Phytoestrogens and bone health at different reproductive stages

BACKGROUND: Isoflavones are an alternative to hormonal therapy for the relief of menopausal symptoms. Since isoflavones interact with estrogen receptors it has been hypothesized that such substances may have an effect on bone health. OBJECTIVE: To clarify the effect of isoflavones on bone at experimental and clinical level, and to identify areas that require further clarification and research. METHOD: A systematic review of studies involving isoflavones and bone health was performed, and a specific search on isoflavone's mechanism of action and the importance of equol production was made based on Internet search engines, MEDLINE (1966-October 2012) and the Cochrane Controlled Clinical Trials Register. This search was supplemented by a handsearch of reference lists of selected papers. RESULTS: In vitro and animal studies show a positive effect of isoflavones on bone which has not been clearly confirmed by long-term human trials. Equol producers seem to present a more positive response to isoflavone intervention. Isoflavone rich diets could help maintain peak bone mass in premenopausal women. The effect of isoflavones in perimenopausal women is insufficiently studied but it seems to attenuate bone loss in the menopausal transition. In postmenopause, isoflavones may present a modest benefit but its clinical relevance in preventing osteoporotic fractures remains to be determined. CONCLUSIONS: The present review suggests that isoflavone increase bone mineral density and decrease the bone turnover resorption markers. The effect of soy isoflavones on BMD is mediated by equol production, reproductive status, supplement type, isoflavone dose and intervention duration.