Association between Oral Frailty and Intrinsic Capacity among Older Patients

doi:10.21203/rs.3.rs-4919540/v1

OBJECTIVES: Oral and systemic health are interrelated and interact with each other. However, the relationship between intrinsic capacity (IC) and oral frailty (OF) has not been studied. Hence, the purpose of this research was to clarify the correlation between OF and IC in older patients.

DESIGN: Cross-sectional study.

SETTING: Hospital-based.

PARTICIPANTS: This investigation included 303 patients aged ≥60 years (149 women and 154 men).

MEASUREMENTS: IC was evaluated in five dimensions, including cognition (Mini-Mental State Examination), vitality (Short-Form Mini Nutritional Assessment), locomotion (Short Physical Performance Battery test), psychological (15-item Geriatric Depression Scale), and sensory (self-reported hearing and vision) capacities. On the basis of thefive domains, an IC composite score (0–5) was created, with lower scores denoting worse IC. The Oral Frailty Index-8 (OFI-8) is a questionnaire that can be usedto screen for oral frailty simply. Eight factors were considered to determine the OF classification. Multiple linear and logistic regressions were carried out to investigate the relationships between OF and its items with the IC composite score and IC domains.

RESULTS: A total of 303 patients were enrolled, with an average age of 75.77±8.18 years. Overall, 44.2% and 61.1% of the participants had OF and IC impairment, respectively. Multiple linear and logistic regressions revealedthat OF was an independent predictor of IC decline. Additionally, multiple linear regression analyses revealedthat the OF group had lower scores in the IC domains (vitality and locomotion) and higher scores in the psychological domain than the non-OF group. OF items (inability to chew hard food [β=-0.172, p=0.002], less frequently going out [β=-0.125, p=0.018], and brushing teeth less than twice a day [β=-0.151, p=0.004]) were the most susceptible to the impact of IC decline. Among the three OF items above, the inability to chew hard food was correlated with worse locomotion (β=-0.122, p=0.028) and psychological capacity (β=0.151, p=0.018), brushing teeth less than twice a day was related to worse cognitive (β=-0.168, p=0.006) and sensory capacity (β=-0.126, p=0.029), and less frequently going out was associated with worse locomotion function (β=-0.202, p<0.001).

CONCLUSION: The present findings suggest that patients with OF may have more severe IC deficits. Among OF items, the inability to chew hard food, brushing teeth less than twice a day, and less frequently going out are important indicators related to the development of IC decline. OF may be employed to detect and manage IC decline.

Intrinsic capacity

oral frailty

older adults

Intrinsic capacity (IC), the fundamental component of functional ability, was initially conceptualized by the World Health Organization (WHO) in the World Report on Aging and Health in 2015 as a framework for a public health response to population aging[1]. IC comprises all of the individual-level capacities that a person can draw on and comprises five critical domains: locomotion, cognition, vitality, psychology, and sensory capacity[2]. According to accumulating evidence, IC declines far sooner than age-related symptoms or diseases do, and it is susceptible to negative health consequences such as frailty, functional disability, falls, sarcopenia, hospitalization, and mortality[3–6]. Care dependency can be avoided if priority conditions linked to reductions in IC are identified and treated early on, as advised by the WHO recommendations for integrated care for older persons (ICOPE)[7]. Thus, it is essential to address IC risk factors and identify those who are at risk to promote healthy aging.

Oral frailty (OF), introduced in Japan, is an age-related phenomenon reflected in accumulated deficits in oral health along with a deterioration in cognitive and physical functions[8], which negatively impacts overall health. There have been several reports on the associations between OF and decreased IC domains, such as malnutrition, cognitive impairment, lower physical performance, and depression[9–12]. Various plausible explanations for these correlations include (i) the influence of malocclusion and mandibular lateral displacement on the body's stability and control of posture, as well as muscular performance [13, 14]; (ii) the effect of poor nutritional intake caused by masticatory and swallowing disorders on the chronic deterioration of physical and cognitive function [12, 15–18]; (iii) the increased serum levels of proinflammatory cytokines observed in periodontal and endodontic diseases on muscle metabolism and chronic systemic diseases[19, 20]; and (iv) the impact of the reduction in periodontal ligament proprioceptive input on sensory input to the brain leading to declining cognitive function[21]. Furthermore, early-stage OF is reversible. For this reason, early diagnosis and treatment of OF are particularly helpful.

However, no studies have focused on these domains together as an IC composite concept to investigate the associations of IC with OF and explore the relationships between IC and OF components. Therefore, it is imperative to analyze the relationship between integrated IC and OF, as it helps to guide the identification of potential oral deficits in older adults and provides important evidence for managing IC.

Study design and participants

This was a cross-sectional study, and participants were recruited from the Geriatric Hospital of Nanjing Medical University in China via convenience sampling. A total of 303 participants were recruited from September 2023 to April 2024, including 154 males and 149 females, with an average age of 75.77 ± 8.18 years. The inclusion criteria were as follows: (ⅰ) aged ≥ 60 years and (ⅱ) capable of independently completing the questionnaire. (ⅲ) voluntary participation in research. The exclusion criteria were as follows: (ⅰ) acute phase of oral disease or after oral surgery; (ⅱ) severe mental disorders and dementia; (ⅲ) acute or terminal stage of the disease; (ⅳ) inability to provide informed consent due to aphasia, deafness, or blindness; (ⅴ) incomplete data concerning the main variables.

Ethical approval

was obtained from the Medical Ethics Committee of the Geriatric Hospital of Nanjing Medical University (Ethics number: 2020025). All participants voluntarily participated in the study and signed an informed consent form.

IC assessment

IC was measured via 5 domains, including the cognition, locomotion, vitality, psychology and sensory domains. Each domain was scored in a 0–1 range to stratify two statuses of the function (0 = impaired; 1 = normal). Cognition was assessed via the Chinese version of the Mini-Mental State Examination (MMSE) (range = 0–30)[22]. The scores of ≤ 17 in illiterate individuals, ≤ 20 in individuals with primary school education and ≤ 24 in individuals with middle school or higher education indicating cognitive impairment were computed as “0”, otherwise “1”. Vitality was assessed via the Short-Form Mini Nutritional Assessment (MNA-SF)[23], with a score of ≤ 11 indicating vitality impairment (0 points). Locomotion was evaluated with the Short Physical Performance Battery test (SPPB) [24], which comprises a 4-meter gait speed, five times sit-to-stand test (FTSST), and static balance. SPPB scores of 0–9 points and 10–12 points were computed as “0”, and “1”, respectively. The 15-item Geriatric Depression Scale (GDS-15) was used to determine psychological capacity[25], with a score of > 8 indicating impairment (0 points). The sensory domain was evaluated via two self-administered questionnaires related to vision and hearing. “Do you have difficulty reading magazines or newspapers?” “Do you have difficulty hearing when someone speaks in a small voice?” If the patient answered “yes” to either question indicating sensory impairment (0 points). The total IC composite score ranges from 0 to 5, with a higher composite score indicating a higher IC reserve. Dysfunction in any domain of the IC is considered IC impairment. Additionally, there are no standardized criteria for grading IC, and we define a worse IC as 0–2 points (< first quartile) and a greater IC as 3–5 points (≥ first quartile).

Oral frailty assessment

The Oral Frailty Index-8 (OFI-8) developed by the Japanese Dental Association was the basis for the OF assessment[26]. The questionnaire consists of eight items. All the items were scored as follows: (ⅰ) Do you have any difficulties eating tough foods compared to 6 months ago? (Yes: 2 points). (ⅱ) Have you choked on your tea or soup recently? (Yes: 2 points). (ⅲ) Denture use (yes: 2 points). (ⅳ) Do you often experience having a dry mouth? (Yes: 1 point). (ⅴ) Do you go out less frequently than you did last year? (Yes: 1 point). (ⅵ) Can you eat hard foods like squid jerky or pickled radish? (No: 1 point). (ⅶ) How many times do you brush your teeth per day? (< 2 times/day: 1 point). (ⅷ) Do you visit a dental clinic at least annually? (No: 1 point). The total score of the 8 items was 0–3 points for non-OF and 4–11 points for OF.

Covariates

Data were collected by two experienced and trained nurses through face-to-face interviews. Age, sex, residence status (living alone or not), monthly income, marital status (married or other), education level (< 6 years, 6–12 years, or > 12 years), history of drinking and smoking (yes or no), self-reported sleep quality, habit of physical activity (yes or no), and body mass index (BMI) were investigated. Handgrip strength (HGS) was measured with an electronic hand dynamometer (EH101; Camry, Zhongshan, China). Each participant tested their handgrip strength twice with the dominant hand in a standing position and the higher value was recorded. The cutoff points for low grip strength for males and females were < 28 and < 18 kg, respectively. The appendicular skeletal muscle mass (ASM) was measured via bioelectrical impedance analysis (InBody S10, Korea), and ASMI (appendicular skeletal muscle mass/height²) values of < 7.0 kg/m² for men and < 5.7 kg/m² for women were defined as low appendicular skeletal muscle mass. Medical and medication histories were obtained through medical records and self-reports. Multimorbidity was defined as the presence of 2 or more chronic diseases in an individual[27]. Polypharmacy was defined as the concomitant use of ≥ 5 medications.

Data analysis

The data were analyzed via SPSS (version 25.0). First, we compared the demographic characteristics of IC among the participants. Categorical variables are expressed as frequencies (N) and percentages (%). The means ± standard deviations were used to characterize continuous variables that were normally distributed. The median [1st quartile, 3rd quartile] was used to describe continuous variables that did not. Because the IC scores under different categories did not conform to a normal distribution, the Mann‒Whitney U test, Kruskal‒Wallis H test, and Spearman rank correlation analysis were used. Second, multiple linear and logistic regressions were used to explore the relationships between oral frailty (including OF items [dichotomic variables]) and IC, with the IC composite score, each IC domain scores or worse IC (dichotomic variables) as the dependent variables, adjusting for potential variables in the univariate analysis. Standard errors (SE) are presented in conjunction with beta regression coefficients (β). A significance level of α = 0.05 was implemented in a bilateral test.

Characteristics of the participants

The questionnaire was distributed and collected simultaneously. As a result, every questionnaire was gathered. A total of 303 participants (mean age 75.77 ± 8.18 years [range, 60–95 years]; 154 [50.8%] men, 149 [49.3%] women) were included, with 134 (44.2%) oral frailty, 185 (61.1%) IC impairment. The basic characteristics of the participants by IC composite score are shown in Table 1. IC composite scores were lower in females than in males. The participants with higher IC composite scores were younger, married, lived with others, had better sleep quality, had higher HGS and ASMI, and were less likely to have a history of stroke, osteoporosis, comorbidities, or polypharmacy (all p < 0.05). In addition, significant differences in the IC composite score were also observed in education level, monthly income, and BMI. However, significant differences in the IC composite score were not observed in variables about lifestyle (such as smoking and drinking), physical activity habits, hypertension, hyperlipidemia, diabetes mellitus, or coronary heart disease.

Table 1

Characteristics of the older patients according to IC composite score
Variables	Total (n = 303)	IC composite score M (P25, P75)	H/Z	P-value
Age ground (%)			52.487	< 0.001
60–69 years	75(24.8)	5(4,5)
70–79 years	123(40.6)	4(4,5)
≥ 80 years	105(34.7)	3(3,4)
Gender (%)			-2.739	0.006
male	154(50.8)	4(4,5)
female	149(49.2)	4(3,5)
Education level (%)			14.242	< 0.001
≤ 6 years	14(4.6)	3.5(3,4.25)
6–12 years	86(28.4)	4(3,5)
>12 years	203(67)	4(4,5)
Marital status (%)			-2.696	0.007
married	238(78.5)	4(4,5)
others	65(21.5)	4(3,5)
Residence status (%)			-2.631	0.009
living alone	36(11.9)	4(3,4)
living with others	267(88.1)	4(3,5)
Monthly income (%)			10.431	0.005
< 5000 RMB	49(16.3)	4(3.5,5)
5000–10000 RMB	94(31.2)	4(3,5)
> 10000 RMB	158(52.5)	4(4,5)
Smoking history (%)			-0.041	0.967
yes	33(10.9)	4(3,5)
no	270(89.1)	4(3,5)
Drinking alcohol history (%)			-1.666	0.096
yes	55(18.3)	4(4,5)
no	246(81.7)	4(3,5)
Self-reported sleep quality (%)			-3.043	0.002
good	175(57.8)	4(4,5)
bad	128(42.2)	4(3,5)
Habit of physical activity (%)			-1.765	0.078
yes	107(35.3)	4(4,5)
no	196(64.7)	4(3,5)
HGS			-5.075	< 0.001
low	89(29.8)	4(2.5,4.5)
normal	210(70.2)	4(4,5)
ASMI			-4.217	< 0.001
low	80(27.4)	4(3,4)
normal	212(72.6)	4(4,5)
BMI group (%)			12.969	0.005
< 18.5 kg/m²	7(2.3)	3(1,4)
18.5–24 kg/m²	130(42.9)	4(3,5)
24–28 kg/m²	130(42.9)	4(4,5)
≥ 28 kg/m²	36(11.9)	4(3,5)
History of stroke (%)			-5.979	< 0.001
yes	82(27.1)	4(3,4)
no	221(72.9)	4(4,5)
Hypertension (%)			-0.793	0.428
yes	181(59.7)	4(3,5)
no	122(40.3)	4(4,5)
Hyperlipidemia (%)			-1.123	0.261
yes	70(23.1)	4(4,5)
no	233(76.9)	4(3,5)
Diabetes mellitus (%)			-1.051	0.293
yes	117(38.6)	4(3,5)
no	186(61.4)	4(3,5)
Coronary heart disease (%)			-1.207	0.228
yes	66(21.8)	4(3,5)
no	237(78.2)	4(3,5)
Osteoporosis (%)			-3.713	< 0.001
yes	113(37.3)	4(3,5)
no	190(62.7)	4(4,5)
Comorbidity (%)			-4.121	< 0.001
yes	244(80.5)	4(3,5)
no	59(19.5)	5(4,5)
Polypharmacy (%)			-3.211	0.001
yes	152(51.4)	4(3,5)
no	144(48.6)	4(4,5)

The data are expressed as n (%) or M (P25, P75). P values were calculated with the Mann–Whitney U test and the Kruskal‒Wallis H test. Abbreviations: IC, intrinsic capacity; M (P25, P75), median (25th/75th percentile); RMB, Ren Min Bi; HGS, handgrip strength; ASMI, appendicular skeletal muscle mass index; BMI, body mass index.

Individuals with various IC composite scores were compared in terms of their oral frailty status (Table 2). The univariate analysis results revealed significant differences in OF (p < 0.001), inability to chew hard food (p < 0.001), less frequently going out (p < 0.001), choking (p = 0.004), xerostomia (p < 0.001) and no regular visits to the dentist (p = 0.004) for older patients by IC composite score. The OF scores were negatively correlated with the IC composite scores. Additionally, Fig. 1 shows that a higher percentage of oral frailty was associated with a lower IC composite score.

Table 2

Univariate analysis between OF with its items and IC composite score
Variables	Total (n = 303)	IC composite score M (P25, P75)	Z/r	P value
OF score OF (%)			-0.312 -4.282	< 0.001 < 0.001
yes	134(44.2)	4(3,5)
no	169(55.8)	4(4,5)
OF items (%)
Inability to chew hard food			-5.639	< 0.001
yes	57(18.8)	3(2,4)
no	246(81.2)	4(4,5)
Brushing teeth less than twice a day			-1.856	0.063
yes	68(22.4)	4(3,5)
no	235(77.6)	4(3,5)
Less frequently going out			-4.121	< 0.001
yes	57(18.8)	3(3,4)
no	246(81.2)	4(4,5)
Difficulty eating tough food			-1.127	0.260
yes	21(6.9)	4(2.5,5)
no	282(93.1)	4(3,5)
Choking			-2.842	0.004
yes	67(22.1)	4(3,5)
no	236(77.9)	4(3.25,5)
Denture use			-0.880	0.379
yes	156(51.5)	4(3,5)
no	147(48.5)	4(4,5)
Xerostomia			-3.651	< 0.001
yes	126(41.6)	4(3,5)
no	177(58.4)	4(4,5)
No regular visits to the dentist			-2.885	0.004
yes	67(22.1)	5(4,5)
no	236(77.9)	4(3,5)

The data are expressed as n (%) or M (P25, P75). P values were calculated via Spearman rank correlation analysis and the Mann–Whitney U test. Abbreviations: OF, oral frailty; IC, intrinsic capacity; M (P25, P75), median (25th/75th percentile).

Relationship between OF and IC

Table 3 shows the adjusted associations between OF with its items and IC composite score for all participants. According to our multiple linear regression models, the IC composite score was negatively associated with the OF score (β=-0.174, p = 0.001), OF (β=-0.118, p = 0.024), inability to chew hard food (β=-0.172, p = 0.002), brushing teeth less than twice a day (β=-0.151, p = 0.004) and, less frequently, going out (β=-0.125, p = 0.018). However, no significant associations were detected between other OF items and the IC composite score.

Table 3

Multiple linear regression evaluating the associations of OF and its items with the IC composite score and IC domain scores
	IC composite score			Cognition domain score			Vitality domain score			Locomotion domain score			Psychological domain score			Sensory domain score
	β	SE	P	β	SE	P	β	SE	P	β	SE	P	β	SE	P	β	SE	P
OF score	-0.174	0.028	0.001	-0.111	0.077	0.075	-0.134	0.037	0.018	-0.140	0.072	0.011	0.247	0.052	<0.001	-0.018	0.014	0.764
OF (yes)	-0.118	0.112	0.024	-0.072	0.304	0.230	-0.123	0.147	0.025	-0.140	0.287	0.008	0.141	0.209	0.022	-0.012	0.057	0.831
Inability to chew hard food	-0.172	0.151	0.002	-0.106	0.411	0.092	-0.023	0.201	0.690	-0.122	0.392	0.028	0.151	0.284	0.018	-0.100	0.077	0.095
Brushing teeth < 2 times a day	-0.151	0.134	0.004	-0.168	0.361	0.006	-0.110	0.177	0.050	-0.086	0.347	0.112	0.071	0.254	0.260	-0.126	0.068	0.029
Less frequently going out	-0.125	0.148	0.018	-0.014	0.404	0.817	-0.074	0.196	0.185	-0.202	0.375	<0.001	0.026	0.281	0.684	-0.022	0.076	0.703
Difficulty eating tough food	-0.038	0.216	0.456	-0.046	0.581	0.428	-0.023	0.283	0.671	-0.039	0.552	0.448	0.220	0.391	<0.001	0.022	0.109	0.689
Choking	-0.071	0.135	0.177	-0.024	0.364	0.696	-0.048	0.177	0.386	-0.008	0.346	0.884	0.122	0.251	0.048	-0.008	0.068	0.891
Denture use	0.002	0.108	0.962	0.048	0.292	0.411	-0.030	0.142	0.579	-0.051	0.277	0.322	0.087	0.201	0.141	0.073	0.055	0.182
Xerostomia	-0.091	0.112	0.079	-0.123	0.301	0.039	-0.102	0.146	0.061	-0.020	0.288	0.707	0.104	0.209	0.090	-0.020	0.057	0.725
No regular visits to the dentist	-0.072	0.134	0.157	-0.087	0.360	0.140	-0.056	0.175	0.294	-0.024	0.346	0.651	0.044	0.249	0.466	-0.072	0.068	0.192
Abbreviations: OF, oral frailty; IC, intrinsic capacity; β, beta regression coefficient; SE, standard error. The model was adjusted for age, sex, education level (< 6 years, 6–12 years, or > 12 years), marital status (married or other), residence status (living alone or not), monthly income, sleep quality, handgrip strength (HGS), appendicular skeletal muscle mass index (ASMI), body mass index (BMI), history of stroke, osteoporosis, comorbidity and polypharmacy.

Table 3 also presents the multiple linear regression results of the associations between OF with its items and IC domain scores. The OF score was negatively associated with the vitality domain score (β=-0.134, p = 0.018) and locomotion domain score (β=-0.140, p = 0.011) and positively associated with the psychological domain score (β = 0.247, p < 0.001) but not with the cognitive or sensory domain score. Among the OF items, the inability to chew hard food was associated with a greater likelihood of having a lower locomotion domain score (β=-0.122, p = 0.028) and a higher psychological domain score (β = 0.151, p = 0.018), and brushing teeth less than twice was associated with a greater likelihood of having a lower cognitive domain score (β=-0.168, p = 0.006) and a lower sensory score (β=-0.126, p = 0.029), less frequently going out was associated with a greater likelihood of having a lower locomotion domain score (β=-0.202, p < 0.001). There was no correlation between the three OF items above and the other IC domains.

Figure 2 shows the adjusted association between OF with its items and the likelihood of worse IC in all participants. According to our two multiple logistic regression models, worse IC was associated with OF score (OR=1.380, 95% CI: 1.080–1.763), OF (OR=5.321, 95% CI: 1.598–17.717), inability to chew hard food (OR=6.153, 95% CI: 2.229–16.983) and brushing teeth less than twice a day (OR=3.515, 95% CI: 1.086–11.378). Additionally, no significant associations were detected between other OF items and the likelihood of worse IC.

The above models were adjusted for age, sex, education level, marital status, residence status, monthly income, sleep quality, HGS, ASMI, BMI, history of stroke, osteoporosis, comorbidities, and polypharmacy.

This cross-sectional study is the first to investigate the relationship between OF and IC. Our results revealed that OF increased the risk of a decline in IC domains (vitality, locomotion, and psychology) and was an independent predictor of IC decline. Additionally, OF items (inability to chew hard food, brushing teeth less than twice a day and less frequently going out) were the most susceptible to the impact of IC decline. This result emphasizes the clinical importance of OF in protecting older individuals from IC deterioration or even reversing it.

The prevalence of OF is 8.4%-22.5% in Japanese community-dwelling older adults [28–31]. However, a greater prevalence (44.2%) was found in this investigation, which is close to the 41.3% reported in a Chinese community-dwelling population in Yangzhou city (41.3%)[12]. Additionally, a higher prevalence (69.0%) of OF was reported at Chinese community hospitals [32]. Several possible explanations for the higher rate of OF in Chinese older adults include (i) different tools used for assessing OF status, (ii) higher levels of comorbidity and polypharmacy for patients in hospital settings, and (iii) weaker awareness of oral health among older adults in China.

61.1% of the population had IC impairment. The rate observed in this study was similar to that reported at Xuanwu Hospital (69.1%)[33], although it was higher than that expected among populations residing in communities (39.9%) [34], which may be attributed to complex multimorbidity and multiple functional losses among older patients in hospital settings.

Vitality interacts with other IC domains and is a fundamental physiological determinant of IC[35, 36]. Our multiple linear regression analysis revealed that OF was negatively associated with vitality. In line with our findings, several previous studies have demonstrated that OF increases the risk of malnutrition by changing dietary variety and food satisfaction [15, 31, 37]. In turn, poor dietary intake can further increase the risk of periodontal disease, which is the primary cause of tooth loss, due to a lack of fatty acids, vitamin C, vitamin E, beta-carotene, fiber, calcium, dairy, fruits, and vegetables[38]. However, no association was observed between vitality and OF (inability to chew hard food) in the current study, which was inconsistent with previous studies showing that chewing problems resulted in nutritional deficiencies (less energy, carbohydrates, protein, and fat) and gastrointestinal disturbances[39, 40]. One possible explanation is that the nutritional status of the patients was affected by complex multimorbidity in hospitalized older patients or that the assessment of chewing ability was self-reported rather than instrumentally measured. Locomotion, which is evaluated with the SPPB test including gait time, chair stand, and balance, reflects one’s physical performance [41]. In a study conducted by Iwasaki et al.[42], comprehensive gait characteristics in association with OF have been examined, indicating that the older adults with OF showed poor gait performance, mirrored by slow gait speed, accompanied by short stride and step lengths and long double support duration. Song et al. [12] revealed that oral frailty plays a significant role in increasing the likelihood of falls, which is partially mediated by nutritional status. Furthermore, a two-year longitudinal study revealed that oral frailty was associated with increased risks of poor physical performance, such as physical frailty and disability[30]. These findings are consistent with the results of the present study, which revealed that OF was related to locomotion capacity. Among the OF items associated with IC, the inability to chew hard food and less frequently going out were related to locomotion capacity. As previously reported, malnutrition induced by chewing difficulty was associated with low muscle strength and low muscle performance [43], or individuals with malocclusion showed worse postural stability and a tendency to shift their center of gravity [14]. Additionally, during the survey, many older patients reported that they went out less due to physical discomfort, which, in turn, can further lead to a decline in physical function. The association between OF and psychological capacity was expected. Similarly, Lin et al. reported that oral frailty was significantly associated with late-life depression in community-dwelling older adults in a dose-response manner[44]. In addition, OF item (inability to chew hard food) was significantly associated with psychological capacity. Chewing difficulty may have an adverse effect on one's social and emotional well-being and may be linked to negative feelings such as despair, sadness, and depression. The biological plausibility of chewing difficulty leading to depression is related to the hypothalamic‒pituitary‒adrenal axis[45] and metabolic syndrome[46]. The associations between cognition and OF and the inability to chew hard food were not observed in the present study, although enormous evidence has shown that mastication maintains peripheral sensory input along with general health and increased blood supply in different brain regions, providing physiological benefits to central nervous system cognitive areas[47]. For inconsistencies, we speculate that older adults with mild cognitive impairment (MCI) (12.5%) are too few to see a difference. However, a correlation between brushing teeth less than twice a day and cognition was observed and closely aligns with previous findings, which indicated that inadequate oral hygiene behaviors might contribute to cognitive decline due to poor periodontal status[48, 49]. IC was related to brushing teeth twice a day but not regular attendance of dental clinic, indicating that daily oral hygiene behavior was more essential to managing IC than regular attendance at a dental clinic. For sensory capacity, a correlation between OF and sensory capacity was not observed, although brushing teeth less than twice a day was associated with sensory capacity. To date, few studies have explored the relationship between sensation and OF; hence, further research is necessary to obtain more detailed information regarding the specific associations between visual or hearing impairments and OF.

The ICOPE approach focuses on optimizing intrinsic capacity and functional ability as the keys to healthy aging. However, healthy aging cannot be achieved without maintaining oral health and function[1]. As called for by the FDI World Dental Federation, oral health promotion and oral healthcare should be integrated into noncommunicable disease strategies and universal health coverage benefit packages[50]. In our study, IC was related to OF, especially its items (inability to chew hard food, brushing teeth less than twice a day, and less frequently going out), implying that OF may be identified and treated to prevent or delay the development of IC decline. Lu et al. reported that oral function interventions significantly improved physical fitness among potentially dependent older adults[51]. Another trial has shown that masticatory exercises improve cognitive function in healthy older adults[52]. Furthermore, the “Program to Improve Oral Functions” under the Community Support project has been included in the “Prevention of Long-term Care” project in Japan[53]. In this context, the prevention of IC decline can be strengthened by integrating oral health into the ICOPE plan, especially its locomotion, vitality, and psychological domains. Hence, we must seize the chance to enhance people’s health outcomes and lower total health system costs through early and affordable oral health interventions.

Strengths and Limitations

Our study had several strengths. First, this study was the first to examine the relationship between OF and IC. Second, the data were collected by trained nurses, ensuring the validity and consistency of the data. Third, we adjusted for many important confounding variables, including age, sex, residence status, monthly income, marital status, years of education, sleep quality, polypharmacy, comorbidity, BMI, HGS, and ASMI. This helped us to provide more objective results. Nevertheless, several limitations should be acknowledged. First, the sensory domain was evaluated via subjective measurements, which may have introduced potential biases and inaccuracies in the data. Second, the study population was narrow and comprised older patients from a single geriatric department, which may limit the applicability of the results to other demographics. Third, the cross-sectional study design made it difficult to identify causal linkages or establish temporal relationships between the variables. Consequently, more multicenter, longitudinal research is needed to clarify the dynamic characteristics of the interactions examined in the current study.

In this study, IC deficits were independently associated with OF in older patients, especially for its items (inability to chew hard food, brushing teeth less than twice a day, and less frequently going out). The findings suggest that integrating oral health into the ICOPE plan is essential for identifying older adults at risk of IC deficits and providing preventive care.

Compliance with ethical standards

This study was approved by the Ethics Committee of the Geriatric Hospital of Nanjing Medical University (Ethic number: 2020025). All participants provided informed consent before they participated in the study. This study was performed following the Declaration of Helsinki.

Declaration of Competing Interest

Chunyan Huang, Lingzhi Zhu, Xiaolan Shi, Haiqiong Zhu, Xiaoxing Shen and Xiaojun Ouyang declare that they have no conflict of interest.

Acknowledgments

We sincerely thank Xiaojun Ouyang and the staff from the Geriatric Department of the Geriatric Hospital of Nanjing Medical University for their positive guidance and involvement in this study.

Funding statement

This research was funded by the Jiangsu Population Association (JSPA2019023) and the Jiangsu Elderly Health Research Project (LSD2022001).

Clinical trial number

Not applicable.

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No competing interests reported.

Association between Oral Frailty and Intrinsic Capacity among Older Patients

Status:

Version 1

Abstract

Figures

Introduction

Methods

Study design and participants

IC assessment

Oral frailty assessment

Covariates

Data analysis

Results

Characteristics of the participants

Relationship between OF and IC

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1