Correlation of salivary immunoglobulin A with Body Mass Index and fat percentage in overweight/obese children

Abstract Obesity is considered a risk factor for periodontal health due to the low- grade inflammation promoted by the increased adipose tissue. Objective: This study aimed to determine correlations and associations between gingival inflammation (Simplified Oral Hygiene Index, and Gingival Index), salivary immunoglobulin A (s-IgA), and salivary parameters (salivary flow and osmolality) in normal-weight and overweight/obese children. Material and Methods: Ninety-one children, aged 6 to 12 years old (8.6±1.9 years), were divided into two groups according to their body mass index (BMI), circumferences, skinfold measurements and body fat percentage: normal- weight group (NWG; n =50) and overweight/obese group (OG; n =41). A calibrated examiner performed the clinical examination using the Simplified Oral Hygiene Index, Gingival Index, and salivary collection. Data analysis included descriptive statistics and association tests ( p <0.05). Results: OG presented statistically higher s-IgA values compared with NWG, especially among the obese children ( p <0.05). Significant positive correlations between s-IgA and salivary osmolality in OG ( p <0.05), and between s-IgA and BMI values ( p <0.05) and body fat percentage ( p <0.05) were observed among all the children. Effect size varied from moderate for s-IgA values ( d =0.57) to large for BMI ( d =2.60). Conclusion: Gingival inflammation and salivary parameters were similar for NWG and OG; however, s-IgA presented higher values in OG, with correlations between BMI and body fat percentage.


Introduction
The prevalence of obesity has increased in recent decades and is a public health concern, given that this condition is an important risk factor for the onset of several systemic diseases. 1 In addition, obesity can alter the production and release of important defense cells, such as neutrophils, recognized as the first line of defense for periodontal tissues, and T and B lymphocytes, responsible for cellular and humoral responses. 2 The inflammatory state is reflected by an increase in circulating levels of proinflammatory proteins and occurs not only in adults but also in children and adolescents. Inflammatory mediators are secreted by the adipose tissue and the immune system, which can lead to a hyperinflammatory state. 3,4 Most oral inflammatory diseases seem to originate locally, but present predisposing systemic factors. 5 Thus, obesity is considered a risk factor for periodontal health. 6 Although systematic reviews of the literature have observed a higher prevalence of periodontal disease in obese adults, 7 few studies have investigated periodontal health in overweight/obese children and adolescents. 3,8 Gingivitis is widely prevalent in subjects of all ages, including children and adolescents, and usually precedes periodontitis. 9 Thus, general practitioners should be aware of the link between obesity and periodontal health. 10 A recent systematic review and meta-analysis suggested periodontal alterations might be associated with obesity in children. 1 Salivary immunoglobulins play an important role in inflammatory diseases of the oral mucosa. 5 Salivary immunoglobulin A secretion has a protective effect against oral bacteria, inhibiting the adhesion of microorganisms to the surface of mucosal cells, thus preventing their penetration into the organic tissues. 5,11 Studies have been suggesting an elevated s-IgA level is associated with a lower risk of developing gingivitis; 12 however, studies on this association in children remain scarce. In addition, studies have shown chronic stress promotes a decrease in s-IgA in children. 13 Therefore, s-IgA is an important biomarker of immune imbalances in children and may be related There is a known association between obesity and inflammation, 8 and periodontal disease is a rare finding in children. 10 Therefore, the purpose of this study was to determine correlations and associations between gingival inflammation, s-IgA, and salivary parameters in normal-weight and overweight/obese children classified according to Body Mass Index (BMI), skinfold measurements, and fat percentage. The hypothesis is that overweight/obese children present greater gingival inflammation and different salivary parameters compared with normal-weight children.

Sample selection
The study population consisted of children who sought dental care at a dental school in São Paulo, SP, Brazil, from October 2014 to May 2016. Healthy children of both genders, aged 6 to 12 years old, in the mixed-teething phase were selected. They were divided into two groups: normal weight group (NWG) and an overweight/obese group (OG), based on anthropometric assessments.
The exclusion criteria were: children who had any type of infection, diabetes, and leukemia, as well as asthmatic bronchitis; those who were administered any drug that could interfere with salivary secretion (anticholinergics, neuroleptics, and benzodiazepines) at least 72 h before salivary collection; and those who refused to cooperate with data collection.
Sample size was based on a previous study by Modéer,et al. 3 (2011) on obesity and periodontal risk factors in adolescents. This was calculated at a 95% confidence interval and a study power of 80%. The OpenEpi software (http://www.openepi.com) was used, and a sample size of 52 children per group was calculated.
Short talks were held with the children's parents or guardians to explain the project and the importance of nutritional and dental assessment. Parents/guardians were interviewed to complete a medical history questionnaire, to identify possible health problems.
The research was carefully explained to the parents/ guardians of the participants, who signed a term of free, informed consent.
Specific days were scheduled the same week The standards adopted to classify children were based on the Lohman classification 16 ; from 11 to 20% children are classified as eutrophic; from 21 to 25%, as overweight; and above 25%, as obese. The circumference and skinfold measurements were used to confirm the BMI classification for children. Before saliva collection, the mouth was sanitized with distilled water, and the initial saliva was discarded before the stopwatch was used to determine salivary flow (mL/min).
The saliva was collected using a funnel into a 50 mL conical tube. Immediately after completing collection, the samples were stored on ice and transported in a styrofoam box to the salivary analysis laboratory.   in plasma and saliva, and have reported a good relationship between these variables. Thus, saliva collection is a valid, non-invasive method that is easy to perform and requires less pre-analysis handling, and as reduces the pain and anxiety that is typically associated with blood tests. 23 To our knowledge, this is the first study to   reported that gingivitis is prevalent in children and adolescents. 9 Gingival status should be accurately defined, to determine and control risk factors when assessing these data. Several  shows individuals with obesity have more gingivitis and more biofilm than the respective control group. 3,27 We believe that the differences between the literature and our results could be explained by the methodology of periodontal assessment (periodontal pocket probing and bone loss) and the age range of the individuals studied (10 to 17 years old).
The reduction in salivary flow is considered an important risk factor for periodontal diseases. 29 However, the salivary flow herein was considered normal, and no significant differences were observed between the groups. A previous study verified a correlation between salivary osmolality (which reflects the individual's hydration status) and gingival inflammation. 29 The authors reported that increased osmolality reduced salivary flow by increasing molecular cohesion, leading to increased risk of development of gingivitis. 30 A cross-sectional study demonstrated that individuals with obesity had significantly more gingival bleeding than the controls in adolescents. 6 In our study, although no differences were observed in gingival status among children of either group, the s-IgA values were statistically higher for the OG.