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Title: The Soy Isoflavones to Reduce Bone Loss (SIRBL) Study: Three Year Effects on pQCT Bone Mineral Density and Strength Measures in Postmenopausal Women

Author
item Shedd-wise, Kristine - University Of California
item Alekel, Lee - Iowa State University
item Hofmann, Heikke - Iowa State University
item Hanson, Kathy - Iowa State University
item Schiferl, Dan - Bone Diagnostics, Inc
item Van Loan, Marta

Submitted to: Journal of Clinical Densitometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2010
Publication Date: 2/3/2011
Publication URL: http://www.sciencedirect.com/science/article/pii/S109469501000288X
Citation: Shedd-Wise, K.M., Alekel, L.D., Hofmann, H., Hanson, K.B., Schiferl, D.J., Van Loan, M.D. 2011. The Soy Isoflavones to Reduce Bone Loss (SIRBL) Study: Three Year Effects on pQCT Bone Mineral Density and Strength Measures in Postmenopausal Women. Journal of Clinical Densitometry. doi: 10.1016/j.joed.2010.11.003.

Interpretive Summary: Osteoporosis is a disease of aging, found primarily in postmenopausal women. Soy isoflavones are believed to reduce age related bone loss in postmenopausal women because the chemical structure of soy isoflavones look like human estrogen. Therefore, we examined the effect of soy isoflavones, 2 doses: 80 mg/d and 120 mg/d, on bone density and strength parameters following 3-yrs. of soy isoflavone treatment. Bone density and strength measurements were made on the thigh bone of each woman and showed that as time since menopause increased the 120 mg/d dose was protective of cortical bone density. We also found that soy isoflavones were generally negative predictors of bone strength, but the 80 mg/d dose became more protective as bone metabolism (rates of formation and resorption) increased. Overall, three years of soy isoflavones treatment showed modest benefits on femur bone density and strength as time since menopause and bone metabolism increased.

Technical Abstract: Soy isoflavones exert inconsistent bone density preserving effects, but the bone strength preserving effects in humans are unknown. Our double-blind randomized controlled trial examined 2 soy isoflavone doses (80 or 120 mg/d) vs placebo tablets on volumetric bone mineral density (vBMD) and strength (by means of peripheral quantitative computed tomography) in healthy postmenopausal women (46e63 yr). We measured 3-yr changes in cortical BMD (CtBMD), cortical thickness (CtThk), periosteal circumference (PC), endosteal circumference (EC), and strength-strain index (SSI) at 1/3 midshaft femur (N=171), and trabecular BMD (TbBMD), PC, and SSI at 4% distal tibia (N=162). We found no treatment effect on femur CtThk, PC, or EC, or tibia TbBMD or PC. The strongest predictors (negative) of tibia TbBMD and SSI and femur CtBMD were timepoint and bone resorption; whole-body fat mass was protective of SSI. As time since last menstrual period (TLMP) increased (p=0.012), 120-mg/d dose was protective of CtBMD. The strongest predictors of femur SSI were timepoint, bone resorption, and TLMP (protective). Isoflavone tablets were negative predictors of SSI, but 80-mg/d dose became protective as bone turnover increased (p<0.011). Soy isoflavone treatment for 3 yr was modestly beneficial for midshaft femur vBMD as TLMP increased and for midshaft femur SSI as bone turnover increased.