The association between cardiac metabolic index and lumbar bone mineral density in adults: NHANES 2011-2018

Abstract Introduction: The association between cardiovascular disease (CVD) and bone metabolism has been extensively investigated. The cardiac metabolic index (CMI) is a new indicator of cardiovascular metabolism. Our study aimed to explore the relationship between CMI and lumbar bone mineral density (BMD) in adults. Methods This population-based study investigated the relationship between CMI and lumbar BMD in adults, using data from the National Health and Nutrition Examination Survey (NHANES) 2011–2018. CMI is computed as the conduct of TG(Triglyceride) (mmol/L)/HDL-C(high-density lipoprotein cholesterol)(mmol/L) ratio and waist(cm)/height(cm) ratio (WHtR). Weighted multivariate linear regression and smoothed curve fitting were employed to examine linear and non-linear associations between CMI and lumbar BMD. Threshold effects were determined using a two-part linear regression model. Additionally, subgroup analyses and interaction tests were conducted to assess the stability of the relationship between CMI and lumbar BMD in different demographic contexts. Results Multivariate linear regression analysis revealed a significant negative association between CMI and lumbar BMD [β = −0.01, 95% CI: −0.02, − 0.01]. This negative correlation remained consistent across all subgroups, encompassing age, gender, ethnicity, and diabetes status. Furthermore, a U-shaped relationship between CMI and lumbar BMD was observed, with an inflection point of 1.26 (log likelihood ratio < 0.01). When CMI was less than 1.26, the association between CMI and lumbar BMD was negative [β=-0.03, 95% CI= (-0.05, -0.02)], while when CMI was greater than 1.26, the association between CMI and lumbar BMD was positive [β = 0.02, 95% CI= (-0.01,0.05)]. Conclusions In adults, there is a negative association between CMI and lumbar BMD.