Influence of lean and fat mass on bone mineral density (BMD) in postmenopausal women with osteoporosis

Despite known positive association between body mass and bone mineral density (BMD), relative contribution of fat and lean tissue to BMD remains under debate. We aimed at investigating the effect of selected anthropometric parameters, including fat content and lean body mass (LBM) on BMD in postmenopausal, osteoporotic women with body mass index (BMI) > 20 kg/m2. The study involved 92 never-treated women (mean age 69.5 ± 7.3). L1–L4 and femoral neck (FN) BMD were measured by dual energy X-ray absorptiometry (DEXA). Absolute (kg) and relative (%) fat and LBM were assessed by means of electric bioimpedance method. We showed both FN and L1–L4 BMD were positively correlated with body mass, waist circumference (WC), hip circumference (HC) and LBM (kg). Fat content correlated with FN BMD (r = 0.36, p < 0.001). Regression analysis revealed the only predictor of L1–L4 BMD was LBM (R2 = 0.18, p < 0.05), for FN – both LBM and fat (R2 = 0.18, p < 0.05 and p < 0.001, respectively). Of the women, 44.5% were overweight, 18.4% obese. Obese women displayed the highest BMD. Both L1–L4 and FN BMD were higher in women with WC > 80 cm. In postmenopausal osteoporotic women with BMI > 20 kg/m2 both fat and lean tissue might contribute to BMD. Positive association between body mass and BMD does not make obesity and osteoporosis mutually exclusive.