Does obesity cause periodontitis? A single-mediation analysis

Objectives: Obesity and periodontitis are chronic co-morbidities that share common risk factors and have a significant public health impact in Australia. This study aimed to determine the causal relationship between obesity and periodontitis in Australian adults.

Methods: A subset of 3715 participants, 30 years and older were selected for the secondary analysis from the National Survey of Adult Oral Health 2004-06. A direct acyclic graph was constructed to display the relationship between obesity and periodontitis. Dental visiting behaviour (a de facto measure of healthy behaviours) was considered as a mediator between obesity and periodontitis. The confounding variables include demographic factors (age and sex), socioeconomic position (household income and education), and health and lifestyle factors; (diabetes, alcohol intake, smoking status). Obesity was defined as physical inactivity induced obesity (BMI more than 25kg/m2 and no moderate physical activity). Single mediation analysis was used to decompose the total causal effect of obesity on periodontitis into its direct and indirect effects using the potential outcome approach. This was done in STATA version 15, using causal mediation analysis using the paramed library. Sensitivity analysis was conducted to verify the presence of unmeasured confounding between exposure and outcome using the E-value estimate. Data from the National Survey of Adult Oral Health, Australia, 2004-2006 was used to conduct this analysis.

Results: The total causal effect of obesity to periodontitis was 14%. Pathway effect analysis using potential outcomes illustrate that the effect of obesity on periodontitis which was not mediated through poor dental visiting behaviour was 13%. The indirect effect, the effect of obesity-mediated through poor dental visiting behaviour on periodontitis, was 1%.

Conclusions: The direct effect of obesity on periodontitis was higher than the indirect effect of obesity on periodontitis through poor dental visiting behaviour.