|
-0.14, -0.01
|
0.096
|
-0.027
|
-
|
0.612
|
Sex
|
|
|
|
|
|
|
Male
|
Reference
|
|
|
-
|
-
|
-
|
Female
|
-1.82
|
-2.85, -0.79
|
0.001
|
-1.30
|
-2.11, -0.50
|
0.002
|
Education
|
|
|
|
|
|
|
Illiteracy
|
Reference
|
|
|
-
|
-
|
-
|
Primary school
|
3.68
|
1.54, 5.82
|
0.001
|
2.79
|
0.73, 4.85
|
0.008
|
Junior/ high school
|
7.49
|
5.63, 9.35
|
<0.001
|
6.46
|
4.67, 8.23
|
<0.001
|
Undergraduate/ master/ PhD
|
9.638
|
7.69, 11.58
|
<0.001
|
8.13
|
6.24, 10.02
|
<0.001
|
Occupation type
|
|
|
|
|
|
|
None
|
Reference
|
|
|
|
|
|
Retired
|
2.94
|
1.82, 4.07
|
<0.001
|
0.01
|
-
|
0.872
|
Physical labor
|
4.28
|
2.60, 5.96
|
<0.001
|
0.07
|
-
|
0.239
|
Mental labor
|
-0.48
|
-2.16, 1.20
|
0.573
|
-1.92
|
-3.17, -0.66
|
0.003
|
Duration of hearing loss
|
-0.08
|
-0.14, 0.01
|
0.02
|
-0.01
|
-
|
0.794
|
PTA
|
-0.07
|
-0.10, 0.03
|
<0.001
|
-0.08
|
-
|
0.212
|
Speech recognition rate
|
0.07
|
0.04, 0.10
|
<0.001
|
0.05
|
0.03. 0.08
|
<0.001
|
β, regression coefficient; CI, confidence interval; PTA, pure-tone thresholds average.