Joanna Cosgrove02.11.10
Bone loss is a serious issue for postmenopausal women. Although there are osteo-protective pharmaceuticals formulated to address the problem, women seeking natural alternatives have traditionally sought the phytoestrogens found in soy isoflavone supplementation because previous research suggested that a diet including isoflavone-rich soy foods could help protect against bone loss. But while there have been many clinical studies and meta-analyses seeking to sort out soy isoflavones’ bone benefits, the findings have been divergently mixed.
Two separate research teams—each funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (part of the NIH)—set out to get to the bottom of the matter. Their findings were presented at a recent American Society for Bone and Mineral Research meeting and the facts they uncovered may have effectively “closed the door” on soy’s purported bone protection benefits.
In 2004, researchers at The Osteoporosis Center at the University Of Miami School Of Medicine began a five-year NIH study called “phytoestrogens as replacement estrogen” (SPARE) to determine if soy supplements could preserve bone health and ease menopausal symptoms in the first years of menopause.
Led by Silvina Levis, MD, of the University of Miami, the research team studied 248 postmenopausal women with an average age of 53 years, who were administered either a placebo or 200 mg per day of soy isoflavones in pill form. They ultimately found no measure of bone resorption following two years of treatment in either group.
The second study, Soy Isoflavones for Reducing Bone Loss (SIRBL), was a three-year randomized controlled trial in postmenopausal women that examined the efficacy of soy protein isoflavones on bone mineral density (BMD) in nonosteoporotic postmenopausal women. For this study, the research team set out with the hypothesis that isoflavone tablets would spare BMD, with biological and lifestyle factors modulating BMD loss.
For this study, 224 healthy postmenopausal women between the ages of 45 and 65 years old were given either a placebo or one of two soy isoflavone doses—80 or 120 mg per day. The women also received 500 mg calcium and 600 IU vitamin D3 per day.
“We embarked upon this NIH-funded clinical trial because preliminary data from our previous study with perimenopausal women, as well as the literature, suggested that the isoflavones from soy protein were the bioactive components with respect to the skeleton,” explained lead study author, D. Lee Alekel, PhD, professor of nutrition, and interim associate director of Iowa State University’s Nutrition & Wellness Research Center in Ames, IA. “Women are taking supplements with isoflavones extracted from soy protein with the expectation that these compounds will benefit bone. When we started our SIRBL study, there were no long-term (two to three year) studies, nor were there well designed human studies published in this area.”
At the conclusion of the study, the researchers found that soy isoflavones did not exhibit “a bone-sparing effect…except for a modest effect at the femoral neck.” In fact, whole body fat mass, age and CTX levels had a more profound effect on BMD loss.
Dr. Alekel said she found the results to be somewhat unsurprising. “Although we had hypothesized that soy isoflavones would attenuate bone loss in these women, the results were not entirely surprising because it is very difficult to demonstrate long-term efficacy with a non-pharmaceutical intervention,” she said. “Despite excellent compliance, we could not demonstrate a robust treatment effect in these women (we noted a modest effect on the femoral neck region).”
Dr. Alekel said she had no further research plans to study soy and its relation to bones, however, she and her colleagues are currently completing a study comparing the effects of a soy beverage versus cow’s milk on prehypertension and stage 1 hypertension in young adults.
