Flavonoids (Soy)Phytoestrogens

Conflicting results on the value of soy isoflavones on bone

Two studies published this year came to different conclusions on the value of soy isoflavones to prevent bone resorption (breakdown) in postmenopausal women.

First, the positive results.

  • 90 women, 45 to 60 years old, took placebo, or 84 or 126 mg of isoflavones each day for 6 months.
  • The higher daily dose of isoflavones prevented postmenopausal bone loss in the spine and neck of the thigh.

These researchers from Sun Yat-sen University in Guangzhou, China believe that past study results were disappointing because the dosages of isoflavones used were too low.

Maybe, but what about these negative results

  • 13 women (at least 6 years past menopause) were given 43 grams of soy protein per day that contained 0, 97.5, or 135.5 mg of total isoflavones in random 50-day periods.
  • There was no measurable effect on bone (even at the higher dose).


Both studied small groups of women and used different methods of measuring the effect of isoflavones on bone. Most importantly, neither study measured the rate of fractures — the reason women would want to take soy products in the first place.

Here’s what we know.

  • Soy isoflavones have weak estrogen-like activity.
  • This might be the mechanism of their benefits.
  • In the largest epidemiological study of soy food consumption and fracture incidence, more than 24,000 postmenopausal Chinese women with no history of fracture or cancer found that soy consumption reduced the risk of fracture.
  • The results were most apparent in women who were in early post-menopause.

Perhaps the secret is to identify subgroups of women that are the best candidates for treatment.

The Osteoporosis Prevention Using Soy (OPUS) study is a multi-site, long-term research study on the use of soy isoflavone supplementation to prevent bone loss in postmenopausal women. The results are close to being published. We should know more in the next year.

Unfortunately, it’s not designed to compare fracture rates.

12/9/06 11:42 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 www.Vicus.com, a complementary and alternative medicine website.