Research of the lipoprotein combined index and its association with osteoporosis in elderly Chinese adults: a retrospective cross-sectional study

Objective This study aimed to investigate the relationship between the lipoprotein combined index (LCI) and osteoporosis (OP) risk in elderly Chinese individuals. Methods This retrospective cross-sectional study included 7,383 participants aged 60 years and older who underwent chest computed tomography (CT) with quantitative CT (QCT) at the First Affiliated Hospital of the University of Science and Technology of China, Hefei, from January 2023 to June 2025. Participants were categorized into non-osteoporosis (non-OP) and osteoporosis (OP) groups based on lumbar spine bone mineral density (BMD), with BMD thresholds set at ≥ 80 mg/cm 3 for non-OP and < 80 mg/cm 3 for OP. The LCI was calculated using the following formula: (total cholesterol × triglycerides × low-density lipoprotein cholesterol (LDL-C))/high-density lipoprotein cholesterol (HDL-C), and was divided into quartiles (Q1–Q4). Multivariate logistic regression, restricted cubic spline (RCS) plots, and subgroup analyses were used to assess the relationship between LCI and OP. Results LCI levels were significantly lower in the OP group compared to the non-OP group ( P < 0.001). After multivariate adjustment, higher LCI levels were inversely associated with OP risk (OR = 0.993, 95% CI [0.990–0.997], P < 0.001). Specifically, individuals in the Q4 group had a 19.3% lower risk of OP than those in the Q1 group (OR = 0.807, 95% CI [0.681–0.956], P = 0.013). RCS analysis revealed a nonlinear relationship ( P = 0.048), with a threshold effect at an LCI of 18; below this threshold, no significant correlation was found, whereas above it, each unit increase in LCI was associated with a 1.0% reduction in risk. Subgroup analysis indicated that the inverse association of LCI was more pronounced in participants without a history of cerebral infarction ( P for interaction = 0.003). Conclusion Higher LCI levels are independently linked to a reduced risk of OP in older adults, particularly when LCI ≥ 18. LCI may serve as a potential biomarker reflecting the role of lipid metabolism in OP.