Association and discriminative performance of relative fat mass for frailty index in US older adultsoxy_comment_end

This study aims to examine the association between Relative Fat Mass (RFM) and the frailty index (FI) among U.S. adults aged 60 years and older, and to assess the discriminative performance of RFM for high FI status. Utilizing NHANES data from 2007 to 2018, RFM was calculated using the formula RFM = 64 - (20 × height/wc) + (12 × sex), where female sex is assigned a value of 1 and male sex a value of 0. The degree of frailty was assessed using the FI based on the Rockwood cumulative deficit model, and an FI ≥ 0.25 was defined as frailty. To investigate the relationship between RFM and the occurrence of high FI, weighted multivariate logistic regression analysis, subgroup analyses, and interaction tests were conducted. Generalized additive modeling (GAM) was applied to account for any non-linear patterns, and receiver operating characteristic (ROC) analysis was utilized to evaluate RFM's discriminative capacity for high FI. The prevalence of high FI increased by 12% for each unit increase in RFM in a fully adjusted model, indicating a significant and positive relationship between RFM and high FI prevalence (OR: 1.12, 95% CI: 1.10, 1.15; P < 0.0001). RFM and the prevalence of high FI exhibited a substantial association across the majority of categories. Additionally, no statistically significant interactions were identified in most subgroups. The threshold effect and non-linear relationship were significant in the GAM model. RFM demonstrated superior discriminative performance for the prevalence of high FI compared to BMI and WC across all populations. This study suggests that elevated RFM is significantly associated with the development of high FI in older adults; however, further validation is warranted in a large prospective study.