Bone FractureFlavonoids (Soy)Menopause

Soy isoflavones to manage postmenopausal osteoporosis

 Researchers from Michigan and Turkey have compiled a comprehensive review of the topic.

Let’s focus on what soy isoflavones are, their value in preventing fractures, and safety.

What are isoflavones?

  • They’re a class of plant estrogens (phytoestrogens) found predominantly in legumes.
  • Soy foods are the most significant source of dietary isoflavones, followed by lentils, kidney beans, lima beans, broad beans, and chickpeas.
  • Nonfermented soy foods, such as roasted soybeans and soy powder, have 2 to 3 times more isoflavones than fermented foods such as miso and tempeh.
  • Soy isoflavones are structurally and functionally related to 17β-estradiol (aka the female sex hormone).
  • 3 major isoflavones found in soybeans are genistein, daidzein, and glycitein.

Only 1 study of isoflavones has focused on fracture prevention.

First, the details.

  • The Shangai Women’s Health Study included 24,403 postmenopausal women who had never used menopausal hormone therapy (MHT) and had no history of fractures or cancer.
  • Dietary intake of soy and its isoflavones was assessed using a questionnaire twice each year for an average of 4.5 years.

And, the results.

  • 1,770 fractures were identified.
  • Higher soy protein and isoflavone intake was associated with a lower risk of fracture.
  • This was particularly true among women with early menopause.


  • Consuming soy foods has many benefits and no adverse effects.
  • However, consuming soy isoflavone supplements is not the same as eating soy foods.
  • Long-term studies are needed to determine the safety of soy isoflavone supplements in humans.

The bottom line?
The authors concluded, “Soy isoflavone supplements are regarded as natural phytoestrogenic products that can be used as an alternative to MHT.” However, the effects of long-term treatment with soy isoflavone supplements on bone fracture and the safety of this supplement need to be established.

Yes, the Shangai Women’s Health Study reported fewer fractures with higher dietary intake of soy and its isoflavones. However, the study had limitations that make it far from the final word on the subject.

Based on the available information, “it is impossible,” say the authors, “to make treatment recommendations at this time.”

10/7/08 18:37 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.