Association between a body shape index and cardiometabolic multimorbidity: a parallel analysis of middle-aged and older adults in China and the United States

The prevalence of cardiometabolic multimorbidity (CMM) continues to rise among middle-aged and older populations, with central adiposity increasingly recognized as a major contributing factor. A Body Shape Index (ABSI), a relatively new metric describing physical form, shows an uncertain relationship with CMM. This investigation sought to evaluate how ABSI relates to CMM in middle-aged and older cohorts drawn from both China and the United States. Data analyzed in this study were obtained via two major national databases: the China Health and Retirement Longitudinal Study (CHARLS, n = 13,128) and the U.S. National Health and Nutrition Examination Survey (NHANES, n = 13,506), covering the years 2011 and 2011–2022, respectively. Weighted logistic regression was used to assess the associations between ABSI and CMM, as well as between ABSI and individual cardiometabolic conditions. Restricted cubic spline (RCS) analyses and subgroup analyses were conducted to further explore the dose–response relationships and population-specific differences. In both the CHARLS and NHANES datasets, among adults aged ≥ 65 years, the prevalence of CMM was significantly higher than in younger age groups in both the CHARLS and NHANES datasets. Overall, ABSI showed a positive association with CMM. In the Model 3, participants in the highest ABSI quartile had a 27% higher odds of CMM in CHARLS (OR = 1.27, 95% CI: 1.07–1.51) and a 59% higher odds in NHANES (OR = 1.59, 95% CI: 1.38–1.84), compared to those in the lowest quartile; both trends were statistically significant (P-trend < 0.05). Disease-specific analyses indicated that ABSI was significantly associated with both diabetes and hypertension, with consistent patterns observed across both populations. RCS analysis further revealed a significant nonlinear relationship between ABSI and CMM. Subgroup analyses showed that the association was more pronounced among individuals aged 45–65 years and among males. ABSI shows a significant correlation with CMM among mid-aged and older individuals in both China and the U.S. These findings suggest that ABSI may serve as a useful complementary metric for identifying at-risk individuals and guiding health management in aging populations.