Association between Obesity and Dental Caries in Adults: An Analysis of WHR, and DMFT Score

The World Health Organization (WHO) defines health as a condition of physical, mental, and social well-being rather than the absence of disease or infirmity [1]. Modern definitions include diet as an important factor. Diet plays a crucial role in the development and prevention of various diseases including oral diseases, obesity, and systemic diseases.

Obesity is a health condition resulting from excessive body fat [2]. A global pandemic affects individuals of all ages and income levels [3]. According to the WHO, obesity was the fifth leading cause of death worldwide in 2018, with individuals with obesity accounting for 13% of the global population [4]. Some of the main causes of obesity are lack of physical activity, overeating, genetic factors, and the use of certain medications [2, 5].

The repercussions of obesity extend beyond its impact on general health. Numerous studies have established a strong association between obesity and chronic diseases, including metabolic syndrome, type 2 diabetes mellitus, insulin resistance, cardiovascular diseases, and dyslipidemia [6]. As such, people with obesity face a diminished life expectancy compared to their healthy counterparts with normal body mass index (BMI) scores [6]. The complex relationship between obesity and health encompasses both oral and general health, driven by common risk factors such as socioeconomic status and lifestyle choices [7].

Because both obesity and dental caries are affected by excessive sugar consumption, researchers believe that individuals who are overweight and individuals with obesity are at a higher risk of developing dental caries [8, 9]. However, the complex nature of obesity and dental caries, including various genetic, cultural, socioeconomic, biological, lifestyle, and environmental factors, makes determining their exact relationship challenging [10].

Studies examining the relationship between obesity and dental caries have mostly focused on children and adolescents. Children with normal weight tend to have fewer caries in the primary dentition than in the permanent dentition, while children with obesity are more likely to experience tooth loss [11‒13].

However, these findings are not consistent among adults [14]. Some studies have demonstrated a negative association [15, 16], whereas others have demonstrated no [17, 18] or a positive association [17, 19]. For this reason and due to scarcity of study examining this association in adults, we believed that more studies are needed.

In addition to excessive sugar intake, studies indicate that individuals with high BMI may visit the dentist less frequently potentially owing to perceived stigma, social inferiority, and shame, thereby resulting in an increased incidence of dental caries [20, 21]. This study aimed to examine the association between obesity and dental disease (decayed, missing, filled teeth [DMFT] score) while controlling for important confounding factors to gain a clearer understanding of this association.

This study employed demographic, oral health, body measurement, and dietary interview data from the 2017 to March 2020 pre-pandemic cycle of the National Health and Nutrition Examination Survey (NHANES) [22]. The NHANES is a complex, multistage, probability-based survey conducted by the National Center for Health Statistics targeting the noninstitutionalized civilian population of 50 states and District of Columbia in the USA [23].

The total number of participants after merging the datasets was 15,560. The study included only adults over the age of 20 years, with a total of 8,584 individuals; of these, 8,144 participants who underwent a complete examination and interview were included in the final analysis.

The main predictor was obesity, which was defined using three different measurements: waist-to-hip ratio (WHR), BMI, and waist circumference. WHR was calculated using the following formula: waist circumference/hip circumference. The results were then categorized by sex into individuals with normal weight and individuals with obesity; abdominal obesity was defined as a WHR >0.90 and >0.85 for males and females, respectively [21]. Individuals with normal weight or individuals with obesity were categorized based on a cut-off value of a BMI of 25 for obesity [24].

Caries was diagnosed according to the criteria described by Radike [25]. Pit and fissure caries were diagnosed upon detecting a catch under moderate pressure by the explorer, accompanied by softness or opacity in the surrounding area. Smooth surface caries were identified through decalcification or white spots, confirmed by explorer penetration or by scraping the area with an explorer. Smooth surface criteria were used for the visible areas of the proximal surfaces. Caries in inaccessible areas of the anterior teeth are ideally detected upon a break in the enamel; moreover, transillumination can be very helpful in the detection of caries in these sites. An enamel break in the posterior teeth indicates a positive diagnosis. Missing teeth were considered in the DMFT score if the tooth was extracted owing to caries. However, distinguishing these from teeth extracted for periodontal problems is challenging. Therefore, no distinction was made between these causes at the time of examination. Filled surfaces were identified if a permanent or temporary restoration was placed for treating caries [25]. The DMFT score was employed as a continuous variable for the analysis.

The analyses explored the following potential confounding variables: sex, race, age, family income-to-poverty ratio, ethnicity, education level, marital status, flossing status, and sugar intake. Age was dichotomized as <60 years or >60 years. Race was categorized as non-Hispanic White, Mexican or Hispanic, non-Hispanic Black, or other, including Asian and multiracial. We grouped the family income-to-poverty ratio into three groups based on the poverty line: below poverty line, <1; at or near poverty line, 1–2; and above poverty line, >2. Flossing status was categorized as regular if flossing was performed daily or more than once a week, occasional if flossing was performed once a week, or never if no flossing was performed. A mean sugar intake of 2 days was also included in the analysis.

Statistical Analysis System (SAS) software version 9.4 was used to conduct all statistical analyses. Descriptive statistics as means and frequencies were used to report the sample characteristics. Chi-square and independent t tests were used to examine the crude associations among dental caries, obesity measures, and sociodemographic characteristics.

Stata version 12.1 software (StataCorp LP, College Station, TX, USA) was used to formulate a zero-inflated negative binomial regression model to predict the DMFT score based on the obesity measurements and sociodemographic variables. Initially, we tested each variable individually in relation to the DMFT score to understand its individual predictive power. BMI demonstrated no statistical association with the DMFT score (p = 0.68); thus, WHR was used as the main predictor in this study.

Subsequently, we explored different combinations of variables with WHR to enhance DMFT score prediction. Interestingly, we observed a significant shift in the model’s dynamic upon introducing age as a variable. Once age was included, WHR stopped showing a statistically significant association with the DMFT score. This resulted in the development of two distinct models. The first model included age as a predictor, which negated the influence of WHR on DMFT score, whereas the second model excluded age, maintaining WHR’s association with the DMFT score.

Throughout the analysis, survey procedures and sample weights were used to accommodate the complex NHANES sampling design and produce representative national estimates. The significance level was set at 0.05.

Most participants were classified as individuals with obesity based on the WHR (74.5%) or BMI (72.7%), with a mean waist circumference of 97 cm. Notably, 83.2% of those categorized as individuals with obesity by BMI were also considered individuals with obesity by WHR, whereas 42.1% of those with BMI-defined obesity had a normal WHR (Tables 1, 2).

Compared to the total population, the majority of individuals with obesity were males (51.6%) with increased age (34.7%). In contrast, individuals with a normal WHR were predominantly younger females (61.7%), with a significant proportion being under the age of 60 years (84.3%), Black (15.7%), and more educated (37.5%), and single (33.8%) (Table 1).

Bivariate analysis demonstrated a statistically significant difference in the DMFT score and missing teeth between the individuals with normal weight and individuals with obesity (p < 0.0001). However, the mean filled and decayed teeth were similar in both groups (p = 0.78 and p = 0.96, respectively) (Table 2).

After adjusting for the sociodemographic variables, WHR was no longer associated with the DMFT score; however, individuals with obesity had higher DMFT scores (β = 0.11, 95% confidence interval [CI] = −0.01 to 0.23). Factors, such as older age, female sex, and divorced/widowed/separated status, were associated with higher DMFT scores. In contrast, higher education level, living at the poverty line, being Mexican American or Hispanic, and regular flossing were associated with lower DMFT scores (Table 3, model 1).

Removing age from the regression model reinstated WHR’s significant association with the DMFT score, revealing a higher estimate (β = 0.17, 95% CI = 0.05–0.30). Marital status and poverty also influenced the DMFT score differently in this adjusted model, with married or partnered individuals showing increased DMFT scores (β = 0.18, 95% CI = 0.05–0.32), and poverty no longer being a significant factor (Table 3, model 2).

This study investigated the association between obesity and dental caries in an adult population. Although the WHO recommends using BMI as the main criterion for measuring obesity [26], we used WHR and BMI to ensure a more comprehensive understanding of this association. Overall, the findings indicated a positive association between obesity and dental caries among adults. In terms of identifying individuals with obesity, the results of both approaches were nearly identical, as 83.2% of individuals with obesity classified using BMI were also classified as individuals with obesity using WHR.

Our study revealed a higher mean DMFT score and missing teeth among individuals with obesity than those without obesity. These results are similar to those reported previously. For instance, Ashour et al. [27] reported a positive association between obesity and dental caries, with higher mean DMFT scores in individuals with obesity than in those with normal BMI/WHR. Similarly, two studies by Hilgert et al. [28] and Prpić et al. [29] revealed that a greater number of missing teeth was associated with higher BMI.

Different assumptions have been made in the literature to explain this association. This intertwining of poor oral health and overall health, particularly in adults and the elderly, underscores the shared risk factor concept proposed by Sheiham and Watt [7, 30]. Changes in the diet and loss of essential nutrients can precipitate oral diseases, potentially resulting in tooth loss. Conversely, tooth loss and reduced number of teeth (<20) can affect the masticatory efficiency and dietary habits, potentially influencing the BMI [31‒35]. Moreover, the association between obesity and oral health can unfold in two directions. Oral disease can impede the ability of maintaining a regular, nutrient-rich diet, potentially leading to a shift toward a softer, sugar-rich diet promoting obesity [36, 37]. Conversely, obesity is often linked to a diet high in sugary and unhealthy foods, which fosters the growth of cariogenic bacteria and development of dental caries [38]. In addition, some authors have reported higher DMFT scores in individuals with obesity, possibly due to feelings of stigma [21, 39].

On the other hand, one study by Song et al. [15] revealed an inverse association between dental caries and obesity when examined in the adult Korean population. Several factors may account for the differences between the results of our study and those of the Korean study, including dietary habits, genetic and biological factors, healthcare access and preventive care, cultural practices, and environmental and policy factors. For instance, dietary habits differ significantly between the two populations: in the USA, diets tend to be high in sugary and processed foods, whereas, in Korea, the traditional diet is lower in sugar and processed foods and focuses more on vegetables, rice, and fermented foods. Additionally, genetic predispositions have been shown to influence both obesity and dental caries. Furthermore, oral microbiota varies among populations, which can affect susceptibility to dental caries in different ways.

Our study also revealed a significant association between higher DMFT scores and older age, female sex, and being divorced/widowed/separated. This result is similar to that of a Korean study that demonstrated a positive association between obesity and advanced dental caries, specifically in women and elderly individuals [40‒42]. This could be related to the DMFT score being a cumulative index, which means that individuals will show higher DMFT scores with increasing age; moreover, since individuals with obesity are at a higher risk of having high DMFT scores, older individuals with obesity will also be at a higher risk [43, 44].

Considering the female sex, some authors have attributed hormonal changes that affect the quality and quantity of saliva to the increased possibility of higher DMFT scores [41, 42]. A possible explanation for the higher odds of DMFT scores in the widows/separated and divorced groups could be related to a combination of psychological, social, and behavioral factors that are often correlated with marital status changes. A direct association between the DMFT scores and divorce or separation has not been reported in previous studies [45]. However, our study provides evidence that a combination of psychological stress, changes in dietary habits, economic challenges, and obesity could lead to higher DMFT scores in widowed, separated, and divorced individuals. For example, this group experienced significant emotional and psychological stress that could lead to self-neglect in terms of personal care and oral hygiene. In addition, financial and dietary habit changes could deteriorate oral and general health by limiting access and dental care utilization and result in a shift toward a more sugary and unhealthy diet. Lifestyle changes and smoking and alcohol consumption as coping mechanisms to overcome these problems could significantly contribute to worsening oral health [45].

Interestingly, our results showed no significant association between the WHR and DMFT scores after adding age to the regression model. The change in the significance of this association can be attributed to several factors. Age could be a key confounding factor as it could be related to both the likelihood of obesity and occurrence of dental caries. Age is also a strong determinant of many health outcomes, including obesity and DMFT scores. Its removal from the model may have oversimplified the relationship between these variables, ignoring the potential effect of modification or interaction of age on the relationship between obesity and dental caries. The possibility of the correlation of age with WHR was tested to exclude this possibility, demonstrating no correlation.

To our knowledge, this is the first study to shed light on the association between obesity and dental caries in the adult population in the USA using nationally representative data with a high response rate. The use of a zero-inflated multinomial regression to predict the association between DMFT scores and obesity adds to the statistical power of the study, as it provides better predictions and estimates owing to its improved capacity to handle excess zeros, differentiate between the types of zeros, and deal with overdispersion in the data. Moreover, our study used BMI and WHR to determine this association, which provided a more comprehensive explanation of this relationship.

One of the limitations of this study was its cross-sectional design, which did not allow for causal inferences. Additionally, the use of DMFT scores could exaggerate the results, especially in older patients, as it is a cumulative and nonreversible measure of dental caries [44].

This study highlights the importance and close association of oral and general health. This association should influence and motivate health practitioners, including dentists, physicians, and public health practitioners, to increase awareness by providing information and promoting health. In addition, we should direct our vision toward a more comprehensive approach such as, instead of conducting separate campaigns on obesity, diet, lifestyle, and dental health, a more comprehensive and collaborative approach toward oral and general health should be adopted. Dental health professionals, including pediatric dentists and public health practitioners, should take a more proactive role in educating communities about healthy dietary habits, effective oral hygiene practices, and navigating the healthcare system. By providing this essential guidance, they can significantly reduce the impact of obesity on both oral and general health. Furthermore, the emphasis should shift from curative to preventive care, with the implementation of comprehensive school-based programs that promote fluoride use, dental sealants, physical activity, and proper oral hygiene. These preventive measures are crucial in fostering long-term health and well-being.

Obesity was positively associated with dental caries in a representative sample of adults in the USA. However, age may have been a confounding factor in this relationship. Further longitudinal and multinational studies are warranted to determine the possible reasons for this association and further explain the associated factors.

The authors, therefore, acknowledge with thanks DSR for technical and financial support.

Ethics approval was not required as this is nonhuman subject research as it is using completely de-identified publicly available dataset (NHANES), thus informed consent was not required for this study. NHANAES have their own IRB approvals, for this cycle, the IRB protocol numbers are #2011-17 and #2018-01.

The authors have no conflicts of interest to declare.

This study was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, under grant no. (GPIP: 827-165-2024).

Alaa Jameel Kabbarah: conceptualization, data curation, validation, visualization, roles/writing – original draft, and writing – review and editing. Meyassara Samman: conceptualization, data curation, formal analysis, methodology, validation, visualization, roles/writing – original draft, and writing – review and editing. Abdulraheem A. Alwafi, Heba Ashi, Layla Waleed Abuljadayel, Lina O. Bahanan, Mona T. Rajeh, and Nada J. Farsi: conceptualization, validation, supervision, and writing – review and editing.

Publicly available datasets were used in this study. These can be found at https://wwwn.cdc.gov/nchs/nhanes/continuousnhanes/default.aspx?Cycle=2017-2020 [22].