SELF-REPORTED ORAL DISEASES AND THEIR ASSOCIATION WITH THE FRAILTY INDEX AMONG OLDER JAPANESE PEOPLE: FOURYEAR FOLLOW-UP

 

R.C. Castrejón-Pérez¹, S.A. Borges-Yáñez², R. Ramírez-Aldana^1,5,6, I. Nasu³, Y. Saito⁴

 

1. Instituto Nacional de Geriatría, National Institutes of Health, Ministry of Health, Mexico; 2. Postgraduate and Research Studies Division, Dentistry School, National Autonomous University of Mexico, Mexico; 3. School of Dentistry, Matsudo Nihon University, Chiba, Japan; 4. College of Economics, Nihon University, Tokyo, Japan; 5. Escuela Superior de Ingeniería y Tecnología, Universidad Internacional de la Rioja, España; 6. Departamento de Matemáticas, Facultad de Ciencias, Universidad Nacional Autónoma de México

Corresponding Author: Roberto Carlos Castrejón-Pérez, PhD, Instituto Nacional de Geriatría, National Institutes of Health, Ministry of Health, Mexico, rcastrejon@inger.gob.mx, rc.castrejon.perez@gmail.com

J Frailty Aging 2024;in press
Published online January 31, 2024, http://dx.doi.org/10.14283/jfa.2024.10

 

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Abstract

BACKGROUND: Oral health is a relevant component for overall health. Oral disease onset at an early age and may harm several health dimensions, especially among older people, and has been associated with frailty.
OBJECTIVE: To evaluate associations between the Frailty Index (FI) and self-reported oral diseases among older, community-dwelling Japanese people.
DESIGN: Cross-sectional and prospective analyses were performed.
SETTING AND PARTICIPANTS: We analyzed data from 2,529 participants at the baseline and four-year follow-up of the Nihon University Japanese Longitudinal Study of Aging, which had a four-year follow-up.
MEASUREMENTS: We used the self-reported number of teeth, self-reported satisfaction with dentures, and self-reported ability to chew hard food as independent variables. We computed an FI that included 40 deficits as the dependent variable. The FI score ranged from 0 to 1, with a higher score associated with adverse health outcomes and mortality. Considering a gamma distribution and controlling for age, gender, marital status, education, working status, and residence area, we fitted generalized linear models.
RESULTS: We found that dissatisfied denture users had a 2.1% (95% CI 1.006–3.279) higher frailty score than non-denture users at the baseline and a 2.1% (95% CI 0.629–3.690) higher frailty score than non-denture users at the four-year follow-up. In the cross-sectional analysis, with each additional reported tooth at the baseline, the FI score was lower by 1.5% (95% CI -2.878 to -0.208) at the four-year follow-up. In both the cross-sectional and the prospective analyses, the FI scores increased as the ability to chew hard food decreased.
CONCLUSIONS: Self-reported oral diseases are associated with the FI score cross-sectionally and prospectively. Identifying factors prospectively associated with frailty may improve strategies for the next generation of older people. Considering oral diseases may help clinicians personalize treatment plans for older people.

Key words: Frailty index, number of teeth, ability to chew, satisfaction with dentures, cohort study.

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Introduction

The World Health Organization recognized oral health as a relevant component of overall health in the Global Oral Health Status Report 2022 (1). The onset of oral diseases occurs early in life, and their impact accumulates over one’s lifetime, becoming more severe in middle and older age (1, 2). Oral diseases share some risk factors with noncommunicable diseases (1-5) and impact additional domains of health and living (1, 5–9). Available evidence indicates that oral diseases are associated with changes in food selection and poor nutritional status (9–11) and with poor quality of life (12, 13). Other studies have reported that oral diseases are associated with higher mortality rates among older people (7, 8).
Frailty, recognized as a public health challenge (14, 15), is a state of increased vulnerability to outer and inner stressors due to a diminished physiological response. Frail individuals are prone to adverse health outcomes (14, 16, 17). The number of studies reporting an association between oral diseases and frailty has increased in recent years (18–27). The results of these studies support a functional path linking oral diseases and frailty (28), since the most common oral diseases associated with frailty may also harm oral function (e.g., number of natural teeth, periodontal status, occlusal force, reduced ability to chew hard food, tongue pressure, diadochokinesis, swallowing difficulties, reporting dry mouth, prosthetic characteristics, and dental decay) (18, 25, 26, 29, 30), therefore compromising nutritional status from earlier ages and for an extended period of life.
Although the association between oral diseases and frailty has been reported in different populations (20, 21, 24, 26, 31–33), most of these studies included objectively measured oral diseases, making data collection challenging and expensive due to the clinical training and standardized procedures required for accurate and valid data collection. Moreover, most prospective studies included regionally representative participants or relatively short follow-up periods (31, 33–35). This study aimed to evaluate the association between three self-reported oral diseases and the Frailty Index (FI) at baseline and at the four-year follow-up among older Japanese people.

 

Methods

This study included cross-sectional and prospective analyses of nationally representative older people participating in the Nihon University Japanese Longitudinal Study of Aging (36, 37). The sample was selected using a multistage stratified sampling method. The participants were selected from the National Registry List, the eligible voter list, and the list of housing units developed by Central Research Services Incorporated. Potential participants were 65 and over; those 75 years and over were oversampled (38). The participants were interviewed at the baseline (in 1999), in the second wave in 2001, and in the third wave in 2003. We included 2,529 participants who were interviewed at the baseline and in the third wave and had no missing values in any variable considered for the analyses.

Variables

The self-reported number of natural teeth (number of teeth; range 0–32) was measured by asking “How many original teeth do you have?” Utilization of and satisfaction with dentures were assessed by asking, “Do you have dentures? (no/yes).” Those who responded “no” were considered “non-denture users.” Those who answered “yes” were asked, “Are you satisfied with your dentures?” (no/yes). Those who responded “yes” were considered “satisfied denture users.” Those who answered “no” were considered “dissatisfied denture users.” The ability to chew hard food was measured using the question “What is the hardest group of food you are able to bite and chew?” The offered responses included an ordered list of six groups of food ranging from the most challenging (hardest) to the softest (Group 1: hard dried squid or pickled radish; Group 2: boiled pork meat or raw carrots or celery; Group 3: deep-fried tofu, pickled octopus, pickled Chinese cabbage, or raisins; Group 4: rice, apples, fish cake, or boiled asparagus; Group 5: bananas, boiled beans, canned corned beef, or wafers; Group 6unable to chew the food listed in Group 5).
The FI was the dependent variable, computed using 40 components, including symptoms, signs, disabilities, and diseases, as suggested by Searle and colleagues (39). To calculate the FI, each item was categorized as 0 if the deficit was absent and 1 if the deficit was present. The variables with ordinal scales of three options were coded with 0 if the deficit was absent, 0.5 if the deficit was partially present, and 1 if the deficit was present. Self-rated health with an ordinal response of five options was coded as 0, 0.25, 0.5, 0.75, and 1 (Supplementary Table A). The values of all responses were summed and divided by 40 to obtain a FI score ranging from 0 to 1 with a gamma distribution (39), with a higher score associated with adverse health outcomes and mortality (40).
Age (65 years old and over), sex (male or female), marital status (married, single or divorced, or widowed), educational background (completed Grade 9, completed Grade 12, or completed junior college or higher), current working status (working, retired and unemployed, retired and engaged with housework, or retired and no longer doing housework), and residence area (urban or rural) were included as covariates.

Statistical analysis

We present descriptive analyses with percentages, mean values, and standard deviation, and minimum, maximum, and median values when appropriate. We fitted generalized linear models using a gamma distribution and identity link function for both the cross-sectional and prospective approaches, with each self-reported oral condition and covariate serving as an explanatory variable (univariate models). In the multivariable analyses, we fitted similar generalized linear models. We included the control variables from the univariate analyses and each separate self-reported oral condition as explanatory variables. The reason for fitting a multivariable model for each self-reported oral condition is that there is collinearity between them. Thus, we fitted four cross-sectional and four prospective multivariable models. The FI score was multiplied by 100 so that it could be interpreted as a percentage of change by the unit of change in the independent variables of interest. All analyses used Stata version 15 (StataCorp LLC, College Station, TX, USA).

 

Results

Of the 2,529 participants included in the analyses, 56.8% were women. The women were, on average, older than the men (74.8 SD 5.9 vs 73.7 SD 6.0, respectively). Almost two-thirds of the participants were married, 33.7% were widowed, and 58.3% lived in urban areas. Most women had completed Grade 9, while 14.3% of the men had completed junior college or higher. The majority (60.4%) of the men were retired and unemployed, while half of the women were retired and engaged in housework. Regarding self-reported oral diseases, the median number of teeth was higher among the men than among the women (9 and 5, respectively), a higher proportion of the men was not using dentures, and almost two-thirds of the women were satisfied denture users. Concerning the ability to chew, most participants reported being able to chew the most challenging food group, whereas 7.1% reported being able to bite and chew only the three softest food groups (Table 1).

* Group 1-Hard dried squid or pickled radish; Group 2-Boiled pork meat, raw carrots, or celery; Group 3-Deep-fried tofu, pickled octopus, tsukemono made from Chinese cabbage, or raisins; Group 4-Rice, apples, fish cake, or boiled asparagus; Group 5-Bananas, boiled beans, canned corned beef, or wafers; Group 6-Unable to chew food listed in Group 5; FI: Frailty Index; £ t-test; ¥ chi2; ** Kruskal-Wallis

 

Cross-sectional approach

The univariate analyses showed that age, being female, single or widowed, retired and unemployed, retired and engaged with housework, retired and no longer doing housework, a dissatisfied denture user, and able to chew only softer foods were associated with a higher FI score at the baseline. Conversely, having completed Grade 12, junior college, or higher, and each additional tooth reported were associated with a lower FI score at the baseline. The covariates that remained associated with higher FI scores in the multivariable analyses were age and working status (Supplementary Table B). Regarding self-reported oral diseases, being a dissatisfied denture user and able to chew food from Groups 2–6 were associated with a higher FI score at the baseline (Table 2).

** 1-Hard dried squid or pickled radish; 2-Boiled pork meat, raw carrots, or celery; 3-Deep-fried tofu, pickled octopus, tsukemono made from Chinese cabbage, or raisins; 4-Rice, apples, fish cake, or boiled asparagus; 5-Bananas, boiled beans, canned corned beef, or wafers; 6-Unable to chew food listed in 5

 

Prospective approach

The univariate analyses showed that age, being female, single, or widowed, retired and unemployed, retired, and engaged with housework, retired and no longer doing housework, satisfied and dissatisfied denture users, and able to chew only softer foods at the baseline were associated with a higher FI score at the follow-up. We must highlight that having completed Grade 12, junior college, or higher (compared with those having completed Grade 9) and each additional tooth reported were associated with a lower FI score at the follow-up. The covariates that remained associated with higher FI scores at the follow-up in the multivariable analyses were age, being single, and working status (Supplementary Table C). Regarding self-reported oral diseases, being a dissatisfied denture user and able to chew food from Groups 2–6 were associated with a higher FI score at the follow-up. Each additional tooth reported was associated with a 1.5% lower FI score at the follow-up (Table 3).

*Covariates included in each model: Age, marital status, education background, and working status. ** 1-Hard dried squid or pickled radish; 2-Boiled pork meat, raw carrots, or celery; 3-Deep-fried tofu, pickled octopus, tsukemono made from Chinese cabbage, or raisins; 4-Rice, apples, fish cake, or boiled asparagus; 5-Bananas, boiled beans, canned corned beef, or wafers; 6-Unable to chew food listed in 5

 

Discussion

This study aimed to evaluate the associations between three self-reported oral diseases (number of teeth, utilization of and satisfaction with dentures, and ability to chew hard food) with the FI at the baseline and four years later among a sample of older Japanese people. We observed that each natural tooth reported at the baseline was associated with a lower FI score four years later. Being a dissatisfied denture user and having a reduced ability to chew hard food at the baseline were associated with a higher FI score at the baseline and an increased FI score four years later. These results suggest that the FI score of dissatisfied denture users and those with a reduced ability to chew increases over the years, while the increment in the FI score over time is lower for each additional natural tooth preserved.
The subjective nature of the oral diseases used in this manuscript could be a limitation of this study. Nevertheless, our results on the self-reported number of teeth and the ability to chew hard food are similar to those of studies of older Mexican and Chinese people, showing that a higher number of teeth was associated with a reduced incidence of frailty (19, 33). Our results are also consistent with a study of older Japanese people showing that a higher occlusal force and better chewing ability were associated with a lower incidence of frailty (31, 34, 35). These studies used objective oral measurements with a two- to five-year follow-up and measured frailty with the frailty phenotype. To the best of our knowledge, there is no previous study regarding self-reported utilization and satisfaction with dentures; nonetheless, this variable is similar to self-reported chewing ability, which has been previously associated with a higher incidence of frailty (35). Another study limitation is the data collection timeframe (1999–2003). However, since our results align with those of studies gathering “more recent” data, the external validity of our results is assumed.
An additional limitation related to the self-reported nature of the variables in our study is that we could not include any measurements of periodontal diseases. Despite the sound theoretical bases suggesting an association between periodontitis and frailty (41–43), few studies have reported an association between periodontal status and frailty cross-sectionally and prospectively (21, 23, 28, 33). Some studies have identified an association between periodontal disease and chronic diseases (44, 45) that are also associated with frailty (46–49); therefore, an association between periodontal status and frailty is expected (42). However, the scarce evidence on this association points to the need for additional research using currently accepted criteria for periodontal and frailty measurements and classifications for appropriate interpretation.
Our study reported a consistent association between self-reported oral diseases and frailty. This suggests that these subjective variables can be included in questionnaires used in future studies on this topic. Further investigations could use larger samples to confirm our findings and identify additional associations. The results of our self-reported independent variables may also indicate the relevance of early interventions, since the onset of these oral diseases occurs early in life, with individuals reporting no recognizable eating limitations (i.e., chewing or swallowing) as symptoms. Individuals with these oral diseases may change the components of their diet, replacing essential nutrients with something more comfortably chewed and swallowed but lower in nutritional content (Figure 2). Other studies have confirmed this (9, 27, 50–54).

 

It is important to note that one study has reported an interaction between the number of teeth and diabetes (33). This finding reflects the challenge of any approach to research on older people who, over time, accumulate various health experiences that may interact with each other (17, 55–57). This is part of the rationale for developing the FI and the concept of frailty (16, 17, 55, 57, 58). Several indices claim to measure frailty (16, 55, 57–61). The frailty phenotype derived from the Cardiovascular Health Study is the most popular, but it has been criticized because it is predominantly related to muscle strength (16, 62). Most other indices have been validated by probing predictive validity and using the frailty phenotype as a reference (14). The main advantage of the frailty phenotype is its clinical utility and ease of use. However, the FI is a more comprehensive approach because it is a single measurement that considers the accumulation of deficits over an entire lifetime and provides an appropriate overview of the whole physiological system and its complexity (14, 17, 39, 56, 57, 61, 62).
Several advantages exist for prospectively identifying factors associated with frailty. Clinicians may consider these relevant factors when designing personalized treatment plans for older people. Health economists may consider the impact of oral diseases on older people’s treatment costs at the familial, institutional, and governmental levels. Our results suggest that preventive oral care could be essential for community health interventions. Similar analyses, including mortality data, could investigate whether oral diseases (objectively or subjectively measured) are related to mortality and frailty. It would also be worthwhile to examine whether improving the chewing ability of adults via dental interventions could help reduce the incidence and prevalence of frailty later in life.

 

Conclusion

This study shows that being a dissatisfied denture user and unable to chew hard food are associated with higher FI scores cross-sectionally and prospectively after controlling for relevant covariates. Each additional tooth is prospectively associated with a lower FI score after controlling for covariates. Our findings demonstrate that measuring self-reported oral diseases is suitable for identifying cross-sectional and prospective associations between oral health and frailty. Our results also suggest the importance of preserving oral health (i.e., preventing tooth loss, maintaining the ability to chew, and improving satisfaction with dentures) during youth and adulthood to reduce the risk of adverse health outcomes later in life.

 

Acknowledgments: The authors thank Luis Miguel Gutiérrez Robledo, Carmen García-Peña, and Nihon University for supporting this manuscript.

Conflict of interest: The authors declare no conflicts of interest relevant to this manuscript.

Authors’ contributions: All authors meet the criteria for authorship stated in the Uniform Requirements for Manuscripts Submitted to Biomedical Journals. YS participated in the design and data collection of the study and the analysis and discussion of the results. IN was involved in the design and data collection of the study and discussion of the results. RAR participated in the design of the analyses and interpretation of the data. SABY contributed to the interpretation and discussion of the results. RCCP was involved in the design of the data analyses and discussion of the results.

Funding: Nihon University funded the Nihon University Japanese Longitudinal Study on Aging. The study was initiated with support from the Population Research Institute, Nihon University, while the first author of this article was a visiting research fellow at the Institute.

Ethical standards: The study followed the ethical standards in accordance with the Ethics Committee from the Nihon University and following the Helsinki declaration of 1975.

 

SUPPLEMENTARY MATERIAL

 

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