A pilot study of the effects of phytoestrogen supplementation on postmenopausal endometrium.

Objective: This study was designed to assess endometrial histology in postmenopausal women not taking hormone replacement therapy, to evaluate side effects and efficacy of phytoestrogens in treating menopause-associated symptoms, and to determine whether 6 months of phytoestrogen supplementation altered endometrial histology.

Methods: We performed a prospective, double-blinded, randomized, placebo-controlled trial comparing the effects of 6 months of dietary phytoestrogen supplementation versus placebo in postmenopausal women. Baseline endometrial biopsies were performed and, if adequate, nonhyperplastic, noncancerous, and nonovulatory, subjects were randomly assigned to receive daily placebo or soy cereal supplementation for 6 months. Study subjects completed baseline and weekly dietary, symptom, and side effect logs. Repeat endometrial biopsies were obtained at 6 months.

Results: Subjects were recruited from January 1998 through June 2000. Twenty-seven subjects were randomized, and 19 completed the study. One (3.7%) baseline endometrial sample was weakly proliferative. All other baseline and final biopsies were consistent with atrophic, inactive endometrium. The maximum risk of endometrial stimulation with phytoestrogens is 35%. Hot flushes, night sweats, and vaginal dryness were significantly less severe at the final week of the study compared with baseline in the placebo group. Insomnia was more common in the treated group. There were no other statistically significant differences in symptoms or side effects.

Conclusion: Phytoestrogens did not cause stimulation of the endometrium. Insomnia was more frequent over the 6-month study in the soy group, whereas hot flushes, night sweats, and vaginal dryness improved from baseline in the placebo group but not in the soy group.