Effects of soy isoflavones on osteoporosis remain unclear. This review aimed to clarify the effect of soy isoflavones on bone mineral density (BMD) and turnover markers in menopausal women. PubMed and the Cochrane Library were searched in July 2011 for relevant meta-analyses of randomized controlled trials evaluating effects of soy isoflavones on BMD and bone turnover markers. Three meta-analyses evaluated the effects of soy isoflavones on lumbar spine, total hip, femoral neck, and trochanter BMD. Soy isoflavones significantly improved lumbar spine BMD in a moderate manner, but did not affect total hip, femoral neck, and trochanter BMD in menopausal women. Ingestion of soy isoflavones for six months appeared to be enough to exert a beneficial effect on lumbar spine BMD. Two meta-analyses evaluated the effects of soy isoflavones on a bone resorption marker (urine deoxypyridinoline) and two formation markers (serum alkaline phosphatase and osteocalcin). Soy isoflavones significantly decreased urine deoxypyridinoline in a moderate manner, but did not affect serum alkaline phosphatase and osteocalcin in menopausal women. Soy isoflavones may prevent postmenopausal osteoporosis and improve bone strength thus decreasing risk of fracture in menopausal women by increasing lumbar spine BMD and decreasing bone resorption marker urine deoxypyridinoline. Further studies are needed to address factors affecting the magnitude of the beneficial effects of soy isoflavones and to assess the possible interactions between soy isoflavones and anti-osteoporosis drugs, and to verify effects on BMD of other skeletal sites and other bone turnover markers.
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