This randomized, double-blind, placebo-controlled study conducted in 80 women aged 45 and older and with amenorrhea of > 12 months with vasomotor symptoms (hot flashes and/or night sweats). Women were randomized to receive either 250 mg of standardized soy extract equal to 100 mg/day of isoflavones or placebo for 10 months. There were 40 women in each group. The follow-up period was a duration of 10 months. A total of 32 women in the isoflavone group and 34 women in the placebo group completed the study. No participants were on hormone therapy (HT) or any phytoestrogen within the preceding 6 months.
The purpose of the study was to evaluate the effects of soy isoflavones on breast tissue in postmenopausal women. Breast density was evaluated with mammography and breast parenchyma was evaluated with ultrasound. Each were done at baseline and 10 month follow-up.
At baseline, there were no significant differences between the isoflavone group and the placebo group. After 10 months, the groups did not differ in mammographic density or breast parenchyma by ultrasound. The use of soy isoflavones at 100 mg/day for 10 months did not affect breast density in postmenopausal women.
Commentary: Breast density as characterized on mammography is an independent risk factor for breast cancer. In addition, breast density limits the accuracy of mammography. Results of other randomized, placebo-controlled studies analyzing soy and breast density also did not find breast modifications with soy. An additional insight offered by the results of this study, is that the breast ultrasound also did not detect any increase in fibrosis or fibroglandular tissue with the use of soy isoflavones.
Breast density is influenced by many factors including age, parity, menopause status, body composition, exogenous and endogenous hormones, and genetic factors. The results of the current study lend yet one more comforting piece of data on the safety of soy foods and soy isoflavone extracts on breast health.
Delmanto A, Nahas-Neto J, Traiman P, et al. Effects of soy isoflavones on mammographic density and breast parenchyma in postmenopausal women: a randomized, double-blind, placebo-controlled clinical trial.