Saturation Effect of Lipid Accumulation Product (LAP) Index on Spinal Bone Mineral Density: A Population-Based Study

Lipid accumulation product (LAP) has a positive effect on spinal bone mineral density (BMD). However, once LAP levels exceed 27.26, the rate of spinal BMD increase slow down or even decline. This indicates a biphasic relationship between lipid metabolism and BMD, suggesting potential benefits within a certain range and possible adverse effects beyond that range. This study aimed to investigate the potential association between LAP index and BMD in US adults, as well as to explore the presence of a potential saturation effect in this relationship. This study analyzed data from the National Health and Nutrition Examination Survey (NHANES) spanning from 2007 to 2018. A multiple stepwise regression model was employed to examine the association between LAP index and total spinal BMD. Additionally, a generalized additive model and a smooth curve fitting algorithm were utilized to examine the relationship, and saturation effect study was conducted to determine the saturation level. The calculation formula of LAP used in the study was: (LAP = (waist circumstances (WC) (cm) - 58) × triglyceride (TG) (mmol/L)) for women, and (LAP = (WC (cm) - 65) × TG (mmol/L)) for men. The study involved a total of 7913 participants aged 20 years or older. Through multiple stepwise regression analysis, it was found that individuals with higher LAP scores exhibited higher total spinal BMD. In both the crude and partially adjusted models, total spinal BMD was significantly higher in the highest LAP quartile (Q4) compared to the lowest LAP quartile (Q1) (P < 0.05). Utilizing a generalized additive model and smooth curve, a nonlinear relationship between LAP and total spinal BMD was observed. Furthermore, the study identified the saturation value of LAP to be 27.26, indicating a saturation effect. This research highlights a nonlinear relationship between LAP and total spinal BMD, along with the presence of a saturation effect.