Rev Osteoporos Metab Miner. 2011; 3 (4): 137-8
On this point the evidence is more limited and to date, still confusing. On the one hand is the unfinished business of the symptoms, where there are few clinical studies of quality, and those that there are present difficulties derived from their inclusion of groups with low numbers of participants or of other methodological drawbacks. On the other, there is the question of their eventual efficacy in limiting chronic diseases which more or less clearly have their roots in hypogonadism, such as cardiovascular disease or osteoporosis. The questions in relation to the former have recently been reviewed1, and with respect to the latter, particularly welcome is the article by García-Martín et al. in this issue2.
A literature review regarding the actions of the isoflavones in bone, however, shows that were are dealing with an area in which there are significant discrepancies. For example, a recent clinical trial did not find a protective effect on the bone in women who took tablets containing 200 mg of isoflavones for two years5, and a meta-analysis which examined the action on bone mineral density came to similar conclusions6. However, another meta-analysis found there to be protection, albeit reduced7. Also, with regard to biochemical markers for bone metabolism, a recent meta-analysis found a slight protective action in relation to resorption8. Finally, there is very little information on the effect on ultrasound parameters, and again, in this, the value of the García-Martín study should be highlighted.
How to cast some light on this apparently tricky matter? Evidently, more clinical research is required, but this does not seem to be a simple task due to a series of conditions particular to these types of preparations.
On the one hand, is the great variety of molecules and the differences between their effects, including the metabolic capacities of the individual, which is not the same between, for example, the isoflavones genistein and biochanin A. And in terms of individual metabolisation, it is also important to note that equol, a metabolite of daidzein, is generated by the action of intestinal flora, but only in certain individuals. There are no exact figures, but it is calculated that between 35% and 50% of individuals are capable of producing it. This adds an important factor to the variability of the results of therapeutic actions, given that equol is considered to be one of the most powerful isoflavones. In this area, it would have been useful if the García-Martín2 study had included details of the mixture of isoflavones used.
But on the other hand, there is the response threshold. A meta-analysis which examined the action on vasomotor symptoms found a clear dose-dependent action in a period which reached up to 160 mg/day of isoflavones, with a threshold of acceptability of approximately 80 mg/day9. There are also differences between purified isoflavones and soya protein, at least in the matter of cardiovascular protection, as has been demonstrated in the analysis of the American Heart Association10.
In conclusion, therefore, this is a promising field, but one in which order needs to be imposed. What needs to be clarified is what isoflavones should be used, purified or not, at what dose and, probably, what type of user will obtain, or not, some protective effect. Studies such as that of García Martín are particularly welcome, given their good design which contributes to the accumulation of more evidence.
1. Cano A, García-Pérez MA, Tarín JJ. Isoflavones and cardiovascular disease. Maturitas 2010;67:219-26.
2. García-Martín A, Avilés-Pérez MA, Quesada Charneco M, Jiménez Moleón JJ, Fonollá Joya J, Muñoz-Torres M. Cambios en marcadores del metabolismo óseo y parámetros ultrasónicos en mujeres postmenopáusicas inducidos por isoflavonas de soja. Rev Osteoporos Metab Miner 2011;4:141-46.
3. Marini H, Minutoli L, Polito F, Bitto A, Altavilla D, Atteritano M, et al. OPG and sRANKL serum concentrations in osteopenic, postmenopausal women after 2-year genistein administration. J Bone Miner Res 2008;23:715-20.
4. Reyes-García R, Rozas-Moreno P, Muñoz-Torres M. Cardiovascular disease and bone metabolism. Endocrinol Nutr 2011;58:353-9.
5. Lewis S, Strickman-Stein N, Ganjel-Azar P, Xu P, Doerge DR, Krischer J. Soy isoflavones in the prevention of menopausal bone loss and menopausal symptoms: a randomized, double blind trial. Arch Intern Med 2011;171:1363-9.
6. Liu J, Ho SC, Su YX, Chen WQ, Zhang CX, Chen YM. Effect of long-term intervention of soy isoflavones on bone mineral density in women: a meta-analysis of randomized controlled trials. Bone 2009;44:948-53.
7. Ma DF, Qin LQ, Wang PY, Katoh R. Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta-analysis of randomized controlled trials. Clin Nutr 2008;27:57-64.
8. Taku K, Melby MK, Kurzer MS, Mizuno S, Watanabe S, Ishimi Y. Effects of soy isoflavone supplements on bone turnover markers in menopausal women: systematic review and meta-analysis of randomized controlled trials. Bone 2010;47:413-23.
9. Howes LG, Howes JB, Knight DC. Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas 2006;55:203-11.
10. Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M. American Heart Association Nutrition Committee. Circulation 2006;113:1034-44.