Identification of Dampness Constitution Based on Bioimpedance Analysis: Independent Associations Between Extracellular Fluid and Trunk Reactance.

This study aimed to identify objective bioelectrical impedance analysis (BIA) parameters independently associated with the dampness constitution (phlegm-dampness and damp-heat constitutions) in Traditional Chinese Medicine (TCM), thereby providing candidate indicators for its objective identification. In this cross-sectional study, 232 participants (129 with the Harmonious constitution and 103 with the dampness constitution) were consecutively recruited from a community-based health screening program. Whole-body and segmental fluid distribution, bioelectrical parameters, and grip strength were measured. Core features were identified using Least Absolute Shrinkage and Selection Operator (LASSO) regression, and their independent associations with the dampness constitution were assessed using multivariable logistic regression; sex-stratified and sensitivity analyses (Winsorization and additional adjustment for waist-to-hip ratio or abdominal circumference) were also performed. LASSO identified five core features: left lower limb phase angle (PA_LL), trunk reactance (Reactance_TR), extracellular water (ECW), body fat percentage (PBF), and mean grip strength. In the multivariable model, ECW (OR = 1.307, 95% CI: 1.046-1.649, p = 0.021) and Reactance_TR (OR = 2.163, 95% CI: 1.124-4.267, p = 0.023) were independently and positively associated with the dampness constitution. In sex-stratified analyses, both associations were statistically significant in men (ECW: OR = 1.407, p = 0.038; Reactance_TR: OR = 2.764, p = 0.030) but not in women. Formal interaction testing did not support a statistically significant sex difference (sex × ECW: p = 0.573; sex × Reactance_TR: p = 0.605), suggesting that the apparent sex difference may reflect lower statistical power in the smaller female subgroup. The associations remained stable in all sensitivity analyses. In conclusion, ECW and Reactance_TR are two core BIA indices independently associated with the dampness constitution, suggesting trunk fluid retention and altered bioelectrical properties in affected individuals. These parameters constitute preliminary candidate indicators for the objective identification of the dampness constitution and require validation in independent populations.