Isoflavones and bone health

Phytoestrogens are a family of plant-derived components that present a steroid structure and can act in the estrogen receptor. They contain both estrogenic and antiestrogenic properties, depending on the tissue in which they act. The potential mechanisms by which phytoestrogens can affect cell activities have been divided into genomic and non-genomic effects. The former act through estrogen receptors, and the latter are mediated by cellular proteins. The active mechanism of soy isoflavones in bone may be beneficial, as they act by stimulating the activity of the osteoblasts. On the other hand, through the RANK-L/OPG system they bring about a decrease in osteoclast survival and activity. This article reviews in vitro studies, in animals and humans, that involve isoflavones and bone health to ascertain how these substances affect those postmenopausal women who use them in treatment or prevention of the climacteric syndrome. In general, the global assessment of human studies shows variability in the design, in the variety of isoflavone sources, in the time of the analysis and in the dose. In addition, the variability in the bioavailability and metabolism of isoflavones between the subjects must be considered. All this makes it difficult to obtain consistent conclusions. To sum up, some positive results justify the need for further research. From a clinical point of view, isoflavones are used in women with climacteric symptoms who cannot or do not wish to undergo hormone therapy. They would not be indicated for treating osteoporosis, but those women who use them at the right doses and time can expect a benefit in maintaining bone mass.