Association between conicity index and osteoporosis/femoral bone mineral density in USA adults : a cross-sectional study based on evidence from the National Health and Nutrition Examination Survey (2005 to 2020).

AIMS: Osteoporosis poses a substantial public health burden. The conicity index (C-index), which integrates waist circumference, weight, and height, is a validated measure of abdominal obesity. However, its association with osteoporosis and femoral bone mineral density (BMD) remains unclear.

METHODS

This study analyzed data from 16,218 USA adults (aged ≥ 20 years) in the 2005 to 2020 National Health and Nutrition Examination Survey (NHANES). Associations between C-index and osteoporosis were assessed by weighted multivariable logistic regression, while associations between C-index and femoral BMD (total femur, neck, trochanter, intertrochanter) were evaluated by weighted multivariable linear regression. Potential non-linearity was explored via generalized additive models with smooth curve fitting. Threshold effect and dose-response analyses were performed, and robustness was tested by subgroup analyses.

RESULTS

After full adjustment for confounders, participants in the highest C-index quartile (Q4) had significantly higher odds of osteoporosis than those in the lowest quartile (Q1) (OR 1.67 (95% CI 1.23 to 2.27); p = 0.001). Each one-unit increase in C-index was associated with statistically significant decreases in BMD, as follows: total femur (-0.17 g/cm2), femoral neck (-0.18 g/cm2), trochanter (-0.17 g/cm2), and intertrochanter (-0.18 g/cm2). These associations persisted in subgroup analyses. A non-linear relationship was identified between C-index and femoral BMD.

CONCLUSION

Elevated C-index independently predicts osteoporosis risk and femoral BMD reduction in USA adults, with critical thresholds indicating accelerated bone loss. It thus serves as a clinically actionable metric for osteoporosis risk stratification in abdominal obesity management.