Association Between Weight-Adjusted Waist Index (WWI) and Bone Mineral Density in Postmenopausal Women: A Cross-Sectional Analysis of NHANES Data.

Background: Osteoporosis represents a critical public health challenge, particularly among postmenopausal women, characterized by reduced bone mineral density (BMD) and increased fracture risk. Traditional obesity metrics such as body mass index (BMI) and waist circumference (WC) have limitations in assessing bone health due to their inability to differentiate lean and fat mass. The weight-adjusted waist index (WWI), a novel anthropometric indicator, offers a more nuanced approach to evaluating body composition and metabolic risks. Objective: The WWI is a novel obesity metric that demonstrates superior accuracy in evaluating both muscle mass and adiposity compared to conventional anthropometric measurements. This cross-sectional study examined the relationship between WWI and BMD at the femoral neck in a nationally representative sample of American postmenopausal women. Methods: A cross-sectional analysis was conducted using data from the National Health and Nutrition Examination Survey (NHANES), including 3198 postmenopausal women aged 40 and older. WWI was calculated by dividing WC by the square root of body weight. BMD was assessed using dual-energy X-ray absorptiometry (DXA). Multivariate regression analyses were performed, adjusting for potential confounders including age, race, height, BMI, and metabolic markers. Results: Multiple regression analyses revealed a significant negative correlation between WWI and femoral neck BMD. A critical threshold of 10.32 was identified, beyond which the relationship with BMD shifted. Below this threshold, higher WWI levels showed a protective effect on BMD (β = 0.03, p=0.0265), while above the threshold, WWI exhibited a significant negative influence (β = -0.01, p < 0.0001). Stratified analyses demonstrated variations in the WWI-BMD relationship across different subgroups, including age, race, and menopause status. Conclusion: This cross-sectional analysis revealed a significant negative correlation between the WWI and femoral neck BMD in a nationally representative cohort of American postmenopausal women. Notably, the association demonstrated a nonlinear inverted U-shaped pattern with an identifiable threshold effect.