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Oral status, primarily marked by tooth loss, is critical for maintaining physical, mental, and social wellbeing (1), especially in later life. Prevalence and incidence estimates of severe tooth loss increased gradually with age (2). Meanwhile, late-life depression is a significant public health problem, which can often result in personal suffering, family disruption, and the deterioration of many medical disorders (3). The relationship between oral status and depressive symptoms among older adults, while receiving increasing amounts of attention, has not yet been studied conclusively. Some research based on American adults found that tooth loss was associated with depression (4). However, some studies reported that poor dental health was not significantly associated with depressive symptoms among the elderly (5). The evidence about the relation between oral status and late-life depression is still limited and inconsistent. Additionally, although there are a few cross-sectional results focusing on Chinese older adults (6), more longitudinal studies are still needed to target the association between oral status, including tooth loss and denture use, and depressive symptoms among Chinese older adults.
Therefore, this study aims to explore the relationship between oral status, including tooth loss and denture use, and depressive symptoms among older Chinese adults using data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). Furthermore, the combined association of tooth loss and denture use with depressive symptoms was explored as well as interaction effects by different demographic and behavioural characteristics.
The data used in this paper came from CLHLS. Focusing on the older population aged 65 and above, the CLHLS was conducted in 1998–2018 from randomly selected counties and cities of 22 out of 31 provincial-level administrative divisions (PLADs) in China (7). We used 2 waves of CLHLS data conducted in 2014 and 2018 to analyze how tooth loss and denture use in 2014 influenced depressive symptoms 4 years later (8). Overall, 3,310 out of 7,192 eligible participants were included for analyses after excluding cases lost to follow-up and with missing information on key variables (see Supplementary Figure S1 for the variable screening process. We collected the self-reported number of natural teeth and classified the participants into 4 categories (0, 1–9, 10–19, and 20 and above). A five-item scale, which has been applied in several studies to represent depressive symptoms via the CLHLS data (9), was adopted in the CLHLS to evaluate depressive symptoms with higher values indicating more depressive symptoms. The definitions of other variables are shown in the Supplementary Materials.
Supplementary Table S1 shows baseline characteristics of elderly by numbers of natural teeth and denture use. The mean age of the participants was 81.29 (SD=10.32), 46.99% were male, 39.13% had an urban residence, 71.60% of the participants had 19 teeth or less, and 28.40% had completely no teeth. The denture use rate was 39.40%. The mean of depressive symptom scores was 6.78 (SD=3.19) and increased with tooth loss. Participants using dentures had lower depressive symptom scores compared with those without the denture. Supplementary Table S2 further demonstrate depressive Symptom Scores of the participants in 2018 by Covariates.
This study followed a stepwise approach and applied multivariable linear models to adjust for confounding variables to clarify the effects of oral status on depressive symptoms. Model 1 only included categories of natural teeth numbers and denture use. Model 2 adjusted for the demographic and socioeconomic covariates, such as age, gender, ethnicity, marital status, residence, education, and pension. Model 3 further added the covariates of lifestyle, including smoking, alcohol consumption, fruit intake, vegetable intake, and health conditions including Activities of Daily Living (ADL) and Mini-Mental State Examination (MMSE) score. Model 4 further controlled for variables of social engagement, including playing cards or mahjong, participation in community activities, and travel. Model 4 was identified as a fully adjusted model. Subgroup analysis was conducted to assess differences between groups. The mediation effects were tested by adding interaction terms of the number of natural teeth and age (65–79 years or ≥80 years), gender, ethnicity, smoking, drinking, and denture use. All statistical analyses were performed using the STATA 16 software (MP version16.0, StataCorp LLC, USA). P<0.05 was considered to be statistically significant.
Table 1 presented the regression results of the associations of the numbers of natural teeth and status of denture use with depressive symptoms. The depressive symptom scores increased and slightly decreased as the numbers of teeth decreased (P for trend <0.001). For the fully adjusted model, individuals with 10–19, 1–9, and 0 teeth had 0.55, 0.59, and 0.33 point higher scores of depressive symptoms than those with 20+ teeth, respectively (all P<0.01). The denture users had an adjusted lower score of 0.27 points (P<0.01) compared with people without dentures.
Item Coefficient (95% CI) for depressive symptom (N=3,310) Model 1 Model 2 Model 3 Model 4 Number of natural teeth 20+ Reference Reference Reference Reference 10–19 0.95 (0.90, 1.25)*** 0.62 (0.35, 0.71)*** 0.57 (0.34, 0.70)*** 0.55 (0.32, 0.68)*** 1–9 1.21 (1.29, 1.60)*** 0.69 (0.42, 0.77)*** 0.60 (0.32, 0.67)*** 0.59 (0.30, 0.65)*** 0 1.15 (1.25, 1.57)*** 0.47 (0.21, 0.59)*** 0.37 (0.06, 0.44)** 0.33 (0.03, 0.41)** P for trend <0.001 <0.001 <0.001 <0.001 Denture use No Reference Reference Reference Reference Yes −0.83 (−0.96, −0.71)*** −0.40 (−0.50,−0.24)*** −0.24 (−0.36, −0.09)*** −0.27 (−0.32, −0.06)** Abbreviation: CI=confidence interval.
* P≤0.05.
** P≤0.01.
*** P≤0.001.Table 1. Association between number of natural teeth, denture use, and depressive symptom scores among Chinese older adults — China, 2014–2018.
As the association of the interaction of tooth loss and denture use with depressive symptoms was significant (Table 2; P for interaction <0.001), we showed the combined effects of tooth loss and denture use on depressive symptoms in Table 3. Among non-denture users, scores of depressive symptoms compared with those who had 20+ teeth with/without dentures were 0.64 and 0.61 points higher for older adults with 10–19 teeth and 1–9 teeth, respectively (all P<0.001). Denture users had a lower score than non-users in the category of 1–9 teeth. However, there was no significant difference between denture/non-denture users with 20 teeth and denture users with 10–19 teeth, as well as non-denture users with 0 teeth. It is worth noting that denture users with 0 teeth as compared with those with 20+ teeth still had a significantly higher score of depressive symptoms (coefficient=0.20, P<0.05).
Oral status Coefficient (95% CI) for depressive symptom (N=3,310) Model 1 Model 2 Model 3 Model 4 20+ teeth Reference Reference Reference Reference 10–19 teeth with dentures 0.15 (−0.22, 0.53) 0.17 (−0.12, 0.71) 0.15 (−0.12, 0.69) 0.18 (−0.12, 0.69) 10–19 teeth without dentures 1.10 (0·99, 1·38)*** 0.71 (0.40, 0.79)*** 0.66 (0.39, 0.79)*** 0.64 (0.40, 0.87)*** 1–9 teeth with dentures 0.42 (0.12, 0.73)** 0.32 (0.02, 0.62)* 0.35 (0.26, 0.98)** 0.37 (0.23, 0.96)* 1–9 teeth without dentures 1.37 (1.15, 1.59)*** 0.76 (0.52, 0.99)*** 0.64 (0.40, 0.87)*** 0.61 (0.38, 0.85)*** 0 teeth with dentures 0.49 (0.25, 0.72)*** 0.18 (−0.06, 0.42) 0.22 (0.11, 0.79)* 0.20 (0.04, 0.45)* 0 teeth without dentures 1.21 (0.93, 1.48)*** 0.43 (0.13, 0.56)** 0.25 (−0.11, 0.33) 0.23 (−0.13, 0.31) Abbreviation: CI=confidence interval.
* P≤0.05.
** P≤0.01
*** P≤0.001.Table 2. The combined effects of tooth loss and denture use on depressive symptom scores among Chinese older adults — China, 2014–2018.
Subgroup Number of natural teeth (95% CI) P for interaction 0 1–9 10–19 20+ Age <0.001 65–79 years 0.48 (0.17, 0.79)** 0.31 (0.05, 0.58)* 0.55 (0.32, 0.78)*** Reference ≥80 years 0.16 (−0.11, 0.44) 0.54 (0.28, 0.80)*** 0.49 (0.20, 0.77)** Reference Gender 0.021 Women 0.14 (−0.14, 0.42) 0.42 (0.15, 0.68)*** 0.53 (0.26, 0.80)*** Reference Men 0.29 (0.02, 0.55)* 0.51 (0.28, 0.75)*** 0.42 (0.18, 0.66)*** Reference Ethnicity 0.548 Han 0.28 (0.01, 0.41)* 0.58 (0.30, 0.67)*** 0.57 (0.29, 0.66)*** Reference Minorities 0.59 (−0.16, 1.19) 0.62 (−0.21−0.95)* 0.97 (0.12, 1.29)** Reference Smoking 0.107 Never smoke 0.19 (−0.21, 0.58) 0.78 (0.34, 1.21)*** 0.47 (0.24, 0.70)*** Reference All the time 0.18 (−0.21, 056) 0.78 (0.35, 1.21)*** 0.48 (0.26, 0.71)*** Reference Stop smoking 0.35 (−0.06, 0.76) 0.36 (−0.11, 0.83) 0.18 (−0.07, 0.43) Reference Drinking 0.309 Never drink 0.39 (−0.02, 0.80) 0.90 (0.42, 1.39)** 0.44 (0.22, 0.67)*** Reference All the time 0.19 (−0.22, 0.60) 0.64 (0.18, 1.10)** 0.53 (0.31, 0.75)*** Reference Stop drinking 0.29 (−0.16, 0.75) 0.24 (−0.29, 0.76) 0.23 (−0.01, 0.47)* Reference Denture use <0.001 Yes 0.60 (−0.15, 0.65)** 0.71 (0.21, 0.95) 0.48 (0.07, 0.77) Reference No 0.11 (0.35, 0.75)*** 0.51 (0.24, 0.65)*** 0.56 (−0.15, 0.33)* Reference Note: Coefficients were based on linear regression model 4. Effect modification by age (P for interaction <0.001), gender (P for interaction =0.021), and denture use (P for interaction <0.001).
Abbreviation: CI=confidence interval.
* P≤0.05.
** P≤0.01.
*** P≤0.001.Table 3. Subgroup analysis of the association between number of natural teeth and depressive symptom scores among Chinese older adults — China, 2014–2018.
No significant interaction effects were found in subgroup analyses for the number of natural teeth by ethnicity, smoking, and drinking (Table 3). Of note is that older adults with 1–9 teeth were associated with a higher depressive symptom score in the older elderly of 80+ (coefficient=0.54, P<0.001) than in the younger elderly of 65–79 years (coefficient=0.31, P<0.05), while there existed inverse relationship among people with no teeth and those with 10–19 teeth (P for interaction <0.001). In addition, the depressive symptom scores of men were higher than those of women with regard to people with 9 teeth or less, and the scores of women were higher than those of men for participants with 10–19 teeth (P for interaction =0.021).
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