ARS | Publication request: Soy Isoflavones for Reducing Bone Loss (SIRBL) Study: Randomized Three Year Intervention in Postmenopausal Women

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2009
Publication Date: November 11, 2009
Repository URL: http://www.ajcn.org/content/91/1/218.long
Citation: Alekel, D.L., Van Loan, M.D., Koehler, K.J., Hanson, L.N., Stewart, J.W., Hanson, K.B., Genschel, U., Gertz, E.R., Kurzer, M.S., Peterson, C.T., Beer, B. 2009. Soy Isoflavones for Reducing Bone Loss (SIRBL) Study: Randomized Three Year Intervention in Postmenopausal Women. American Society for Bone and Mineral Research. 91(1):218-30.

Technical Abstract: Research has indicated that soy protein with isoflavones may attenuate bone loss in postmenopausal women. We hypothesized that soy isoflavones would decrease bone loss in healthy postmenopausal women (45.8-65.0 years) by maintaining bone mineral density (BMD), and this bone-sparing effect would be greater in women receiving the higher dose. We anticipated the effect would be modulated by isoflavone metabolism (reflected by urinary equol) and biologic (age, body weight, vitamin D status) and lifestyle (physical activity, dietary intake reflected by urinary mineral excretion) factors. We examined the effect of soy isoflavone (80 mg/d vs. 120 mg/d vs. placebo control) tablets on lumbar spine (LS), proximal femur (hip), femoral neck (FN), and whole body (WB) BMD in postmenopausal women, randomized (double-blind) to treatment for 36 months. Women in each group also received calcium (500 mg/d) and vitamin D3 (600 IU/d). The intent-to-treat (ITT; N=224) and compliant (N=209) models (>80% cumulative compliance), respectively, indicated no treatment effect for LS (p=0.46, p=0.21), hip (p=0.86, p=0.46), FN (p=0.17, p=0.14), or WB (p=0.86, p=0.78) BMD. BMD declined from baseline to 36 months (based upon ITT and compliant models, respectively): LS (-2.08%, -1.99%), hip (-1.43%, -1.38%), neck (-2.56%, -2.51%), WB (-1.66%, -1.62%). Regression analysis for compliant women indicated that age, whole body fat mass, and cross-linked C-terminal telopeptides of type-I-collagen were common predictors for each bone outcome; the 120 mg dose exerted a significant protective effect (P=0.024) on percentage decline only for FN BMD. There was no effect of soy isoflavone treatment on adverse events, endometrial thickness (declined from baseline through 36 months), serum 25(OH) vitamin D (increased from baseline through 36 months), or biochemical markers of bone at any time point. This study was longer (36 months) than previous studies and used soy isoflavones extracted from soy protein rather than intact soy protein or isolate. Our results did not indicate a bone-sparing effect of soy isoflavones, except perhaps a modest effect at the FN, once other factors were taken into account.