Regulation of bone mineral density in morbidly obese women: a cross-sectional study in two cohorts before and after bypass surgery.

Background: The mechanisms by which increased body weight influence bone mass density (BMD) are still unknown. The aim of our study was to analyze the relationship between anthropometric and body composition variables, insulin growth factor-I (IGF-I), adiponectin and soluble tumor necrosis factor-alpha receptors (sTNFR) 1 and 2 with BMD in two cohorts of morbid obese patients, before and after bypass surgery.

Methods: The first cohort included 25 women aged 48+/-7.6 years studied before bypass surgery. The second included 41 women aged 46+/-9.2 years, 12 months after surgery. We studied anthropometric variables obtained from whole body DEXA composition analysis. Serum IGF-I, intact serum parathyroid hormone, 25-hydroxivitamin D3, plasma adiponectin concentrations, sTNFR1, sTNFR2 concentrations were measured.

Results: In the first cohort, the BMI was 44.5+/-3.6 kg/m2, parathyroid hormone, IGF-I, and adiponectin concentrations were lower, and sTNFR1 concentrations were higher than in the second cohort. In the multiple regression analysis, BMD remained significantly associated with body fat percentage (beta -0.154, p=0.01), lean mass (beta 0.057, p=0.016) and phosphate concentration (beta 0.225, p=0.05). In the second cohort, BMI was 31+/-5.1 kg/m2. In the multiple regression analysis, BMD remained significantly associated with lean mass (beta 0.006, p=0.03).

Conclusion: The inverse correlation found between body fat and BMD in the first cohort indicates morbid obesity increases the risk of osteoporosis and we found a positive correlation with lean and fat mass before bariatric surgery and with lean mass after bypass surgery.