INTRODUCTION
Japan is becoming an unprecedented “super-aged society,” with the population aged 65 years and older reaching 36.25 million as of September 2024. The proportion of older adults now stands at 29.3% and is projected to increase to 33.3% by 2037, indicating that approximately one in every three people in Japan will be 65 or older.1,2)
Therefore, maintaining the health of older adults and preventing their progression to a state requiring long-term care have become urgent social issues. A key focus of this effort is the prevention and management of frailty, which often precedes the need for long-term care. Frailty is a multidimensional condition involving physical, psychological, and social decline and is associated with a high risk of health deterioration and mortality.3) However, it is deemed reversible with the implementation of proper preventive and therapeutic interventions, delaying dependency and restoring health.
Malnutrition is also a major contributor to frailty. Maintaining oral function is essential for preventing malnutrition in older adults,4) and a decline in oral function is closely associated with the onset of frailty.5) Therefore, the early prevention and management of oral hypofunction are crucial for maintaining a healthy and independent life.6)
In response to Japan’s super-aged society, public health policy has increasingly emphasized the prevention of frailty and extension of healthy life expectancy.7) In dental care, increased attention is being paid to the evaluation and management of oral hypofunction, including measures to prevent oral frailty. While several studies have explored the relationship between nutritional status and oral function,8-10) few have explored the association between oral function and indicators such as the Dietary Variety Score (DVS) and body composition within the setting of community dental clinics.11,12)
Moreover, oral hypofunction has been reported in approximately 48% of individuals in their 50s and over 60% of those in their 60s.13) According to population estimates from 2023, people aged 50 and older account for approximately 50.6% of the total population.14) These statistics suggest that a large proportion of patients attending community dental clinics belong to this age group.
Considering these factors, community dental clinics are expected to play an important role in promoting health and preventing frailty among older adults. This highlights the need for a comprehensive evaluation of both nutritional status and oral function including integrated care.
This study aimed to explore the need for nutritional management in community dental clinics by assessing dietary variety through the DVS and examining changes in oral function and body composition among outpatients aged 50 and older who may be experiencing oral hypofunction.
MATERIALS AND METHODS
Participants
This study included 74 patients aged 50 years or older (25 males and 49 females; mean age 72.3±9.6 years) who were outpatients at a community dental clinic located in Nogata City, Fukuoka Prefecture, Japan. Participants were consecutively recruited from routine dental visits during the study period, and those who met the inclusion criteria were enrolled. Prior to enrollment, all participants provided written informed consent.
Study Design and Timing
Assessments were conducted at baseline and again 1 year later for comparative analysis.
Basic Information
Demographic information including age and sex was extracted from the participants’ electronic medical records.
Evaluation of Oral Function
Oral function was evaluated using seven parameters based on the diagnostic criteria for oral hypofunction proposed by the Japanese Society of Gerodontology.15) The following items were evaluated using standardized procedures. The following seven functional parameters were evaluated, as described below. A diagnosis of oral hypofunction was established when three or more of these functions were found to be impaired.
Tongue Coating Index
The dorsum of the tongue was visually divided into nine sections and each section was scored from 0 to 2 based on the degree of coating. The Tongue Coating Index (TCI) was calculated as a percentage of the total score. A TCI ≥50% was defined as poor oral hygiene.16)
Oral moisture
Oral mucosal moisture was measured using an oral moisture-checking device (Mucus; Life Co. Ltd., Saitama, Japan). The sensor was placed at the center of the tongue dorsum (10 mm from the tip) and pressed with a force of 200 g for 3 seconds. Measurements were repeated three times and the median value was used. Oral dryness was defined as a value <27.0.17)
Oral diadochokinesis
Tongue-lip motor function was evaluated using oral diadochokinesis (ODK) with a dedicated measuring device (Kenko-kun Handy; Takei Scientific Instruments, Niigata, Japan). The participants were asked to repeat the syllables /pa/, /ta/, and /ka/ as quickly as possible. Decreased function was defined as a repetition rate of <6.0 times per second for any syllable.20)
Tongue pressure
Maximum tongue pressure was measured using a tongue pressure meter (TPM-02; JMS Co., Ltd., Hiroshima, Japan). A balloon probe was inflated and placed on the anterior palate and the participants were instructed to press it with maximum force. Measurements were taken three times, and the highest value was used. Values <30 kPa indicate low tongue pressure.21)
Masticatory function
Masticatory performance was evaluated using a 2-g test gummy jelly and a glucose measuring device (Glucosensor GS-II; GC Corp., Tokyo, Japan). Participants chewed the jelly for 20 seconds and rinsed it with 10 mL of water. The eluent was collected and its glucose concentration was measured. Values <100 mg/dL indicate reduced masticatory function.22)
Swallowing function (EAT-10)
The swallowing ability was evaluated using the 10-item Eating Assessment Tool (EAT-10; Nestlé Nutrition Institute, Vevey, Switzerland). Each item is scored on a 5-point Likert scale ranging from 0 (no problem) to 4 (severe problem). A total score ≥3 indicated impaired swallowing function.23)
Dietary Variety
Dietary variety was assessed using the DVS.24) The DVS comprises 10 food groups commonly consumed in the Japanese diet: meat, fish/shellfish, eggs, milk, soybean products, green and yellow vegetables, potatoes, fruits, seaweed, and fats/oils. Participants were asked to report their consumption frequency for each food group over the past week. A score of 1 was assigned for items consumed almost every day (6–7 days/week), and a score of 0 was assigned otherwise. The total DVS was calculated by summing the scores for all 10 items, yielding a score ranging from 0 to 10, with higher scores indicating greater dietary variety.
Dietary intake data were collected using either a paper-based questionnaire or a mobile food recording application (Mogumogu Diary, Morinaga Milk Industry Clinico Co., Ltd., Tokyo, Japan).25)
Body Composition Measurements
Body composition, including weight, body fat percentage, and muscle mass, was assessed using a bioelectrical impedance analyzer (InBody Dial H20; InBody Japan). Height was self-reported, and body mass index was subsequently calculated.26)
Intervention
Based on the DVS results, registered dietitians or nutritionists provided individualized dietary counseling. Oral function training was guided by dental hygienists using the 2019 edition of “For Those Diagnosed with Oral Hypofunction,” tailored to the specific impaired domains. These interventions were conducted during regular follow-up visits every 3–4 months.27)
Statistical Analysis
Sex-based comparisons were established using the Mann–Whitney U test, and Wilcoxon signed-rank tests were utilized to examine longitudinal changes in body composition and oral function. McNemar’s test was employed to evaluate changes in the consumption status of each of the 10 food groups included in the DVS. Changes in total DVS scores were analyzed using Wilcoxon signed-rank tests, while changes in the prevalence of oral hypofunction were analyzed using McNemar’s exact test. All statistical analyses were conducted using EZR (Easy R version 4.3.0), with significance set at p<0.05.
RESULTS
Participant Characteristics
Of the 103 individuals who provided informed consent, those with incomplete data or for whom long-term follow-up was not feasible were excluded. The final analysis included 74 participants (25 males and 49 females) (Fig. 1). The mean age was 72.3±9.6 years (72.1±10.5 years for males and 72.4±9.1 years for females). The mean number of days between the baseline and 1-year follow-up assessments was 310.4±146.5 days. The participant characteristics are presented in Table 1.
Changes in Body Composition and Oral Function
Changes in body composition and seven oral function parameters from baseline to 1 year later are demonstrated in Table 2 and Figs. 2–3. No significant changes were noted in the body composition.
Conversely, improvements were observed in all seven oral function parameters. Specifically, oral dryness, occlusal force, masticatory function, ODK (/pa/, /ta/, /ka/), and tongue pressure improved, whereas the TCI and EAT-10 scores decreased. Among these, the improvements in TCI and tongue pressure were statistically significant. Additionally, the prevalence of oral hypofunction significantly declined.
Changes in DVS
Changes in the DVS from baseline to 1 year later are shown in Table 3 and Fig. 4. Of the 10 food groups included in the DVS, eight demonstrated a significant increase in consumption frequency: fish/shellfish, meat, eggs, milk, seaweed, potatoes, fruits, and oils/fats. The total DVS score also increased significantly.
DISCUSSION
Among outpatients aged 50 years and older who visited community dental clinics, significant improvements were noted after 1 year in both the total DVS score and the prevalence of oral hypofunction.
The use of DVS enables the assessment of dietary diversity, allowing for the evaluation of nutritional intake habits across multiple food groups.24) In this study, assessing dietary habits using the DVS likely prompted participants to reflect on their own eating patterns, which may have contributed to an increase in total DVS scores, that is, an improvement in dietary variety.
In older adults, consuming a variety of foods may contribute to better nutritional balance and improved physical function.24) Rather than focusing on individual nutrients, improving the overall quality of diet is essential for maintaining health. Compared to other nutritional assessment methods, the DVS is a useful and practical tool.27) Furthermore, previous research has shown that more severe oral frailty is associated with lower DVS scores,9) and that DVS is related to sarcopenia in older adults.28) In addition, previous studies have reported that oral function is closely associated with frailty in community-dwelling older adults.29) Therefore, the observed improvements in oral hypofunction prevalence may result from the combined effects of targeted oral function training and increased dietary diversity. Thus, in community dental clinics, assessing dietary intake using the DVS and providing nutritional guidance may improve dietary variety and oral function, contributing to the maintenance and improvement of overall health in older adults. These findings indicate a promising potential for application in future clinical dental practice.
Improvements were noted in the DVS components such as seafood, meat, eggs, milk, seaweed, potatoes, fruit, and fats/oils, including improvements in the TCI and tongue pressure. Improved tongue pressure supports better nutritional intake in older adults, especially when related to the increased consumption of animal-based proteins.30) In the present study, an increase in the intake of animal proteins (e.g., seafood, meat, eggs, and milk) and improvements in tongue pressure were noted. The participants in the tongue-cleaning group demonstrated better maintenance of tongue pressure than those in the standard oral care group.31) The results of this study indicate that nutritional guidance based on the DVS combined with tongue cleaning to address poor oral hygiene contributes to improvements in both TCI and tongue pressure, thus supporting previous findings.
However, nutrition education in dental programs is insufficient worldwide.32) A previous study reported that 47% of dental students lacked confidence in providing oral preventive care, including nutritional guidance, which may hinder effective clinical nutritional care and result in patients not receiving the care they require.32) In this study, participants received individualized nutritional guidance from registered dietitians or nutritionists based on their DVS scores, and dental hygienists provided oral function training tailored to impaired functions. Employing dietitians along with dental hygienists, who are commonly found in community dental clinics, could allow more specialized nutritional support and contribute to improved health outcomes. Particularly, interventions that emphasize the connection between dietary variety and oral function may help maintain and promote health in older adults and contribute to extending healthy life expectancy.
The study results underscore the value of a comprehensive approach that integrates nutritional management, oral function training, and oral hygiene care in supporting older adults. In light of the growing emphasis on the triad of rehabilitation, nutrition, and oral care,33,34) these findings suggest that this approach may serve as a foundational model for patient intervention in community dental clinics.
Regarding the limitations, this study was conducted at a single community dental clinic in Nogata City, Fukuoka Prefecture and included only outpatients aged 50 years and older. Therefore, generalizability to other regions or age groups may be limited. Future studies involving different populations and settings are required to confirm the reproducibility of these findings.
In this study, improvements in oral function were likely driven primarily by the oral function training provided by dental hygienists. Although previous studies have suggested that greater dietary variety may support oral health,9) our 1-year observational design was not sufficient to evaluate whether increased dietary variety directly improves oral hypofunction. Further long-term studies are warranted to clarify how dietary variety and training-induced improvements in oral function interact over time.
In conclusion, in this study, improvements in oral function achieved through targeted training by dental hygienists appeared to contribute to increased dietary variety among older adults.
These findings indicate that interventions emphasizing both nutritional management and oral function in community dental clinics may contribute to maintaining and improving the health of older adults and may play an important role in extending healthy life expectancy.
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