Effects of the Phytoestrogen Genistein on Bone Health in Postmenopausal Women

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The summary below is from the full report titled "Effects of the Phytoestrogen Genistein on Bone Metabolism in Osteopenic Postmenopausal Women. A Randomized Trial." It is in the 19 June 2007 issue of Annals of Internal Medicine (volume 146, pages 839-847). The authors are H. Marini, L. Minutoli, F. Polito, A. Bitto, D. Altavilla, M. Atteritano, A. Gaudio, S. Mazzaferro, A. Frisina, N. Frisina, C. Lubrano, M. Bonaiuto, R. D'Anna, M.L. Cannata, F. Corrado, E.B. Adamo, S. Wilson, and F. Squadrito.

What is the problem and what is known about it so far?

As people age, their bones become less dense and bone fractures occur more easily. Estrogen helps to maintain bone health in younger women, but after about 30 years of age, estrogen levels begin to decrease and then fall sharply after menopause. Estrogen replacement therapy is effective at maintaining bone, but because of its side effects, it is no longer recommended for this purpose.

Many women who are looking for "natural" ways to promote bone health use phytoestrogens. Phytoestrogens are naturally occurring estrogen analogues, which are found in soy products. Genistein is a phytoestrogen that is a common ingredient of products marketed to promote bone health. Typically, however, the level of genistein in these products is too low to be effective. Also, the effectiveness of phytoestrogens such as genistein has not been carefully studied.

Why did the researchers do this particular study?

To find out whether genistein improves bone health in postmenopausal women with osteopenia.

Who was studied?

389 postmenopausal women with osteopenia who were otherwise healthy.

How was the study done?

The researchers assigned patients to take 2 pills that contained a total of 54 mg of genistein or a placebo pill daily for 24 months. Both pills contained vitamin D₃ and calcium, which are necessary for healthy bones. The placebo pills contained no other active ingredients. The researchers measured bone density and performed several blood tests to see whether bone breakdown and formation occurred after 24 months. Because estrogens can make the lining of the uterus thicker and can lead to cancer, the researchers used ultrasound tests to measure the thickness of the lining of the uterus to see whether genistein also caused this side effect.

What did the researchers find?

After 24 months, women who took genistein had a greater increase in bone mineral density than the women who took the placebo. In addition, bone markers were more favorable in women taking genistein than in women taking placebo. Gastrointestinal side effects were more common among women taking genistein than in women taking placebo. The thickness of the lining of the uterus did not change in either group, suggesting that genistein may be safe to use in terms of uterine health.

What were the limitations of the study?

The study had too few participants and was too short to determine whether genistein reduces fractures and whether side effects might become more of a problem when genistein is used for longer than 24 months.

What are the implications of the study?

The phytoestrogen genistein, when taken with vitamin D₃ and calcium, has favorable effects on bone health compared with vitamin D₃ and calcium alone.