Soy Isoflavone Tablets Do Not Appear to Prevent Menopausal Bone Loss
By Nancy A. Melville
Medscape Medical News
September 24, 2009 (Denver, Colorado) — Studies presented here at the American Society for Bone and Mineral Research 31st Annual Meeting cast doubt on the theory that a high isoflavone intake could help slow bone loss related to menopause.
With hormone replacement therapy falling out of favor after findings from the Women's Health Initiative linked estrogen and progestin therapies to breast cancer and cardiovascular complications, some women turned to soy in the belief that its high isoflavone content could help prevent or slow menopause-related bone loss.
Findings from 2 studies presented here do not support that theory.
The first involved 248 menopausal women with a mean age of 52.5 years; 66% were Hispanic and none had osteoporosis at baseline. The researchers randomized the women in equal proportions to receive either soy isoflavone 200?mg daily or placebo over the course of 2 years.
Throughout the study, the researchers observed that N-telopeptide of type?I bone collagen levels remained constant for both the soy and placebo groups. The researchers concluded that "purified soy isoflavones do not influence bone resorption in women in the first 5 years of menopause."
The researchers say they plan future studies to assess the effectiveness of soy isoflavones in preventing postmenopausal bone loss and menopausal symptoms.
The second study was a randomized double-blind trial comparing the effects of 80?mg or 120?mg daily soy isoflavone tablets or matching placebo in 3 groups of postmenopausal women between the ages of 45 and 65 years. The women in each group also received daily calcium 500?mg and daily vitamin D3 600?IU.
Among the 209 subjects who completed the 3-year study, the researchers found no significant differences in lumbar spine, hip, or whole-body bone mineral density (BMD) among the 3 groups; however, the 120?mg dose did show a significant protective effect on femoral neck BMD (P?= .024). Factors other than soy, including age, whole-body fat mass, and cross-linked C-terminal telopeptides of type?I collagen, were found to be common predictors for bone outcome among the subjects.
Soy isoflavone treatment was not associated with adverse events. Over the 3-year study period, endometrial thickness declined, serum 25(OH) vitamin?D levels increased, and biochemical markers of bone turnover did not change.
Lead author D. Lee Alekel, PhD, professor of nutrition at Iowa State University's Nutrition and Wellness Research Center in Ames, said the findings countered the researchers' original hypothesis about potential benefits from soy isoflavone, and, in the context of the other predictors of bone outcome, the modest protection seen in femoral neck BMD did not qualify as strong enough evidence to suggest otherwise.
"We hypothesized that isoflavone tablets would spare BMD, with biologic [age, body weight, serum 25(OH) vitamin?D] and lifestyle [physical activity, dietary intake] factors modulating BMD loss," she said.
"[After] adjusting for these factors, the 120?mg [dose] was protective (P?= .024) for femoral neck BMD. However, in comparison with whole-body fat mass or age, the higher-dose treatment exerted minimal effect on the femoral neck."
Dr. Alekel noted that previous studies have also negated benefits from soy isoflavone tablets on bone protection.
"Aside from the results of our study, other studies examining the effect of soy isoflavone tablets on bone for postmenopausal women have demonstrated little effect on bone mineral density," she said.
"The bone sites of interest for osteoporotic risk should be the lumbar spine and proximal femur (hip) rather than whole-body bone. At best, some studies have indicated a small bone-sparing effect, while most well-conducted studies have shown little biological response," Dr. Alekel noted.
Clifford J. Rosen, MD, senior scientist at Maine Medical Center's Research Institute in Portland, agreed that the studies add to a growing body of research that cast doubt on any therapeutic benefits of soy isoflavones in preventing menopausal bone loss.
"Randomized trials provide strong evidence that there is little effect of soy or isoflavones on bone turnover," he said, adding that the effect of soy on the femoral neck seen in Dr. Alekel's study likely doesn't change that conclusion. "The very modest effects on femoral bone mass are probably not clinically significant."
Both studies received support from the National Institute of Arthritis Musculoskeletal & Skin Diseases, NIH. Drs. Alekel and Rosen have disclosed no relevant financial relationships.
American Society for Bone and Mineral Research (ASBMR) 31st Annual Meeting: Abstracts SA0412 and MO0374. Presented September 11-15, 2009.
