Associations between bone mass, hormone levels, and body composition in postmenopausal women

The aim of this study was to explore body composition parameters and hormone levels as risk factors for low bone mass (osteopenia/osteoporosis) in postmenopausal women.We analyzed biorepository samples from 139 postmenopausal women with no clinical evidence of cardiovascular disease. Inclusion criteria were menopause occurring after 40 years of age and no use of hormone therapy in the past 3 months. Bone mineral density and body composition were assessed by dual-energy x-ray absorptiometry. Sex hormone-binding globulin (SHBG) and follicle-stimulating hormone (FSH) levels were measured in all participants. Serum estradiol was measured by gas chromatography/tandem mass spectrometry in a subset of 57 participants. Free estrogen index was calculated by dividing estradiol by SHBG × 100.Body mass index (25.0 [22.5-26.5] vs 27.7 [26.6-31.9] kg/m 2 , P < 0.001), estradiol (3.0 [2.7-4.5] vs 6.0 [2.7-15.0] pg/mL, P = 0.006), waist circumference (84 ± 9 vs 93 ± 12 cm, P < 0.001), appendicular lean mass (ALM) (15.739 ± 2.129 vs 17.184 ± 2.104 kg, P = 0.001), and fat mass index (9.36 [7.29-11.43] vs 11.38 [9.95-15.33] kg/m 2 , P < 0.001) were lower in women with low bone mass by dual-energy x-ray absorptiometry. Univariate analysis showed that free estrogen index, time since menopause, SHBG, and fat mass were significant predictors of low bone mass, and ALM was a significant predictor against low bone mass. Appendicular lean mass persisted as an independent predictor against low bone mass in multivariate models with fat mass and SHBG. In turn, fat mass was no longer significant in this multivariate model after inclusion of SHBG. No association of FSH with low bone mass was observed.Appendicular lean mass was a significant independent predictor against low bone mass in postmenopausal women. Further prospective studies are needed to investigate whether lean mass, fat mass, and FSH have a direct effect on bone mass in postmenopausal women, adding to the consequences of hypoestrogenism in this group.