Purpose: To investigate associations between body mass index (BMI), body fat percentage, and components of sarcopenia (muscle mass and muscle strength/power), with bone microarchitecture measured by high-resolution peripheral computed tomography (HR-pQCT) in older adults with obesity.
Methods: Seventy-four adults aged ≥55 years with body fat percentage ≥30% (men) or ≥40% (women) were included. Fat mass, lean mass and total hip, femoral neck, and lumbar spine areal bone mineral density (aBMD) were measured by dual-energy X-ray absorptiometry. Appendicular lean mass (ALM) was calculated as the sum of lean mass in the upper- and lower-limbs. BMI was calculated and participants completed physical function assessments including stair climb power test. Distal tibial bone microarchitecture was assessed using HR-pQCT. Linear regression (β-coefficients and 95% confidence intervals) analyses were performed with adjustment for confounders including age, sex, smoking status, vitamin D and self-reported moderate to vigorous physical activity.
Results: BMI and ALM were both positively associated with total hip, femoral neck and lumbar spine aBMD and trabecular bone parameters including bone volume fraction and volumetric BMD (vBMD) after adjusting for confounders (all p<0.05). Body fat percentage was not associated with aBMD or any trabecular bone parameters but was negatively associated with cortical area (-1.647mm2; -3.127, -0.167). Stair climb power (indicating better performance) was positively associated with cortical area and bone stiffness (both p<0.05).
Conclusion: Higher BMI, ALM and muscle power were associated with more favourable bone microarchitecture, but higher body fat percentage was negatively associated with cortical bone area. These findings suggest the protective effect of high BMI for fractures is attributable to higher muscle mass and/or forces, but that higher relative body fat is not associated with/beneficial for bone health in older adults with obesity.