Abstract
This cross-sectional study aimed to investigate the risk factors for low levels of subjective well-being (SWB) in the general population of Japan, specifically, the impact of the number of teeth and self-rated mastication. The surveyed population consisted of individuals aged between 40 and 79 years from Yamagata prefecture, Japan. A postal self-administered questionnaire survey of respondents lifestyles, medical history, oral health, and dietary intake, was conducted from 2017 to 2021. We included 6846 participants to confirm the independent associations between SWB and several parameters using multivariate ordinal logistic regression analysis to estimate adjusted odds ratios and 95% confidence intervals. Individuals with < 20 teeth and poor mastication ability had a 1.3-fold risk for low levels of SWB compared with individuals with ≥ 20 teeth with good mastication ability (adjusted odds ratios = 1.300, 95% confidence intervals = 1.043–1.621, P = .020). There were no differences between individuals with good mastication ability, regardless of the number of remaining teeth. Our study emphasizes not only the importance of having ≥ 20 teeth and good mastication ability for high levels of SWB but also the importance of restoring mastication ability using some form of prosthesis, to facilitate a high level of SWB when the number of remaining teeth is < 20.
Keywords: cross-sectional study, multivariate logistic regression analysis, number of teeth, self-rated mastication, subjective well-being
1. Introduction
Subjective well-being (SWB) is synonymous with self-rated happiness: being satisfied with one’s life, having a positive effect, and having little negative effect.[1] Although it could be said that SWB is subjective, the link between SWB and general health has been surveyed.[1,2] Several researchers have revealed that a low level of SWB is not only a result of poor health but also a potential risk factor for disease.[3–7] Furthermore, a high level of SWB has the potential to lower mortality compared with low levels of SWB.[4,8–11] Currently, high levels of SWB seem to positively affect general health.
The risk factors for low levels of SWB have also been surveyed. Poor psychological and physical condition are among the most well-known risk factors for low levels of SWB.[12] Furthermore, socio-ecological factors, such as low income and low educational status[13,14]; lifestyle-associated factors, such as poor sleep quality,[15] unhealthy dietary habits,[14,16,17] insufficient exercise,[13] smoking and alcohol habits,[18] and marital status[19] are well-known risk factors for low levels of SWB. Furthermore, self-rated health, which is also a subjective indicator, has been shown to be positively correlated with SWB.[20] In addition to these risk factors for low levels of SWB, associations between oral health and SWB have also been reported. The presence of dental caries, low frequency of dental-care utilization, malocclusion, and a high score of a subjective oral health assessment using the 14-item oral health impact profile were also well-reported risk factors for low levels of SWB.[21–24] Furthermore, in 2022, one of the largest studies to survey the associations between the number of remaining teeth and dental prosthesis use with SWB in 178,090 older people in Japan was reported.[20] This study revealed that having a higher number of teeth and using a dental prosthesis were factors independently associated with high levels of SWB.[20] However, the target population of these studies were adolescents or relatively older people aged > 65 years. To our knowledge, there have been no studies on the association between SWB and oral health targeting people of a wide age range in the general population. Moreover, to the best of our knowledge, no study has surveyed the association between SWB and the combination of the number of remaining teeth and self-rated mastication. Ideally, using a prosthesis with fewer teeth means restoration of masticatory function is performed well even if the number of remaining teeth is low; however, most dental clinicians know that cases of prosthetic incompatibility do occur. Using prostheses does not always mean good mastication. Therefore, we conducted a cross-sectional study, using data from the Yamagata community-based cohort study, to comprehensively identify the risk factors for low levels of SWB, focusing on the associations between SWB and the combination of the number of remaining teeth and self-rated mastication. The present study hypothesized that an association between low levels of SWB and fewer remaining teeth with poor self-rated mastication. The additional hypothesis of the present study was that a significant association exists between low levels of SWB and fewer remaining teeth with good self-rated mastication, which may suggest an appropriate restoration of masticatory function using some form of prosthesis, would not be confirmed.
2. Materials and methods
2.1. Ethical approval
All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and the Declaration of Helsinki (1964) and its later amendments or comparable ethical standards. The ethics committee of Yamagata University approved the study protocol (2022-106).
2.2. Study design and participants
This study was performed as part of an ongoing molecular epidemiological study utilizing the Regional Characteristics of the 21st Century Centers of Excellence Program in Japan. This study was community-based and included a baseline survey using a self-administered questionnaire. The general population aged between 40 and 79 years dwelling in the Yamagata prefecture, Japan, was the target population. A postal self-administered questionnaire survey was conducted from 2017 to 2021 among 8783 individuals from the Yamagata prefecture. The questionnaires were completed by 7447 individuals (2558 men, 4889 women; response rate: 84.8%); however, 601 were excluded due to incomplete data on the number of teeth, self-rated mastication, or SWB. A total of 6846 participants (2332 men, 4514 women) were included in the final statistical analysis.
2.3. Measurements
The self-reported questionnaire contained a survey on lifestyle, medical history, oral health, and dietary intake. SWB was assessed using a single-item question: “How happy are you?” and 4 possible answers were provided: very happy, happy, neutral, and unhappy. The number of remaining teeth and self-rated mastication were also assessed via single-item questions, respectively: “How many teeth do you have? (Restored teeth and post crown are counted but dental implants are not),” and “Can you bite tightly on both sides with your teeth or prostheses?” Regarding self-rated mastication, 3 possible answers were provided: can bite tightly on both sides, can bite tightly on 1 side, and can bite tightly on neither side. The answers to the questions on number of teeth and self-rated mastication were combined and the participants were classified into 4 groups: having ≥ 20 teeth and can bite tightly on both sides, having ≥ 20 teeth and cannot bite tightly on both sides, having < 20 teeth and can bite tightly on both sides, and having < 20 teeth and cannot bite tightly on both sides.
Additional covariates, other than the number of teeth and self-rated mastication, were derived from a similar previous study which investigated the risk factors for low levels of SWB. That study had the largest sample size in Japan and was reported in 2022.[20] The additional covariates were sex, age, marital status, educational status, self-rated health status, household income, and feelings of depression. Regarding marital status, 6 possible answers were provided: married, never married, divorced, separated, widowed, and others. Three possible answers were provided regarding educational status: university graduate or above, high school/junior college/professional training college/dropped out of university, and junior high school graduate. Self-rated health was assessed using the single-item question: “On the whole, how would you rate your general health in this last month?” with 5 possible answers; namely, excellent, very good, good, fair, and poor. Six possible answers were provided to describe the household income: > 15 million yen, 12 to 15 million yen, 9 to 12 million yen, 6 to 9 million yen, 3 to 6 million yen, and < 3 million yen. To assess mental health, we asked about the frequency of feelings of depression in the last week, and 4 possible answers were provided: never, occasionally, often, and always.
2.4. Statistical analyses
The distribution of characteristics was analyzed using the chi-squared test and the Kruskal–Wallis test for quantitative and qualitative variables. To determine the association between SWB and several variables, an ordinal logistic regression model was used. First, crude odds ratios and 95% confidence intervals for the risk of low levels of SWB (categorized as very happy, happy, neutral, and unhappy) were calculated. Second, adjusted odds ratios and 95% confidence intervals were calculated by the multivariate ordinal logistic regression analysis using the significant variables from the univariate analysis (P < .05). Statistical significance was set at P < .05. All statistical analyses were performed using SPSS version 25.0 (IBM Corp., Armonk, NY).
3. Results
Table 1 shows the distribution of the characteristics of the participants according to the groups based on SWB (very happy, happy, neutral, and unhappy). A significant distribution between each group was found for the following parameters: the combination of the number of remaining teeth and self-rated mastication, sex, marital status, self-rated health, household income, and feelings of depression.
Table 1.
Participant characteristics.
| Variable | SWB | P value† | ||||
|---|---|---|---|---|---|---|
| Very happy | Happy | Neutral | Unhappy | |||
| Number of remaining teeth and self-rated mastication, N (%) | ||||||
| ≥20 and can bite tightly bilaterally | 844 (72.7) | 2978 (68.1) | 756 (61.6) | 51 (60.0) | <.001 | * |
| ≥20 and cannot bite tightly bilaterally | 96 (8.3) | 425 (9.7) | 149 (12.1) | 15 (17.6) | ||
| <20 and can bite tightly bilaterally | 167 (14.4) | 682 (15.6) | 205 (16.7) | 13 (15.3) | ||
| <20 and cannot bite tightly bilaterally | 54 (4.7) | 288 (6.6) | 117 (9.5) | 6 (7.1) | ||
| Sex, N (%) | ||||||
| Male | 353 (30.0) | 1474 (33.7) | 466 (38.0) | 39 (45.9) | <.001 | * |
| Female | 808 (70.0) | 2899 (66.3) | 761 (62.0) | 46 (54.1) | ||
| Age, median (lowest, highest), yr | 69 (40, 75) | 68 (46,76) | 68 (42,76) | 67 (46,75) | .250 | |
| Marital status, N (%) | ||||||
| Married | 1001 (87.0) | 3680 (84.9) | 877 (72.2) | 39 (46.4) | <.001 | * |
| Never married | 24 (2.1) | 138 (3.2) | 114 (9.4) | 21 (25.0) | ||
| Divorced | 33 (2.9) | 133 (3.1) | 66 (5.4) | 9 (10.7) | ||
| Separated | 3 (0.3) | 18 (0.4) | 13 (1.1) | 2 (2.4) | ||
| Widowed | 83 (7.2) | 354 (8.2) | 140 (11.5) | 13 (15.5) | ||
| Other | 7 (0.6) | 12 (0.3) | 4 (0.3) | 0 (0.0) | ||
| Educational status, N (%) | ||||||
| University graduate or above | 132 (11.5) | 458 (10.6) | 105 (8.7) | 9 (10.6) | .200 | |
| High school/junior college/professional training college/dropped out of university | 915 (79.5) | 3474 (80.1) | 972 (80.3) | 70 (82.4) | ||
| Junior high school graduate. | 104 (9.0) | 407 (9.4) | 133 (11.0) | 6 (7.1) | ||
| Self-rated health, N (%) | ||||||
| Excellent | 187 (16.2) | 183 (4.2) | 19 (1.6) | 2 (2.4) | <.001 | * |
| Very good | 264 (22.9) | 900 (20.8) | 181 (14.9) | 8 (9.6) | ||
| Good | 588 (51.0) | 2654 (61.3) | 672 (55.4) | 29 (34.9) | ||
| Fair | 94 (8.2) | 550 (12.7) | 314 (25.9) | 33 (39.8) | ||
| Poor | 19 (1.6) | 44 (1.0) | 28 (2.3) | 11 (13.3) | ||
| Household income, N (%) | ||||||
| >1500 million yen | 30 (2.8) | 53 (1.3) | 8 (0.7) | 0 (0.0) | <.001 | * |
| 1200–1500 million yen | 24 (2.2) | 79 (1.9) | 7 (0.6) | 0 (0.0) | ||
| 900–1200 million yen | 72 (6.6) | 185 (4.5) | 33 (2.9) | 2 (2.5) | ||
| 600–900 million yen | 162 (14.9) | 512 (12.6) | 86 (7.6) | 4 (5.0) | ||
| 300–600 million yen | 432 (39.8) | 1599 (39.3) | 380 (33.4) | 18 (22.5) | ||
| <300 million yen | 366 (33.7) | 1642 (40.3) | 625 (54.9) | 56 (70.0) | ||
| Feelings of depression, N (%) | ||||||
| Never | 914 (80.5) | 2793 (65.8) | 445 (37.5) | 9 (10.8) | <.001 | * |
| Occasionally | 201 (17.7) | 1304 (30.7) | 550 (46.3) | 25 (30.1) | ||
| Often | 19 (1.7) | 111 (2.6) | 144 (12.1) | 24 (28.9) | ||
| Always | 1 (0.1) | 35 (0.8) | 48 (4.0) | 25 (30.1) | ||
SWB = subjective well-being.
Statistically significant (P<.05).
P value based on the chi-squared test or Kruskal–Wallis Test.
Table 2 shows the significant variables in the univariate and multivariate ordinal logistic regression analysis of the risk of poor SWB. All the parameters, namely, the combinations of teeth numbers and self-rated mastication, sex, age, marital status, educational status, self-rated health, household income, and feelings of depression were found to be significant. Statistical significance was observed for all parameters, except for age, in the multivariate logistic regression analysis. Specifically, individuals who had < 20 teeth and could not bite tightly on both sides (i.e., had poor mastication ability) had a 1.300-fold risk for low levels of SWB compared with individuals who had ≥ 20 teeth and could bite tightly on both sides (i.e., had good mastication ability). Women were at lower risk of low levels of SWB than men. Compared with married individuals, individuals who had never married had a 3.732-fold risk of poor self-rated happiness. Divorced, separated, and widowed status were also risk factors for low levels of SWB. Moderate educational status, meaning graduation from high school, junior college, or professional training college, or dropping out of university, were risk factors for a low level of SWB compared with high educational status, meaning a university graduate degree or above. Compared with individuals who rated their health as “excellent,” those who rated it as “very good,” “good,” “fair,” or “poor” had a significant risk of low levels of SWB. A household income of < 3 million yen or 3 to 6 million yen was a significant risk factor for low levels of SWB, compared with an income > 15 million yen. The frequencies of feelings of depression in the previous week rated as “occasionally,” “often,” and “always” were risk factors compared with a frequency of “never.”
Table 2.
Crude and adjusted odds ratios and 95% confidence intervals of the variables associated with poor SWB.
| Poor SWB (very happy, happy, neutral, and unhappy) | ||||||
|---|---|---|---|---|---|---|
| Crude OR (95% CI) | P value | Adjusted OR (95% CI)† | P value | |||
| Teeth numbers and sefl-rated mastication | ||||||
| ≥20 and can bite tightly bilaterally | 1 | 1 | ||||
| ≥20 and cannot bite tightly bilaterally | 1.451 (1.232–1.706) | <.001 | * | 1.181 (0.986–1.412) | .071 | |
| < 20 and can bite tightly bilaterally | 1.208 (1.054–1.383) | .006 | * | 1.114 (0.952–1.303) | .176 | |
| < 20 and cannot bite tightly bilaterally | 1.687 (1.392–2.044) | <.001 | * | 1.300 (1.043–1.621) | .020 | * |
| Sex | ||||||
| Male | 1 | 1 | ||||
| Female | 0.799 (0.721–0.884) | <.001 | * | 0.628 (0.557–0.707) | <.001 | * |
| Age | 0.993 (0.986–1.000) | .049 | * | 1.002 (0.994–1.011) | .583 | |
| Marital status | ||||||
| Married | 1 | 1 | ||||
| Never married | 4.092 (3.258–5.145) | <.001 | * | 3.732 (2.878–4.845) | <.001 | * |
| Divorced | 2.002 (1.545–2.593) | <.001 | * | 1.530 (1.145–2.044) | .004 | * |
| Separation | 3.469 (1.837–6.547) | <.001 | * | 2.627 (1.327–5.197) | .006 | * |
| Widowed | 1.610 (1.354–1.912) | <.001 | * | 1.557 (1.276–1.900) | <.001 | * |
| Other | 0.651 (0.284–1.487) | .308 | 0.573 (0.236–1.392) | .219 | ||
| Educational status | ||||||
| University graduate or above | 1 | 1 | ||||
| High school/junior college/professional training college/dropped out of university | 1.178 (1.004–1.381) | .044 | * | 1.332 (1.120–1.586) | .001 | * |
| Junior high school graduate. | 1.302 (1.048–1.616) | .017 | * | 1.185 (0.925–1.520) | .179 | |
| Self-rated health | ||||||
| Excellent | 1 | 1 | ||||
| Very good | 3.615 (2.886–4.527) | <.001 | * | 3.529 (2.759–4.513) | <.001 | * |
| Good | 4.860 (3.947–5.983) | <.001 | * | 4.879 (3.881–6.135) | <.001 | * |
| Fair | 11.078 (8.732–14.055) | <.001 | * | 6.482 (4.973–8.457) | <.001 | * |
| Poor | 10.751 (6.959–16.610) | <.001 | * | 6.580 (4.043–10.708) | <.001 | * |
| Household income (million yen) | ||||||
| >15 | 1 | . | 1 | |||
| 12–15 | 1.384 (0.795–2.411) | .251 | 1.344 (0.740–2.442) | .332 | ||
| 9–12 | 1.481 (0.927–2.370) | .100 | 1.314 (0.795–2.171) | .287 | ||
| 6–9 | 1.664 (1.079–2.563) | .021 | * | 1.553 (0.976–2.469) | .063 | |
| 3–6 | 2.177 (1.436–3.300) | <.001 | * | 1.898 (1.213–2.971) | .005 | * |
| <3 | 3.456 (2.280–5.238) | <.001 | * | 2.754 (1.756–4.319) | <.001 | * |
| Feelings of depression | ||||||
| Never | 1 | 1 | . | |||
| Occasionally | 2.889 (2.578–3.238) | <.001 | * | 2.762 (2.435–3.133) | <.001 | * |
| Often | 10.064 (7.949–12.756) | <.001 | * | 10.528 (8.117–13.654) | <.001 | * |
| Always | 25.254 (16.962–37.637) | <.001 | * | 22.021 (14.368–33.717) | <.001 | * |
CI = confidence interval, OR = odds ratio, SWB = subjective well-being.
Statistically significant (P <.05).
Adjusted for representative variables that were significant in univariate analysis (P <.05).
4. Discussion
In this study, we comprehensively surveyed the risk factors for low levels of SWB among Japanese individuals aged between 40 and 79 years, which revealed that individuals with < 20 teeth and poor mastication were at significant risk for low levels of SWB compared with individuals who had ≥ 20 teeth and good mastication. Furthermore, in individuals with good mastication, there were no differences between the individuals who had ≥ 20 teeth and those with < 20 teeth. Hence, insufficient mastication ability with < 20 teeth appears to result in low levels of SWB. In contrast, sufficient mastication ability seems to contribute positively to SWB, even if the number of remaining teeth is < 20. Dietary habits are well-known contributing factors to SWB.[14,16,17] Sufficient mastication ability can expand the range of food types that a person can ingest; insufficient mastication ability reduces the range of food types. It is understandable that the ability to eat various foods leads to high levels of SWB, and that not being able to eat various foods leads to low levels of SWB. Considering these factors, our results are reasonable.
In a previous study, Abbas et al[20] surveyed the risk factors for low levels of SWB in 178,090 older people in Japan and revealed that having a larger number of teeth and using a dental prosthesis were independently associated with high levels of SWB. To the best of our knowledge, the study had the largest sample size reported in the literature in Japan, and is considered one of the most reliable studies surveying the risk factors of SWB. Therefore, we used the same covariates, namely, sex, age, marital status, educational attainment, self-rated health, self-rated economic situation, and geriatric depression scale. All these covariates were found to be significant factors contributing to SWB in the previous study by Abbas et al[20] These covariates were also used in other studies to investigate the contributors to SWB.[12–14,19] In our study, the results using all the covariates were similar and significant. Accordingly, our results should be considered reasonable, despite the small sample size of our study, which was approximately 1 to 30th of the previous study.[20]
As mentioned above, the design of this study is similar to that of a previous study[20] in terms of the concept and covariates used. However, the fundamental difference is that we did not survey the combination of the remaining number of teeth and prosthesis use but surveyed the combination of the remaining number of teeth and self-rated mastication. Although prosthesis use should mean good mastication ability, most dental clinicians are aware that cases of prosthesis incompatibility do occur. Furthermore, several epidemiological studies have revealed that certain people cannot bite well despite using a prosthesis.[25–28] It is possible that the previous study only assessed whether the participants used a prosthesis or not, and there is also a possibility that the previous study could not assess mastication ability.[20] Using a prosthesis, particularly a removable prosthesis, may have both adverse and beneficial aesthetic effects. Moreover, it takes time and effort to handle removable prostheses. Other than the beneficial effects, such as good mastication ability, the disadvantages of a prosthesis cannot be ignored. If poor mastication ability is assumed to be a risk factor for low levels of SWB, it is necessary to ask patients: “Can you bite tightly on both sides with your teeth or prosthesis?” and not just “Do you use a prosthesis?” Of course, a prosthesis, even if removable, has another advantage; it notably contributes to improved esthetics and pronunciation. Because SWB refers to the overall satisfaction with life,[1,29,30] satisfaction with esthetics and pronunciation by using a prosthesis may contribute to better SWB. However, if researchers form a hypothesis that masticatory function may contribute to SWB, they should confirm not only whether a prosthesis is used but also whether mastication ability is maintained or improved. Considering these factors, combining the number of remaining teeth and self-rated mastication in the questionnaire is meaningful. To the best of our knowledge, no study has surveyed the association between SWB and the combination of the number of remaining teeth and self-rated mastication; these are the strengths of this study.
Previous studies examined the association between oral condition and SWB, revealing a positive correlation between better oral conditions and higher SWB.[20–24] Our study also examined the association between oral conditions and SWB; however, it is important to note that the target age group is an important difference between our study and the existing literature. The target population in previous reports were adolescents or relatively older people, such as those aged over 65 years. To our knowledge, our study is the first study to survey the associations between oral conditions and SWB in the general population with a wide age range, between 40 and 79 years. Furthermore, with the exception of 1 report,[20] most previous studies had a relatively small sample size, ranging between 479 and 1134 participants.[21–24] These factors should be recognized as the strengths of our study.
Our study had some limitations. First, our assessment of SWB was performed using a single-item question: “How happy are you?” Steptoe highlighted the difficulty of assessing SWB using single-item questions.[3] The variable measured by the question on SWB in our study has not been examined for reliability and validity. To assess the details of SWB, several methods, such as the Subjective Well-Being Inventory, have been reported.[31–33] The use of these methods for SWB assessment may be important in future research. Second, clinical examinations were not conducted to confirm the number of teeth and masticatory function in the present study. Only 2 questionnaires were used to assess the number of teeth and masticatory function. However, the accuracy of the correlation between the number of teeth and masticatory function by clinical examination and self-reported number of teeth and masticatory function has already been validated.[34,35] Thus, our methodology to confirm the number of teeth and masticatory function using questionnaires may not have had a significant effect on this result. Third, our questionnaire did not confirm whether removable or nonremovable prostheses were used. Individuals who had < 20 teeth but could bite on both sides should have used an appropriate prosthesis. Unlikely as it may seem, some participants might have felt that they had good mastication on both sides, even if they did not have occlusal support areas. Questionnaires on the number of teeth, self-mastication, and the use of prostheses, especially removable prostheses, should be included in questionnaires in the future. The 4th limitation is regarding the number of covariates. Although we considered a sufficient number of variables that influence SWB based on previous studies, further potential variables explaining the SWB may exist.
5. Conclusion
This study revealed, for the first time, that individuals who have < 20 teeth and poor bilateral mastication ability have a greater risk for low levels of SWB than individuals who have ≥ 20 teeth and good bilateral mastication ability. Furthermore, the study also revealed that there were no differences between individuals who had ≥ 20 teeth and good bilateral mastication activity and individuals who had < 20 teeth and good bilateral mastication ability. Having ≥ 20 teeth and good bilateral mastication ability is not only important for high levels of SWB but also to restore mastication ability in some way, for example, by using a prosthesis, when the number of remaining teeth is < 20.
Acknowledgments
We thank the Editage for editing a draft of this manuscript.
Author contributions
Conceptualization: Shigeo Ishikawa, Tsuneo Konta, Mitsuyoshi Iino.
Formal analysis: Shigeo Ishikawa, Tsuneo Konta, Shinji Susa, Kenichi Ishizawa, Naohiko Makino.
Investigation: Shigeo Ishikawa, Kenichi Ishizawa, Naohiko Makino.
Methodology: Shigeo Ishikawa, Tsuneo Konta.
Project administration: Tsuneo Konta, Yoshiyuki Ueno.
Supervision: Shinji Susa, Kenichi Ishizawa, Naohiko Makino, Yoshiyuki Ueno.
Writing – original draft: Shigeo Ishikawa.
Writing – review & editing: Shigeo Ishikawa, Tsuneo Konta, Shinji Susa, Kenichi Ishizawa, Naohiko Makino, Yoshiyuki Ueno, Naoki Okuyama, Mitsuyoshi Iino.
Abbreviation:
- SWB
- subjective well-being
The data that support the findings of this study are available from a third party, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are available from the authors upon reasonable request and with permission of the third party.
This work was supported by a grant-in-aid from the 21st Century Center of Excellence (COE) and the Global COE Program of the Japan Society for the Promotion of Science.
The authors have no conflicts of interest to disclose.
How to cite this article: Ishikawa S, Konta T, Susa S, Ishizawa K, Makino N, Ueno Y, Okuyama N, Iino M. Associations between subjective well-being, number of teeth, and self-rated mastication in Japanese adults: A cross-sectional study. Medicine 2023;102:48(e36354).
Contributor Information
Tsuneo Konta, Email: kkonta@med.id.yamagata-u.ac.jp.
Shinji Susa, Email: susa@med.id.yamagata-u.ac.jp.
Kenichi Ishizawa, Email: kishizaw@med.id.yamagata-u.ac.jp.
Naohiko Makino, Email: namakino@med.id.yamagata-u.ac.jp.
Yoshiyuki Ueno, Email: y-ueno@med.id.yamagata-u.ac.jp.
Naoki Okuyama, Email: nammzaemon@gmail.com.
Mitsuyoshi Iino, Email: m-iino@med.id.yamagata-u.ac.jp.
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