1. Introduction
According to the World Health Organization [
1], oral health is a key indicator of overall health, well-being, and quality of life. Several studies have shown that oral and general health are strongly interlinked [
2,
3,
4,
5]. In fact, systemic disorders such as cardiovascular diseases [
4], cancer [
5], chronic respiratory diseases [
2], and diabetes mellitus [
3] share common modifiable risk factors with most oral diseases and conditions. Tobacco use, alcohol consumption, and diets high in free sugars are among these risk factors, all of which are increasing at the global level [
6].
Furthermore, deteriorating oral health, especially in older age, together with a reduction in oral hygiene, may lead to a progression of caries and periodontal disease resulting in tooth loss, which can in turn lead to changes in diet and nutritional health [
7]. The reduction in the number of teeth is accompanied by different food choices as partially or fully edentulous patients tend to prefer softer over hard foods, which may have lower nutritional values. Macro- and micronutrient deficiencies resulting from these nutritional imbalances are linked to functional impairment in both underweight and overweight older adults, increasing the risk of falls, fractures, infections, frailty, and dementia [
8,
9,
10,
11].
However, an assessment of oral clinical indicators alone is often not adequate to correctly describe health status, especially concerning emotional aspects. On the other hand, it has been reported that individuals with chronic debilitating diseases can consider their quality of life to be higher than healthy people, implying that bad health or sickness does not always reflect a low quality of life [
12,
13]. In recent years, the assessment of oral health-related quality of life (OHRQoL) has been widely used to evaluate the impact of an individual’s oral health on the patient's physical and psychosocial status, including a self-assessment of emotional well-being, expectations, and therapeutic satisfaction, becoming a relevant component of chronic disease management [
13,
14]. One of the most widely used tools for assessing OHRQoL is the Oral Health Impact Profile-14 (OHIP-14) questionnaire, including 14 items within seven domains related to functional limitation, physical pain, psychological discomfort, physical, psychological, social disability, and handicap [
15]. This is a shorter version of the OHIP-49 [
16]. A recent study examined the nutritional characteristics of older adults and their relationship to OHRQoL, measured by the Geriatric Oral Health Assessment Index (GOHAI), showing that individuals with a poor perception of their oral health were more likely to have an unfavorable body mass index (BMI) [
17], i.e., BMI ≤18.4 kg/m2 (underweight), BMI between 25.0 and 29.9 kg/m2 (overweight), and BMI ≥30.0 kg/m2 (obese). However, at present, there is a lack of evidence on whether a negative OHRQoL may have an impact on BMI changes. The first aim of the present study was to evaluate the association between subjective OHRQoL, measured with the OHIP-14, and unfavorable BMI in a large population-based study on older adults from Southern Italy. The second aim was to assess which of the seven domains of the OHIP-14 questionnaire (namely functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap) was most strongly associated with higher variations in BMI and, therefore, with an increased clinical occurrence of underweight or overweight/obesity in older age.
4. Discussion
In the present large population-based study on older adults from Southern Italy, negative OHRQoL, i.e., discomfort and disability attributed to oral conditions, increased the risk to have an unfavorable BMI in the hierarchical logistic regression models both unadjusted and also when adjusted for age, sex, education, hypertension, carbohydrate consumption, and alcohol consumption. Furthermore, higher age was linked to a decreased risk to have an unfavorable BMI. The most important predictive domains/sub-scales of OHIP-14, measuring OHRQoL, for unfavorable BMI, were, in decreasing order of importance, physical pain, functional limitation, psychological discomfort, physical disability, social disability, psychological disability, and handicap.
The principal finding of the present study was that negative OHRQoL increased the risk to have an unfavorable BMI in a large population of older adults from Southern Italy, also after adjustment for a series of possible confounding factors. In recent years, in other population-based studies, the assessment of clinical oral indicators and OHRQoL has been widely used to evaluate whether oral problems may lead to nutritional dysfunction in older age [
17,
32,
33]. In particular, a parabolic effect was found between OHRQoL and BMI in community-dwelling older adults living in Alabama, USA, with the strongest associations occurring in the underweight and obese categories [
32]. These findings were similar to those of the present study in which BMI <18.4 kg/m2 (underweight) and >30 kg/m2 (obese) were classified as unfavorable, and higher OHRQoL increased the risk to have an unfavorable BMI. However, in the present study, we did not distinguish between older individuals underweight and overweight/obese. Another study, using the GOHAI for measuring OHRQoL, found that subjects with a poor perception of their oral health were more likely to have an unfavorable BMI [
17], with a classificatory system similar to that of the present study (older individuals underweight, overweight, and obese categorized as having unfavorable BMI). Finally, in a hospital-based study on Thai older individuals, those with obesity had an almost three times higher tendency to have a negative OHRQoL compared with the non-obese [
33]. Moreover, after adjusting for all related factors, the chances of predicting a prevalence of participants who scored four on at least one item on the OHIP-14 score based on obesity and oral dryness score were 4.42 (95% CI:1.57–12.47) and 1.11 (95% CI:1.02–1.20), respectively. For every point of BMI or 1 cm increase in waist circumference, the chance of unfavorable OHRQoL also increased by a factor of 1.23 or 1.06, respectively, without the influence of xerostomia [
33]. However, in some other cross-sectional studies, there was no association between OHRQoL measurements and nutritional status among older subjects [
34,
35]. These negative findings may be partly explained by various factors affecting food choices and intakes among older subjects, like general health, socioeconomic components, and taste and control over food preparation [
36], with also a lack of knowledge on the nutritive value of foods consumed among older individuals, putting them still at risk of malnutrition regardless of their oral perceptions. Furthermore, the sample sizes in these previous negative studies were very small [
34,
35], without a comprehensive adjustment for possible confounders, and these factors could be a source of discrepancy with the present study.
Different studies showed an association between the impacts of OHRQoL and nutritional factors [
37,
38]. Older subjects with poor OHRQoL scores were shown to be at risk of nutritional deficiencies investigated with the Mini-Nutritional Assessment (MNA) [
37,
38], and not to have an actual unfavorable BMI. On the contrary, older adults with a better perception of oral health were among those at least at risk of malnutrition (lower MNA score) [
39]. Both oral health and nutritional status are strongly related to healthy behaviors, and therefore these findings may also suggest that those who have poorer oral health may be less likely to be conscious about their diet. Furthermore, in the present study, higher age was linked to a decreased risk to have an unfavorable BMI. This finding was consistent with the results from a Malaysian population-based study in which the number of older adults with unfavorable BMI significantly decreased with advancing age [
17]. This pattern may be explained by the fact that older individuals with unfavorable BMI (i.e., obesity) may die earlier because of chronic diseases related to their condition like metabolic or cardiovascular diseases, thus leaving the non-obese individuals with a higher survival rate in the older age group.
In the present study, the OHRQoL domains more linked to physical manifestations (physical pain, functional limitations, and physical disability, with their items focusing on worsened taste, interrupted meals, and discomfort to eat) appeared to have a greater impact on nutritional factors associated with an unfavorable BMI compared to psychosocial manifestations of the OHRQoL (social disability and psychological disability, with their items focusing on the difficulty to relax or to do jobs due to oral problems). Moreover, the item “uncomfortable to eat“ (domain: physical pain) and the item “irritability“ (domain: social disability) were more represented in the unfavorable BMI group if compared with the ideal BMI group. In a recent hospital-based study, using OHIP-14 to evaluate OHRQoL, the average score was highest for the physical pain domain in all studied groups [
33]. Moreover, in the same study, all groups had the highest frequency of responses for the two items (item 3, pain, and item 4, uncomfortable to eat) of the physical pain domain of the OHIP-14 [
33], suggesting that a possible underlying mechanism explaining why the higher rate of dental disease in patients with obesity/underweight might be a factor related to OHRQoL. The physical pain domain is determined by pain and discomfort when eating. The present findings are also consistent with a previous study in Norway showing that older individuals most frequently experienced problems with pain in the mouth and discomfort when eating [
40]. Therefore, oral pain may lead to a negative OHRQoL in older adults who may experience difficulty chewing and swallowing due to dry mouth, missing teeth, and dental and periodontal problems resulting in discomfort while eating and drinking [
41,
42].
The strengths of the present study were the population-based setting and the large number of older subjects included, notwithstanding a relatively small number of those investigated with the OHIP-14. However, given the cross-sectional nature of the study, we cannot make any inference on the direction of the association because of reverse causality; we can estimate the association only in terms of prevalence. Other studies showed no statistically significant differences in BMI between individuals with at least one tooth and persons with no teeth [
32,
43]. Therefore, dentate status was not included in the present analysis. Furthermore, the OHIP-14 items were self-reported and consequently, subjective. However, they provide important information on the perceptions of OHRQoL in older adults, and self-reported measures may be more meaningful than clinical measures in this context [
32]. Finally, the present findings may not be generalizable; therefore, these results should be cautiously interpreted.
Author Contributions
Conceptualization, V.D. and F.P.; methodology, F.P. and R.S.; software, F.C.; validation, V.D., F.P., F.L. and M.L.; formal analysis, F.C.; investigation, V.D., R.Z. and A.D; data curation, V.D., F.P and M.L; writing—original draft preparation, V.D., F.P and F.L; writing—review and editing, F.P., A.P. and D.M.; supervision, F.P, V.S. and F.L.; project administration, V.S and A.P.; funding acquisition, R.S. All authors contributed to drafting, revising and approving of the submitted manuscript. All authors have read and agreed to the published version of the manuscript.