TY - JOUR

T1 - Association of a Combined Body Mass Index and Regional Body Fat Percentage Metric With Fragility Fracture Risk

T2 - Evidence from a Large Observational Cohort

AU - Amin, Hamzah

AU - Swainson, Michelle G.

AU - Khan, Muhammed Aqib

AU - Bukhari, Marwan

PY - 2025/4/30

Y1 - 2025/4/30

N2 - Background: Evidence suggests that high body fat and low muscle mass may increase the risk of fragility fractures. However, current fracture risk models, which largely rely on body mass index (BMI), may not fully capture these compositional factors. We recommend integrating additional body composition variables into fracture risk calculators to improve accuracy. Previously, we described partial body fat percentage (PBF%), a novel measure that is routinely available and calculated as the proportion of fat at the lumbar spine and hip during DXA scans. We hypothesize that a combined BMI and PBF% approach (BMI/PBF%) could be associated with fragility fracture. Methods: Patients were referred to our DXA scanner between June 2004 and February 2024 and had combined lumbar spine and bilateral femoral scans. Patients were initially categorized by BMI (underweight, normal weight, overweight and obese) and then divided into tertiles of PBF%. Based on each patient's unique combination of BMI and PBF% tertile, they were stratified into 12 binary BMI/PBF% groups for analysis. Multivariable logistic regression models, reporting odds ratios (OR), with BMI/PBF% groups as the independent variables and fragility fractures as the dependent variable were fit, with all results adjusted for known fracture risk factors. Results: We analysed 36 235 patients (83.4% female, 16.6% male), of whom 14 342 (39.5%) reported fragility fractures. The median (IQR) age was 67.7 (57.5–75.0) years, with a BMI of 26.4 (23.3–30.2) kg/m2 and PBF% of 30.6% (25.5% – 35.4%). In females, those in the lowest PBF% tertile had reduced odds of fragility fractures across all BMI categories (e.g., obese low PBF%: OR 0.70, 95% CI 0.64–0.78), whereas in males, this reduction was observed only amongst overweight and obese individuals (e.g., obese low PBF%: OR 0.71, 95% CI 0.57–0.88). No association was found for patients in the middle PBF% tertile across any BMI group. In contrast, females in the highest PBF% tertile exhibited increased odds of fractures across all BMI categories except underweight (e.g., obese high PBF%: OR 1.31, 95% CI 1.22–1.42), and a similar pattern was seen in males, but limited to the overweight and obese groups (e.g., obese high PBF%: OR 1.27, 95% CI 1.04–1.55). Conclusion: High or low PBF% within BMI categories is associated with fragility fractures, challenging the traditional notion that high BMI protects against fractures. This study highlights the importance of body composition measures beyond BMI in fracture risk assessment.

AB - Background: Evidence suggests that high body fat and low muscle mass may increase the risk of fragility fractures. However, current fracture risk models, which largely rely on body mass index (BMI), may not fully capture these compositional factors. We recommend integrating additional body composition variables into fracture risk calculators to improve accuracy. Previously, we described partial body fat percentage (PBF%), a novel measure that is routinely available and calculated as the proportion of fat at the lumbar spine and hip during DXA scans. We hypothesize that a combined BMI and PBF% approach (BMI/PBF%) could be associated with fragility fracture. Methods: Patients were referred to our DXA scanner between June 2004 and February 2024 and had combined lumbar spine and bilateral femoral scans. Patients were initially categorized by BMI (underweight, normal weight, overweight and obese) and then divided into tertiles of PBF%. Based on each patient's unique combination of BMI and PBF% tertile, they were stratified into 12 binary BMI/PBF% groups for analysis. Multivariable logistic regression models, reporting odds ratios (OR), with BMI/PBF% groups as the independent variables and fragility fractures as the dependent variable were fit, with all results adjusted for known fracture risk factors. Results: We analysed 36 235 patients (83.4% female, 16.6% male), of whom 14 342 (39.5%) reported fragility fractures. The median (IQR) age was 67.7 (57.5–75.0) years, with a BMI of 26.4 (23.3–30.2) kg/m2 and PBF% of 30.6% (25.5% – 35.4%). In females, those in the lowest PBF% tertile had reduced odds of fragility fractures across all BMI categories (e.g., obese low PBF%: OR 0.70, 95% CI 0.64–0.78), whereas in males, this reduction was observed only amongst overweight and obese individuals (e.g., obese low PBF%: OR 0.71, 95% CI 0.57–0.88). No association was found for patients in the middle PBF% tertile across any BMI group. In contrast, females in the highest PBF% tertile exhibited increased odds of fractures across all BMI categories except underweight (e.g., obese high PBF%: OR 1.31, 95% CI 1.22–1.42), and a similar pattern was seen in males, but limited to the overweight and obese groups (e.g., obese high PBF%: OR 1.27, 95% CI 1.04–1.55). Conclusion: High or low PBF% within BMI categories is associated with fragility fractures, challenging the traditional notion that high BMI protects against fractures. This study highlights the importance of body composition measures beyond BMI in fracture risk assessment.

KW - sarcopenic obesity

KW - BMI

KW - obesity

KW - fragility fractures

KW - sarcopenia

KW - fracture risk estimation

KW - body composition

KW - ageing population

KW - adiposity

U2 - 10.1002/jcsm.13808

DO - 10.1002/jcsm.13808

M3 - Journal article

VL - 16

JO - Journal of Cachexia, Sarcopenia and Muscle

JF - Journal of Cachexia, Sarcopenia and Muscle

SN - 2190-5991

IS - 2

M1 - e13808

ER -