OBESITY AS A PROTECTIVE FACTOR FOR POSTMENOPAUSAL OSTEOPOROSIS

BACKGROUND: Obesity is considered a protective factor for osteoporosis improving bone mass and maintaining higher levels of estrogen during menopause. OBJECTIVE: To determine the association of obesity with bon e mineral density (BMD), and its relationship with sex hormone levels. DESIGN: A case-control study in Caucasian obese and non obese postmen opausal women. SUBJECTS: 113 obese and 50 non-obese postmenopausal wom en. MEASUREMENTS: BMD (dual-photon X-ray absorptiometry) at cervical f emur. Ward's triangle, proximal radius and lumbar spine. Plasma levels of glucose, insulin, total estrogen, follicle stimulating hormone (FS H), sex hormone binding globulin (SHBG), dehydroepiandrosterone sulfat e (DHA-S) and testosterone. RESULTS: Mean BMD at femoral sites were si gnificantly higher in obese women (femoral neck: 0.849 +/- 0.124 g/cm( 2) vs 0.753 +/- 0.095 g/cm(2), P < 0.001; Ward's triangle: 0.634 +/- 0 .134 g/cm(2) vs. 0.553 +/- 0.100 g/cm(2), P < 0.001). Mean BMD at lumb ar spine was 0.906 +/- 0.138 g/cm(2) in obese women and 0.849 +/- 0.13 7 g/cm(2) in non obese, P < 0.017. A decreased risk of osteopenia in f emoral neck (Age adjusted OR=0.36, 95%CI 0.17-0.75) and in lumbar spin e (Age adjusted OR=0.43, 95%CI 0.20-0.91) in obese women was observed. Although total estrogen were similar in both groups, in obese women, SHBG was lower (68.6 +/- 26.84 nmol/l vs. 85.1 +/- 31.18 nmol/l, Pt 0. 001), and postglucose load insulin levels were higher, than in non obe se (77.2 +/- 50.4 UI/ml vs. 49.4 +/- 24.1 UI/ml, P < 0.0005). CONCLUSI ON: The findings confirm a higher BMD in obese women and suggest that obesity exerts protection due to a decreased SHBG thus increasing free sex steroids. Besides, hyperinsulinemia may produce a decline in the production of IGFBG-1, leading to an increase of IGF-1, that may stimu late the proliferation of osteoblasts.