Osteoporosis, a decrease in the density of the bones leading to susceptibility to fracture, is very common among post-menopausal Caucasian women. Since before menopause, estrogen levels are higher, estrogen replacement therapy is sometimes prescribed for post-menopausal women at risk for osteoporosis who want to minimize bone mineral loss.
However, the effects of estrogen on the body are complex, so estrogen replacement comes at a price, including increased risk for heart disease and breast cancer. Soy isoflavones can act as estrogen mimics and supplementation with them has become a popular alternative to hormone replacement therapy. However, studies examining the effectiveness of soy isoflavones in increasing bone mineral density in post-menopausal women have yielded contradictory results.
In an effort to determine if the combined results of the previously published studies on the increase in bone mineral density or content with intake of soy isoflavones are significant, the researchers recently selected 10 published studies out of 675 potential ones. The majority were eliminated from inclusion because they were not randomized or controlled.
The ten studies (608 subjects) which were included in the meta-analysis examined soy protein intake (containing a known amount of isoflavones) over a period of six months or more in peri or post-menopausal women and included a control group. Results were reported using changes in spine bone mineral density (SBMD) and spine bone mineral content (SBMC) from baseline.
When the 10 studies were analyzed together, intake of isoflavones significantly increased SBMD by 20.6 mg/cm2 (95% confidence interval, CI = 4.5–36.6 mg/cm2, p = 0.01).
Subgroup analysis showed that more than 90 mg per day of isoflavone supplementation was necessary to see significant change, and that post-menopausal women benefited more significantly than peri-menopausal women. SBMC also improved with supplementation but to a less significant degree.
Ma D-F, et al. Soy isoflavone intake increases bone mineral density in the spine of menopausal women: Meta-analysis of randomized controlled trials. Clin Nutr (2007), doi:10.1016/j.clnu.2007.10.012.