The Relationship Among Obesity, Diabetes, and Oral Health: a Narrative Review of Real-World Evidence

Periodontal disease is an inflammatory condition caused by periodontal pathogens and constitutes a leading cause of tooth loss in adults [1]. This disease leads to tooth loss through prolonged inflammation in periodontal tissues, which activates osteoclasts and results in resorption of the alveolar bone that supports the teeth. According to the Global Burden of Disease study, oral diseases affect 3.5 billion people worldwide [2], and the majority of cases can be attributed to untreated dental caries and periodontitis [3]. It is estimated that over 50% of U.S. adults have periodontal disease, depending on the disease definition, which substantially impacts their quality of life [4]. A survey of dental diseases in Japan revealed that more than 40% of individuals aged 45 or older had periodontal pockets measuring 4 mm or greater [5]. Severe periodontal disease is considered the sixth-most prevalent health condition worldwide, affecting 743 million people [6]. The global prevalence of untreated dental caries is 34.1%; increasing rates are observed in low- to middle-income countries [2]. Although the combined burden of oral conditions has declined in more economically developed nations, it has risen in less economically developed countries, indicating disparities in oral health outcomes among regions [3].

Previous studies have partially elucidated the relationship among diabetes, obesity, and periodontal disease [7‐9]. Adipocytes play a key role in energy storage and produce various adipocytokines. Visceral fat accumulation disrupts adipocytokine balance, inducing chronic inflammation and insulin resistance (Fig. 1). Although insulin resistance is a primary factor in diabetes, periodontal disease reportedly also contributes to systemic insulin resistance, as measured by the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR), through prolonged inflammation in periodontal tissues [10, 11]. However, the numbers of remaining teeth and retention rates among tooth sites in individuals with diabetes or obesity remain poorly understood. One challenge in clarifying these relationships is that analyses using the number of remaining teeth as an outcome are strongly influenced by factors such as age and sex, hindering effective stratification of risk factors in studies with limited sample sizes. This review summarizes the studies of the impacts of diabetes and obesity on oral health, with a focus on the number of remaining teeth, by using a large database created by linking dental visit records from insurance claims with health check-up results.

Bild vergrößern

A meta-analysis of 15 cohort studies revealed that individuals with periodontal disease had a significantly increased risk of developing diabetes, with a summary relative risk of 1.26 among 427,620 participants. Conversely, in a cohort of 295,804 individuals, participants with diabetes exhibited a 1.24-fold higher summary relative risk for developing periodontal disease relative to participants without diabetes [12]. This evidence implies a bidirectional relationship between periodontitis and diabetes [12]. Patients with diabetes are considered more susceptible to periodontal disease, likely due to hyperglycemia-induced impairments in immunity and resistance to periodontal pathogens. Periodontal disease is more prevalent among individuals with diabetes [7, 8, 12, 13], and poor glycemic control is associated with greater periodontal disease severity [8, 14, 15]. Both type 1 and type 2 diabetes are associated with higher risks of tooth loss; poorly controlled diabetes further amplifies the risks of periodontal disease and tooth loss [9, 16]. Treatment for diabetes has been shown to improve periodontal inflammation and related parameters [17, 18]. Periodontal inflammation can aggravate systemic conditions by releasing pro-inflammatory cytokines, contributing to insulin resistance and worsening glycemic control. Individuals with periodontitis exhibit a higher risk of developing diabetes [12, 19]. Furthermore, meta-analyses and reviews have demonstrated that periodontal treatment effectively improves glycemic control in patients with diabetes [20‐23]. Studies have shown that periodontal therapy can enhance insulin sensitivity, as indicated by improved HOMA-IR values, and reduce levels of high-sensitivity C-reactive protein and inflammatory cytokines [17, 24, 25].

We analyzed the relationships between the number of remaining teeth and glycemic control indices using a dataset of 230,000 individuals. This dataset was generated by matching dental visit records from employment-based health insurance claims with health check-up results. The analysis revealed inverse relationships of glycated hemoglobin (HbA1c) and fasting blood glucose levels with the number of remaining teeth [26]. This trend was evident even in individuals without a diabetes diagnosis (HbA1c levels of 5.5%–6.5% and fasting glucose levels of 110–126 mg/dL) and could be observed as early as the third decade of life [26].

A site-specific analysis of natural tooth retention showed that individuals in their 30 s with HbA1c levels < 7% were significantly more likely to lose posterior teeth than similarly aged individuals with HbA1c levels ≥ 7%. As individuals aged into their 40 s and 50 s, this pattern extended to the loss of teeth adjacent to posterior teeth and anterior teeth [27]. These findings suggest that poor glycemic control increases the likelihood of posterior tooth loss at a relatively young age, and that progression to more extensive tooth loss occurs with increasing age (Fig. 2) [27].

Bild vergrößern

Obesity exacerbates various chronic diseases, such as diabetes and atherosclerotic diseases. Obesity-induced chronic inflammation causes insulin resistance, which contributes to diabetes development while increasing the risks of periodontal disease onset and progression [28]. Additionally, multiple studies have demonstrated a relationship between periodontal disease and metabolic syndrome, a condition characterized by visceral obesity combined with hyperglycemia and dyslipidemia [29‐31]. Among the components of metabolic syndrome, hyperglycemia and obesity appear to have the strongest associations with periodontal disease risk [29]. Furthermore, the likelihood of developing periodontal disease increases according to the number of metabolic syndrome components present [29, 32]. Factors shared between periodontal disease and metabolic syndrome include elevated oxidative stress, which promotes insulin resistance, and a persistent state of chronic inflammation [33]. Another proposed mechanism underlying the increased risk of periodontal disease in obesity involves alterations in the gut microbiota and its metabolic activity [34].

The relationship between obesity and periodontal disease has been demonstrated in a health check-up study, which showed that the relative risk of periodontal disease increased according to body mass index (BMI) [35]. Similar results were obtained in the Third National Health and Nutrition Examination Survey, which analyzed data from approximately 13,000 individuals in the United States [36]. Systematic review findings reinforce the notion that obesity and increased waist circumference are significant risk factors for the development and progression of periodontal disease [37]. A recent study involving 57,496 individuals identified obesity and nonalcoholic fatty liver disease (NAFLD) comorbidity as the most influential systemic conditions in a feature importance analysis using the eXtreme Gradient Boosting machine learning algorithm, with periodontitis as the target variable [30].

Conversely, epidemiological study results suggest that periodontal disease increases the risk of obesity by reducing masticatory function. Tooth loss impairs chewing ability, leading to a preference for processed foods high in carbohydrates that require minimal chewing, thereby raising the risk of obesity [38, 39].

Our study also revealed an association between increased BMI and a decline in the number of remaining teeth beginning at age 40 [40]. Compared with non-obese individuals (BMI < 25 kg/m²), those with obesity (BMI ≥ 25 kg/m²) had significantly fewer remaining teeth at 10 sites (six maxillary, four mandibular) in their 30 s, 19 sites (11 maxillary, eight mandibular) in their 40 s, 24 sites (14 maxillary, 10 mandibular) in their 50 s, and 21 sites (13 maxillary, eight mandibular) in their 60 s. These findings are consistent with previous studies [41, 42] but add novel insights based on examinations of specific age groups and tooth sites.

Smoking is a significant risk factor for periodontitis, associated with both increased prevalence and severity of the disease [43‐45]. Multiple studies have established a causal link between smoking and tooth loss [46‐48]. A recent large-scale study investigating chronic diseases and tooth loss among 471,107 participants confirmed a strong association between smoking and tooth loss. It also identified significant associations with diabetes and chronic obstructive pulmonary disease (COPD)—both conditions linked to smoking—and tooth loss [49]. Intriguingly, the study showed a stronger association with COPD than with diabetes, emphasizing the effects of smoking on these outcomes.

The risk of tooth loss further increases when smoking is combined with diabetes. Smoking adversely alters the oral environment; the toxic substances in tobacco affect the oral cavity and respiratory tract while contributing to systemic chronic inflammation, including intestinal infections. Our analysis of 233,567 individuals revealed that nonsmokers with HbA1c ≥ 6.5% had a 1.83-fold increased risk of possessing fewer than 24 remaining teeth relative to nonsmokers with HbA1c < 6.5%. Among smokers with HbA1c ≥ 6.5%, the risk increased 3.55-fold compared with the same reference group [26].

A recent machine learning study identified smoking and obesity as two of the top five factors most strongly associated with periodontitis [30]. In our analysis of natural tooth retention according to site, the addition of smoking as a variable revealed an additional impact on tooth loss in locations unaffected by obesity alone. Further examination of the risk of possessing fewer than 24 remaining teeth showed a 1.47-fold increase in individuals with BMI ≥ 25 kg/m² relative to those with BMI < 25 kg/m². The risk increased by 1.35-fold when smoking status and diabetes were included as explanatory variables in the model [26].

The maintenance of good oral hygiene is a critical component of glycemic control in diabetic patients; effective glycemic control can help to prevent periodontal disease and tooth loss. This bidirectional relationship is also present among individuals with obesity and those with metabolic syndrome. Recommendations of regular dental visits for patients with diabetes and obesity, as well as screening for diabetes and metabolic syndrome in patients with periodontal disease, may prove beneficial. Smoking, a well-established risk factor for tooth loss, can decrease this risk upon cessation; former smokers have no greater risk compared with nonsmokers [49].

The combination of large-scale medical data, such as receipt information and health check-up results, used in this study has yielded important insights into oral health conditions and healthcare costs [50]. This approach holds promise for broader applications in medical and dental clinical research.

In conclusion, this study utilized a large database integrating receipt data and health check-up results to examine the effects of diabetes and obesity on dental health, focusing on the number of remaining teeth. The findings, supported by previous reports, emphasize the importance of addressing the interconnected cycle of diabetes, obesity, and periodontal disease as a key strategy to prevent tooth loss.