Isoflavones: effects on bone health.

Background: There are many effects described, both experimental and clinical, that assess the relationship between isoflavones and bone. It has been hypothesized that isoflavones may have a positive effect on bone health.

Objective: To review the effects of isoflavones on biochemical markers of bone remodeling, bone density and bone quality, and finally on fracture incidence.

Methods: A systematic review was carried out of in vitro, animal, and human studies involving isoflavones and bone health. An electronic search was made, based on Internet search engines, MEDLINE (1966-June 2010) and the Cochrane Controlled Clinical Trials Register. This search was further supplemented by a hand-search of reference lists of selected review papers.

Results: After crossing-cleaning the reference lists, 737 studies dealing with isoflavones and bone were identified. Of these, 36 were considered selectable. From in vitro and animal studies, isoflavones appear to stimulate osteoblastic bone formation and inhibit osteoclastic bone resorption. Reviewed data show evidence of a beneficial effect of isoflavones on bone health in peri- and postmenopausal women when high-isoflavone soy protein is incorporated in the diet. Inconsistencies observed among data from different studies are related to differences in study design, the variety of soy sources of isoflavones, time of analysis, and the variability in the bioavailability and metabolism of isoflavones.

Conclusions: Most of the studies suggested a positive relationship between isoflavones and bone health. Further well-controlled, randomized, double-blind, clinical trials with a larger sample population, longer duration, and examination of various dosages are needed to better elucidate the inter-relationship between isoflavones and bone loss and to clarify whether isoflavones could prevent bone fractures.