Skip Navigation LinksHome > August 2013 - Volume 20 - Issue 8 > Effect of isoflavone soy protein supplementation on endometr...
Menopause:
doi: 10.1097/GME.0b013e3182804353
Original Articles

Effect of isoflavone soy protein supplementation on endometrial thickness, hyperplasia, and endometrial cancer risk in postmenopausal women: a randomized controlled trial

Quaas, Alexander M. MD, PhD1; Kono, Naoko MPH2; Mack, Wendy J. PhD2,3; Hodis, Howard N. MD2,3,4; Felix, Juan C. MD5; Paulson, Richard J. MD1; Shoupe, Donna MD1

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Abstract

Objective

This study aims to determine whether long-term isoflavone soy protein (ISP) supplementation affects endometrial thickness and rates of endometrial hyperplasia and cancer in postmenopausal women.

Methods

In this randomized, double-blind, placebo-controlled trial, 350 postmenopausal women aged 45 to 92 years were randomized to a total daily dose of 154 mg of ISP or a milk protein–matched placebo for a 3-year period. Women with a surgically absent uterus were excluded from the analysis (final study population, N = 224). The main outcome measures were as follows: mean change in endometrial thickness on transvaginal ultrasound from baseline until up to 36 months of follow-up and the incidence of endometrial sampling, endometrial hyperplasia, and endometrial cancer.

Results

A total of 666 visits among 224 participants were evaluated. Treatment groups did not significantly differ on the mean baseline or on-trial changes in endometrial thickness. Of the 103 placebo-treated participants, 7 (6.8%) underwent endometrial biopsy; 6 (85.7%) of these biopsies were benign. One woman in the placebo group was diagnosed with complex endometrial hyperplasia with atypia and underwent hysterectomy. The pathology result from this surgical operation was stage IB endometrial cancer. Of the 121 participants in the soy group, 9 (7.4%) underwent endometrial biopsy. The results were benign in all nine cases (100%). Although the rate of hyperplasia/malignancy was higher in the placebo group (14.3% vs 0%), the difference was not statistically significant.

Conclusions

Three-year ISP supplementation has no effect on endometrial thickness or on the rates of endometrial hyperplasia and cancer in postmenopausal women.

© 2013 by The North American Menopause Society

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