Soybean Isoflavones in Bone Health

National Institute of Health and Nutrition, Tokyo, Japan.
Forum of nutrition 02/2009; 61:104-16. DOI: 10.1159/000212743
Source: PubMed


Soybean isoflavones are structurally similar to estrogen, bind to estrogen receptors, and exhibit weak estrogenic activity. It has been reported that isoflavones play an important role in the prevention of hormone-dependent diseases, including osteoporosis, cardiovascular diseases, cancer, and postmenopausal syndrome. There are many researches indicating isoflavones prevent bone loss caused by estrogen deficiency in animal models. Furthermore, it has been demonstrated that a combination of isoflavone treatment and exercise cooperatively prevented bone loss in the estrogen-deficient status. Epidemiological studies demonstrated the relationship between the lower incidence of osteoporosis in Asian women and a diet rich in soy foods. Although a number of observational studies confirm the findings from the animal studies, the results from intervention studies are still controversial. One of the potential reasons for these inconsistencies could be individual differences in the isoflavone metabolism. Recently, it has been suggested that the clinical effectiveness of isoflavones might partly depend on the ability to produce equol, a gut bacterial metabolite of daidzein showing stronger estrogenic activity than the predominant isoflavones. Several candidate bacteria responsible for equol production have been suggested, for example Lactococcus 20-92 strain. From these findings, food factors enhancing equol production have received great deal of attention recently. On the other hand, safety assessment of isoflavones has been conducted by the Japanese Food Safety Commission. Further studies are required to address the numerous questions on the potential benefits, mechanisms of action, and safety of isoflavones.

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    • "Epidemiological studies and clinical trials have shown that phytoestrogens have a protective effect against postmenopausal symptoms; cardiovascular disease; bone health problems; breast, prostate, and colon cancers; and postmenopausal syndrome due to their structural similarity to estrogen (Bhathena and Velasquez 2002; Duncan et al. 2003; Ishimi 2009; Messina 1999; Setchell and Cassidy 1999). This review article discusses the role of metabolites of phytoestrogens that have been hydrolyzed by probiotics or intestinal microflora and how such metabolism improves the actions of these phytoestrogens in mimicking mammalian estrogens, thereby preventing postmenopausal bone loss. "
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    ABSTRACT: Phytoestrogens are a class of bioactive compounds derived from plants and exert various estrogenic and antiestrogenic effects. Estrogen deficiency osteoporosis has become a serious problem in elderly women. The use of ovariectomized (OVX) rat or mice models to simulate the postmenopausal condition is well established. This review aimed to clarify the sources, biochemistry, absorption, metabolism, and mode of action of phytoestrogens on bone health in intervention studies. In vitro, phytoestrogens promote protein synthesis, osteoprotegerin/receptor activation of nuclear factor-kappa B ligand ratio, and mineralization by osteoblast-like cells (MC3T3-E1). In the OVX murine model, administration of phytoestrogens can inhibit differentiation and activation of osteoclasts, expression of tartrate-resistant acid phosphatase, and secretion of pyridinoline compound. Phytoestrogens also enhance bone formation and increase bone mineral density and levels of alkaline phosphatase, osteocalcin, osteopontin, and α1(I) collagen. Results of mechanistic studies have indicated that phytoestrogens suppress the rate of bone resorption and enhance the rate of bone formation.
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