Association between body mass index, bone bending strength, and BMD in young sedentary women

Abstract

The rationale was to determine whether body mass index (BMI) is a predictor of bone bending strength and bone mineral density (BMD) in young sedentary women. Results show that BMI is not a predictor of bone bending strength and that young women with low BMI also have low BMD. The purpose of this study was to determine whether body mass index (BMI) is a predictor of tibial or ulnar bending strength and bone mineral density (BMD) in sedentary women. Sedentary women (n\u2009=\u200934), age 19–27 years, with low BMI (LBMI\u2009<\u200918.5 kg/m2, n\u2009=\u200916), and normal or high BMI (NHBMI between 18.5 and 29.9 kg/m2, n\u2009=\u200918) participated as study subjects. Study outcomes included tibial and ulnar bending strength (EI in Nm2) using a non-invasive mechanical response tissue analyzer (MRTA); BMD and bone mineral content (BMC) of the whole body (WB), femoral neck (FN), total hip (TH), lumbar spine 1–4 (LS1–4), and ulna; and bone turnover biomarkers. The LBMI group have lower (p\u2009<\u20090.01) body weight [group difference (Δ)\u2009=\u200932.0%], lean mass (LM) (Δ\u2009=\u200923.1%), fat mass (FM) (Δ\u2009=\u200977.2%), and tibial bending strength (Δ\u2009=\u200922.0%), compared to the NHBMI. The LBMI group also have lower (all p\u2009<\u20090.025) BMC in WB (Δ\u2009=\u200919.9%), FN (Δ\u2009=\u200920.1%) and TH (Δ\u2009=\u200919.0%), compared to the NHMBI, not in BMD results. Multivariate regression analysis shows that significant predictors of tibial bending strength are tibia length (adjusted R2\u2009=\u2009.341), age (adjusted R2\u2009=\u2009.489), ulna BMD (adjusted R2\u2009=\u2009.536), and LM (adjusted R2\u2009=\u2009.580). BMI was positively correlated with tibial EI (p\u2009<\u20090.05), height, weight, FM, LM, body fat% (all p\u2009<\u20090.01), and BMD of WB, FN, TH, and LS 1–4 (p\u2009<\u20090.05 or\u2009<\u20090.01). Our results show that BMI is not a significant predictor of tibial or ulnar bending strength in young sedentary women.