Soy isoflavone tablets do not appear to be associated with a reduction in bone loss or menopausal symptoms in women within the first five years of menopause, according to a report in the August 8 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
The beginning stages of menopause are often accompanied by rapid bone loss, hot flashes, vaginal dryness and sleep disturbances among other symptoms, according to background information in the article. "Estrogen therapy with or without progesterone prevents most of these changes. However, as a result of the Women's Health Initiative findings suggesting that the overall risks outweigh the benefits, most menopausal women now decline estrogen therapy, increasingly seeking other alternatives," the authors write. "Soy-derived products have been proposed to provide comparable benefits to estrogens but without the risks."
Silvina Levis, M.D., of the Miami Veterans Affairs Healthcare System and Miller School of Medicine, University of Miami, and colleagues, conducted a randomized controlled trial from July 2004 to March 2009 to determine the effectiveness of soy isoflavone tablets in preventing bone loss and other menopausal symptoms. Study participants received a soy isoflavone dose equivalent to approximately two times the highest intake through food sources in a typical Asian diet to ensure they received an effective dose. Women 45 to 60 years of age, within five years of menopause and with a bone mineral density T score (bone density compared with what is normally expected in a healthy young adult of the same sex) of -2.0 or higher in the lumbar spine or total hip were eligible for the study.
A total of 248 women were eligible for the study; 126 were randomized to the group receiving placebo tablets and 122 were randomized to the soy isoflavone group, who received 200 mg of soy isoflavone tablets daily. During two years of follow-up, no significant differences were found between women in the soy isoflavone group and placebo group regarding changes in bone mineral density of the spine (-2 percent vs. -2.3 percent), the total hip (-1.2 percent vs. -1.4 percent) or the femoral neck (-2.2 percent vs. -2.1 percent), respectively.
Additionally, the number of menopausal symptoms was comparable between the two groups at baseline and the end of the study, except hot flashes. At the end of the study, 48.4 percent of women in the soy isoflavone group and 31.7 percent of women in the placebo group reported hot flashes. The authors also found that a higher number of women in the soy group reported constipation compared with women taking placebo (31.2 percent vs. 20.6 percent) but this was not statistically significant.
"Because of concerns regarding the risk of estrogens, a need exists for alternative interventions that could provide the beneficial effects of estrogens in bone and menopausal symptoms without the adverse effects on breast and cardiovascular health," the authors conclude. However, "we found that our population of women in the first five years of menopause, on average, had low rates of bone loss, and that 200 mg of soy isoflavone tablets taken once daily does not prevent bone loss or reduce bone turnover or menopausal symptoms."
Commentary: Soy Isoflavones for Prevention of Menopausal Bone Loss and Vasomotor Symptoms
"Every woman who lives long enough will go through the menopause transition; approximately 80 percent will experience hot flashes and night sweats, and approximately 20 percent will experience sufficient discomfort to seek treatment," write Katherine M. Newton, Ph.D., of the Group Health Research Institute, Group Health Cooperative, Seattle, and Deborah Grady, M.D., M.P.H., of the University of California, San Francisco and San Francisco VA Medical Center.
"In this issue of the Archives, Levis et al report the results of the National Institutes of Health-funded Soy Phytoestrogens as Replacement Estrogens (SPARE) trial," the authors write. "The SPARE study was designed to overcome the limitations of many prior trials of soy products, including poor design, small sample size and short duration."
The authors do note that, "the main shortcoming of the study was that only 248 of an expected 306 participants were enrolled, and higher-than-expected dropout rates led to a final sample size substantially lower than that predicted." However, even with the smaller sample size, "given the virtually identical results in the two groups, it is difficult to imagine that the results would have differed substantially with additional participants or better retention," the authors write. "Overall it does not appear that soy supplementation will play an important role in osteoporosis prevention."
"To some extent, we are constrained because the mechanism of hot flashes and night sweats remains unknown," the authors conclude. "Perhaps efforts should be directed away from the hope of a one-size-fits-all therapy for menopausal symptoms toward using existing treatments to target the symptoms that disturb patients most."