Soy Pills Fail to Prevent Bone Loss

Soy Pills Fail to Prevent Bone Loss
By John Gever, Senior Editor, MedPage Today
Published: September 15, 2009
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine



Soy protein extracts showed no evidence of preventing bone loss in postmenopausal women in two placebo-controlled trials, researchers reported here at the American Society for Bone and Mineral Research meeting.

In one trial with 224 participants, very similar declines in lumbar spine and hip bone mineral density (BMD) were seen after three years in women taking the soy pills and those taking placebo.

The other study found that levels of a biomarker of bone resorption were virtually identical after two years of high-dose soy extracts versus placebo.

"I think we can close the door on this issue," declared the first study's leader, D. Lee Alekel, PhD, of Iowa State University in Ames.

Previous studies had yielded conflicting results as to whether the isoflavones in soybeans prevented bone loss. A retrospective Chinese study reported in 2005 had found a strong preventive effect in women who had consumed large quantities of soy foods. (See More Soy in the Diet Means Fewer Fractures for Women)
Action Points
--------------------------------------------------------------------------- â– Explain to interested patients that soybeans contain estrogen-like compounds that interact with estrogen receptors, although the effects are not the same as with natural human estrogens.
â– Explain that these studies were randomized, placebo-controlled trials, a very strong form of evidence.
â– Explain that these studies used soy extracts and may not be generalizable to whole soybean-based foods, which could affect bone health through different mechanisms.
â– Note that these studies were published as abstracts and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.


Alekel said an earlier study in her own lab had found a modest benefit in perimenopausal women.

But other studies had either failed to find any benefit for the soy extracts or were marred by small numbers of participants or other limitations.

Alekel's study randomized 224 healthy postmenopausal women, mean age 54, to take placebo or 80 or 120 mg of soy isoflavones in pill form for three years.

They also received daily supplements of 500 mg of calcium and 600 IU of vitamin D.

The researchers ran multivariate analyses of BMD changes that included age, treatments, whole body fat mass, and the CTX biomarker of bone resorption, at three standard sites: lumbar spine, proximal femur, and femoral neck.

Alekel said the analyses showed that the 120-mg dose of soy was modestly protective at the femoral neck, relative to placebo (parameter estimate -1.223, P=0.024) in women who took at least 80% of their assigned medications on schedule.

But no significant benefit was found for the soy pills in any other measure. Whole body fat mass, age, and CTX levels were much more predictive of BMD loss, she said.

The other study, led by Silvina Levis, MD, of the University of Miami, found no effect on a biomarker of bone resorption after two years of treatment with placebo or 200 mg/day of soy isoflavone pills.

Participants were 248 postmenopausal women, average 53 years old, about two-thirds of whom were Hispanic whites.

Levis and colleagues reported that levels of urinary N-telopeptide of type I bone collagen (NTx) -- like CTX a measure of bone resorption -- did not differ between treatment groups after one and two years of treatment.

The study -- called SPARE (Soy Phytoestrogen As Replacement Estrogen) -- also included measurements of lumbar spine and hip BMD, but those data were not reported here.

Peter Burckhardt, MD, who studied nutrition and endocrinology at the University Hospital of Lausanne in Switzerland until his recent retirement, said the studies' findings did not surprise him.

"The overall evidence in the literature is negative," he said.

Burckhardt said one of the earlier studies that purported to find a benefit was misleading.

"[It] was published in a high-ranking journal with an attractive title that it worked. But when you go into the data you discover that it worked only in a subgroup and only with a special [bone measurement]," he said.

Referring to the Iowa State study of BMD, Burckhardt said, "It looks solid."

He added that women continued to try over-the-counter soy supplements "because it's easy. It's lovely to trust in something that looks easy."

Alekel emphasized that the negative results apply only to the soy extracts used in the studies. She said soy foods, consumed over a lifetime, could well help women limit bone loss and fractures, just because such foods may be less fattening and have other health benefits.

Nevertheless, she said, it now appears certain that soy phytoestrogens do not have the same bone-protective effects at estrogen receptors seen with mammalian estrogens.

Both studies were funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

Alekel, Levis, and Burckhardt said they had no relevant conflicts of interest.


Primary source: American Society for Bone and Mineral Research
Source reference:
Alekel D, et al "Soy Isoflavones for Reducing Bone Loss (SIRBL) study: randomized three year intervention in postmenopausal women" ASBMR 2009; Abstract SA0412.

Additional source: American Society for Bone and Mineral Research
Source reference:
Levis S, et al "Soy isoflavones and bone resorption: results of the Soy Phytoestrogens as Replacement Estrogen (SPARE) study" ASBMR 2009; Abstract MO0374.