Association between systemic inflammation and overactive bladder: The potential mediating role of obesity-related...

Systemic inflammation is increasingly implicated in the development of chronic diseases, yet the specific association between the Aggregate Index of Systemic Inflammation (AISI) - a novel composite inflammatory marker - and overactive bladder (OAB) remains poorly understood. This study aimed to elucidate the association between AISI levels and OAB prevalence and to explore the statistical mediating effect of anthropometric indicators within the potential inflammation-metabolism pathway. This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) 2009-2018, including 18,601 participants aged ≥ 20 years. Weighted multivariate logistic regression and smooth curve fitting were employed to evaluate the association between the logarithmic AISI (LN-AISI) and OAB. Subgroup analyses and interaction tests were conducted to assess robustness. Furthermore, an exploratory statistical mediation analysis was performed to quantify the extent to which body mass index (BMI), relative fat mass (RFM), weight-adjusted-waist index (WWI), and body roundness index (BRI) statistically mediate this association. Participants in the highest quartile of LN-AISI exhibited 21% higher odds of OAB compared to the lowest quartile (OR 1.21, 95% CI: 1.02-1.44, P = .0349) after adjusting for covariates. Smooth curve fitting revealed a nonlinear dose-response relationship; notably, above a data-driven threshold of LN-AISI > 5.71, each unit increase was associated with 50% higher odds of OAB (OR 1.50, 95% CI: 1.32-1.70, P < .0001). This association was consistent across most subgroups but modified by age. Mediation analysis suggested that anthropometric indicators statistically mediated the AISI-OAB association, with mediation proportions of 31.3% for BMI, 36.2% for RFM, 26.4% for WWI, and 37.1% for BRI. Elevated AISI is associated with higher odds of OAB in a nonlinear, dose-dependent manner, particularly among older adults. Obesity-related anthropometric indices appear to statistically mediate this association in our cross-sectional sample. These findings suggest that managing systemic inflammation and body weight may represent associated factors worth exploring in future preventive research on OAB. However, given the cross-sectional design, these results represent statistical associations rather than confirmed causal mechanisms, warranting further longitudinal validation.