Association between obesity and flow rate of unstimulated whole saliva among elderly Koreans

Abstract

1. Objectives The prevalence of obesity continue to increase in all ages and ethnicities worldwide. Obesity is associated with increased risk of chronic inflammatory diseases such as type 2 diabet, atherosclerosis, cancer, and respiratory disorders. In addition, several studies have reported that obesity is related to several aspects of oral health, such as caries, periodontitis and dry mouth. There have been few studies on the relationship between obesity and hyposalivation. Moreover, very few studies on old ages have been found in the literature. Dry mouth is a common symptom in the older people that can produce serious negative effects on the patients quality of life. Although the increased prevalence of hyposalivation caused by diseases and intake of drugs in aged patients is well known, it is possible that obesity is also a determinant of dry mouth. Therefore, we performed this study to provide additional evidence of an association between obesity and salivary flow rate among Korean adults.

2. Methods In Korea, the Sun-Chang longevity cohort started in 2009. All 514 subjects (177 males and 337 females), selected from the Sun-Chang longevity cohort at baseline survey, participated voluntarily and provided written informed consent. Their ages ranged from 48 to 93 years, with a mean of 70.5 years. Unstimulated saliva was collected in a relaxed position and was passively drained for 10min into a test tube. We classify into 3 groups

those with very low SFR (UWSFR <0.1 ml/min)

those with low SFR (UWSFR = 0.1-0.19 ml/min)

and those who have normal SFR (UWSFR ≥ 0.2 ml/min). For evaluating obesity, trained examiners measured weight, height, hip circumference and waist circumference. Obesity was defined as a BMI ≥25kg/m2 and overweight was defined as a BMI between 23 and 25 kg/m2. Regarding WC, obesity was defined as a WC≥90cm for men and ≥85cm for women. Considering WHR, obesity was defined as a WHR≥0.90 for men and ≥0.80 for women. In order to obtain information about socio-demographic status, general health-related behaviors, the subjects were interviewed by a trained interviewer using structured questionnaires. To determine the strength of association and the dose-effect relationship between the salivary flow rate and the obesity indicator scores, analysis of covariance (ANCOVA) was performed. To determine the association between obesity and salivary flow rate, odds ratios with 95% confidence intervals were estimated by logistic regression analysis adjusting for age, gender, smoking, drinking, physical activity, number of teeth, denture wearing state, interaction of gender and obesity.

3. Results Unstimulated salivary flow rate ranged from 0.001ml/min to 0.968ml/min, with a mean of 0.13ml/min. Obesity is significantly correlated with age, gender, smoking, number of remained teeth, denture wearing state. We found that salivary flow rate significantly decreased with age and females had a lower flow rate than males. The people who smokes present and drinks 1-5 times monthly presented a significant higher salivary flow rate than non-smoker and non-drinking patients respectively. Physical activity, remained teeth and denture wearing state were not significantly correlated with salivary flow rate. In the analysis of covariance adjusted for age, gender, smoking, drinking, physical activity, number of teeth, denture wearing, none of the BMI, WC and WHR did not significantly correlated with salivary flow rate. In the multivariate logistic regression model adjusted for age, gender, smoking, drinking, physical activity, number of teeth, denture wearing, and interaction of obesity indices and gender, the prevalence of very low salivary flow rate in obese group was 11.5 times significantly higher than that of normal group (OR=11.54, 95% CI: 1.04-128.02). However, WC and WHR did not show the significant association with salivary flow rate. In conclusion, it is suggested that obesity may play a significant role in the control of salivary secretion, but the population bias to some of the rural elderly and obesity and salivary flow has been limited to less overall significant association. Further studies are needed to reappraise the interaction obesity and salivary flow rate in large and diverse population.