# The saturation effect of a body shape index on lumbar bone mineral density in US adults: Findings from a nationwide survey

## TL;DR

This study finds that higher body shape index is linked to lower lumbar bone density in US adults, with a saturation effect at a specific index value.

## Contribution

The study identifies a nonlinear saturation effect between body shape index and lumbar bone mineral density, a novel observation in obesity-bone health research.

## Key findings

- ABSI is negatively correlated with lumbar BMD (β = -0.007) in a nationwide US sample.
- A saturation effect is observed at an ABSI value of 0.08, beyond which the negative impact plateaus.
- The nonlinear relationship holds across subgroups including age, gender, race, and BMI categories.

## Abstract

Many studies have demonstrated that obesity is closely linked with bone metabolism. A body shape index (ABSI) is a newly developed obesity indicator, which provides superior reflection of central obesity compared to body mass index (BMI) and waist circumference. Nevertheless, investigation of the association between ABSI and bone mineral density (BMD) remains limited. Thus, this study aimed to evaluate the correlation between ABSI and lumbar BMD among US adults.

We analyzed data of adults aged 20 years and older from 2011–2018 National Health and Nutrition Examination Survey. Weighted multiple regression analysis was conducted to assess the linear relationship between ABSI and lumbar BMD. Weighted smooth curve fitting and two-segment linear model were applied to explore the nonlinear association. Subgroup analysis stratified by age, gender, race, and BMI was performed.

A total of 10991 subjects was enrolled in the study. In the fully adjusted model, the ABSI was negatively related to lumbar BMD (β = −0.007, 95% CI: −0.009, −0.005). The adverse correlation remained significant across all subgroups among stratified analysis. The saturation effect between ABSI and lumbar BMD was identified, with the turning point at the ABSI value of 0.08. Similar nonlinear trends were also observed in participants aged <40 years, males, Non-Hispanic White, BMI < 25 kg/m2, and BMI ≥ 30 kg/m2.

This study revealed a prominently negative correlation and saturation effect between ABSI and lumbar BMD in US adults. Our findings may provide valuable inspiration for further prevention and intervention of osteoporosis.