Investigators from the School of Heilongjiang Bayi Agricultural University and Harbin Medical University in China recently evaluated the effects of isoflavones on hot flashes and bone mineral density of the radius and tibia. For this 6-month study, 80 women were randomly divided into two groups; one received a placebo and the other 90 mg/day isoflavones. The isoflavone supplement was comprised of 52.2% genistein and 47.8% daidzein. The dropout rate was less than 20%, as 37 women completed the trial in the isoflavone group and 33 in the placebo group.
Conducting isoflavone trials in Asia can be problematic because of background exposure. That is, individuals in Asia are often consuming significant amounts of soyfoods and hence, ingesting considerable amounts of isoflavones. However, for this study, women were asked to greatly limit or abstain from eating soyfoods. At study conclusion, blood isoflavone levels were >10-fold higher in the isoflavone group compared to the placebo group.
The results showed several significant effects of isoflavones. Most importantly, hot flash frequency decreased by 63.8% in the isoflavone group but by only 16.3% in the placebo group. Also, in the isoflavone group, tibia bone density increased whereas tumor necrosis factor-alpha decreased. One limitation of this study is that hot flashes were only measured at the beginning and at the conclusion of the study. On the other hand, the length of the study provides assurance that the effects were not transient.
Chi X-X, Zhang T. The effects of soy isoflavone on bone density in north region of climacteric Chinese women. J Clin Biochem Nutr 2013;53:102–107.