Salivary profiles in relation to oral health and adiposity status among adolescents

Abstract

Oral diseases (dental caries and poor periodontal health) and obesity are ongoing public health concerns. Although the relationship between oral health and obesity has been extensively explored in epidemiological studies, the underlying mechanism is not fully understood. This study aimed to: 1) systematically evaluate the association of salivary profiles with oral health and obesity and 2) investigate the triadic association between salivary profiles, oral health, and obesity among Hong Kong adolescents. Two systematic reviews were conducted to investigate the association of salivary profiles with oral health (caries status and periodontal health) and/or obesity. Adiposity indices, caries experience, periodontal status, salivary physicochemical parameters, sociodemographic status, and oral health behaviours were obtained from a random sample of Hong Kong adolescents aged 12–15 years. Laboratory measurements of salivary protein biomarkers and bacteria were performed. The first systematic review demonstrated that individuals with dental caries and/or obesity had altered salivary profiles, with very-low-quality evidence. In our age- and sex-matched sample (n = 180), adolescents with a high waist-to-height ratio (WHtR), dental caries, or the coexistence of these two conditions had significantly higher salivary lipoprotein-associated phospholipase A2 (Lp-PLA2) concentrations and lower stimulated salivary flow rates than caries-free controls with a normal WHtR. Among adolescents with dental caries, those with a high WHtR had significantly lower salivary secretory phospholipase A2 group IIA (sPLA2-IIA) output and higher total salivary bacterial load than those with a normal WHtR. Logistic regression analysis demonstrated that adolescents with general overweight/obesity (odds ratio [OR] = 3.33, 95% confidence interval [CI]: 1.28–8.65) and those with central obesity (OR = 2.47, 95% CI: 1.02–6.00) had a significantly greater chance of having a high salivary abundance of Streptococcus mutans (> 1E+6 colony-forming units/mL) after adjusting for sociodemographic factors and oral health behaviours. Our findings suggest that both dental caries and central obesity are associated with elevated salivary Lp-PLA2 concentration and decreased salivary gland secretory function. Adolescents with coexisting dental caries and central obesity are likely to have a weakened salivary defence. General overweight/obesity and central obesity were associated with a higher salivary abundance of S. mutans. No study in the second systematic review adequately addressed the triadic association between salivary biomarkers, periodontal status, and obesity among children and adolescents. Our cross-sectional study of 714 adolescents demonstrated that adolescents with a higher trunk body fat percentage or WHtR; higher pH or buffering capacity in stimulated whole saliva; higher visible plaque index value; or who were male, older, or brushed their teeth less than twice daily had a higher risk of having calculus. Among participants with a normal WHtR in our random sample of 180 adolescents, those with more extensive periodontal inflammation had significantly elevated salivary interleukin-6 output than those with less extensive periodontal inflammation. Salivary interleukin-6 concentrations were negatively correlated with the number of sextants with healthy gingivae and positively correlated with salivary sPLA2-IIA concentrations. However, these findings were not observed in adolescents with a high WHtR. Adolescents with different adiposity status may have different mechanisms for periodontal inflammation, but this needs further investigation.