Diabetes and its complications are a major cause of morbidity and mortality worldwide and contribute substantially to health care costs. The major complications of DM are divided into: microvascular (retinopathy, nephropathy and neuropathy) and macrovascular complications (cardiovascular diseases and lower-extremity amputation). It has been proposed by Loe25 that periodontitis would be the sixth complication of diabetes. According to the Consensus Report of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions26, there are no characteristic phenotypical features that are unique to periodontitis in patients with DM, so the level of glycaemic control in diabetes influences the grading of periodontitis and it should be included in a clinical diagnosis of periodontitis as a descriptor. In addition, most of the evidence for its adverse effects on periodontal tissues is from patients with T2DM. However, the level of hyperglycaemia over time, irrespective of the type of diabetes, is of importance when it comes to the magnitude of its effect on the course of periodontitis26. Therefore, the aim of this chapter is to discuss the evidence for the bidirectional association, epidemiology and mechanisms linking periodontitis, obesity and DM.
SUMMARY
● Worldwide, more than 1.9 billion adults are overweight and, of these, over 650 million are obese.
● Overweight and obesity have genetic, behavioural, socio-economic and environmental origins.
● Paradoxically, coexisting with undernutrition, an escalating global epidemic of obesity – also known as ‘globesity’ – is taking over many parts of the world.
Annually, the cost of globesity is around US $190 billion per year in the USA and €10.4 billion in Europe.
1.2.1 Periodontitis and obesity
The association between obesity and periodontitis was first reported in 1977, when changes in the periodontium of obese rats was found27. The first human study reporting this relationship was conducted by Saito et al28. In this study, the periodontal status of 241 healthy Japanese subjects was assessed. The authors observed that the relative risk of periodontitis was 3.4 in subjects with BMIs of 25.0 to 29.9 kg/m2, and 8.6 in those with BMIs of ≥ 30 kg/m2, compared with subjects with BMIs of < 20 kg/m2 28. Since then, some systematic and non-systematic reviews have been published regarding this association. However, the level of evidence is low, as they include mainly cross-sectional studies, whilst prospective evidence is scarce29. In addition, there are several confounding factors related to obesity that should be clarified to elucidate the direction of this association. In a systematic review, Moura-Grec et al30 found an association between periodontitis and obesity in 17 studies, a trend in 8 studies, and no association in 6 studies. When they compared normal weight, overweight and obesity, they observed an odds ratio (OR) of 1.30 (95% confidence interval [CI] 1.25 to 1.35) of the risk to have periodontitis in an obese subject. Data from a systematic review by Keller et al29 including interventional and longitudinal studies showed that overweight31, obesity31,32, weight gain32 and increased waist ratio27,28 are risk factors directly associated with developing or worsening periodontitis.
Jimenez et al31 examined the association between measures of adiposity and self-reported periodontitis, using data from more than 36,000 healthy male participants of the Health Professionals Follow-Up Study, who were periodontally healthy at baseline and were followed for more than 20 years. They observed that overweight and obesity increase the risks of having periodontitis (hazard ratio [HR] 1.09, 95% CI 1.01 to 1.17, and HR 1.30, 95% CI 1.16 to 1.45, respectively). When the obesity data was broken down among dental and non-dental professionals, they only observed a significant association in the first group (HR 1.52, 95% CI 1.32 to 1.75 vs. HR 1.07, 95% CI 0.90 to 1.27). Regarding the waist ratio, subjects with more than 40.25 inches in waist circumference exhibited a 25% (95% CI 1.09 to 1.44) increased risk of periodontal disease compared with men with less than 40.25 inches. All data were adjusted by age, number of teeth at baseline, physical activity or fruit and vegetable intake. It is important to highlight that periodontitis was self-reported in this study, thus the lack of an expert diagnosis is likely to introduce some errors and biases in the study outcomes.
Gorman et al32 found that a 1% increment in waist-to-height ratio was associated with a 3% increase in the HR of having periodontitis progression over 27 years, and an augmentation of 1 cm in waist circumference was associated with a 1% to 2% increase in the hazard of periodontitis in 1038 white males. Obese subjects had an HR of 1.52 (95% CI 1.05 to 2.21) for having clinical attachment loss greater than 5 mm and an HR of 1.60 (95% CI 1.07 to 2.38) of having alveolar bone loss greater than 40% of more than two teeth when compared to normal weight counterparts. Furthermore, treatment outcomes may be diminished by obesity: Martinez-Herrera et al33 reported, in their systematic review, that obesity had an impact on the outcome of scaling and root planing in patients with periodontitis in three of the 28 studies included. On the other hand, six studies did not show this impact. Conclusions are difficult to draw because of the high methodological heterogeneity in terms of evaluation of the periodontitis outcome measures used, risk factors analysed, and age and gender of the participants in the different studies. In a cross-sectional study published by the same group, the authors observed that periodontitis was more prevalent in obese subjects (80.9% vs. lean 41.2%), with a six-fold increased risk of having periodontitis. In addition, obese subjects displayed higher diastolic blood pressure, increased circulating tumour necrosis factor alpha (TNF-α) and high-sensitivity C-reactive protein (hsCRP), as well as lower high-density lipoprotein (HDL) than lean subjects. Interestingly, obese subjects with insulin resistance had higher systolic blood pressure, higher glucose, insulin, HbA1c and triglyceride levels, more insulin resistance (HOMA-IR [homeostatic model assessment of insulin resistance]), and a higher number of teeth with probing depths greater than 4 mm than those obese subjects without insulin resistance34.