Effects of phytoestrogens on bone mineral density during the menopause transition: a systematic review of randomized, controlled trials

Introduction: Menopause is associated with increased bone resorption and decreased bone mineral density (BMD). Phytoestrogens are believed to prevent bone loss. This study reviewed relevant randomized, controlled trials to determine the effects of phytoestrogens on BMD in postmenopausal women. Methods: In order to perform this systematic review, PubMed, Science Direct, Scopus, Cochrane Library, ISI Web of Knowledge, and ProQuest databases were searched for articles published during 2005-2016. The main keywords used during the searches were "phytoestrogen" and "bone mineral density" and "menopause". The Cochrane Risk of Bias Assessment Tool was used to evaluate the quality of the selected studies and to assess the risk of bias. Results: A total of 23 eligible studies were included in this systematic review. Most selected studies used a double-blind, placebo-controlled design. In total, 3494 participants were enrolled in the selected trials. Different types of soy isoflavone extracts, including genistein extracts (either alone or in combination with daidzein), dietary products containing different amounts of phytoestrogens, and red clover extracts were used in the designed interventions. The duration of the interventions ranged from 7 weeks to 3 years. In most studies, the primary outcome was the efficacy of the designed intervention which was assessed through measuring whole body or regional BMD or bone mineral content, T-scores, and biomarkers of bone metabolism. Conclusions: Isoflavones probably have beneficial effects on bone health in menopausal women. Nevertheless, there were controversial reports about changes in BMD. Supplementation with a phytoestrogen can probably prevent the reduction in BMD and maintain a healthy bone structure during menopause.