Aim: 

We investigated in a 2-year randomized, double-blind, placebo-controlled study whether pure administration of phytoestrogen genistein (54 mg/day) might reduce the number and severity of hot flushes in postmenopausal women, with no adverse effect on the endometrium and vagina.

Methods: 

A total of 389 participants met the main study criteria and were randomly assigned to receive genistein (n = 198), daily, or placebo (n = 191). About 40% of participants in both groups did not suffer from hot flushes, and the evaluation was performed in a subgroup of 236 participants (genistein, n = 119; placebo n = 117). Reductions from baseline in the frequency and severity of hot flushes were the principal criteria of efficacy. Endometrial thickness (ET) was evaluated by ultrasonography. The Maturation Value (MV) was also used to determine hormonal action on the vaginal cells.

Results: 

There were no significant differences in vasomotor symptoms between groups at baseline (4.4 0.33 hot flushes per day in the genistein group and 4.2 0.35 hot flushes per day in the control group). After 12 months of genistein therapy there was a considerable reduction (-56.4%) in the mean number of hot flushes, with a significant difference compared to the control group. After 24 months no further decrease in hot flushes number in both groups. No significant difference was found in mean ET and MV score between the two groups, either at baseline or after 24 months.

Conclusions: 

The phytoestrogen genistein has been shown to be effective on vasomotor symptoms without an adverse effect on endometrium and vagina.