The effects of soy protein containing phytoestrogens on menopausal symptoms in postmenopausal women

Abstract

Objective To analyze the impact of soy protein dietary supplements containing phytoestrogens on menopausal symptoms in healthy postmenopausal women. Methods A double-blind, placebo-controlled trial was conducted in 94 healthy postmenopausal women aged 50–75 years, with 44 randomized to soy supplements containing 118 mg of isoflavones (daidzein, genistein, glycitein and their respective glycosides), and 50 to an identically presented casein placebo. A validated questionnaire on menopausal symptoms was administered at baseline and at 3 months of treatment. Compliance was assessed by high-performance liquid chromatography assay of urinary phytoestrogens. Statistical analysis was completed using non-parametric statistical methods and multivariate analysis. Results At baseline 80% of women recruited were experiencing menopausal symptoms, although symptom severity was mild. Those consuming phytoestrogen supplements had 13- and 17-fold increases in urinary excretion of genistein and daidzein, respectively, with no change in the placebo group. Active soy supplements did not significantly alter either individual symptoms or specific symptom category scores when compared to placebo. Within-group comparisons revealed that the active group reported a significant improvement in vaginal dryness (p = 0.01), libido (p =0.009), facial hair (p = 0.04) and dry skin (p =0.027). However, similarly, those on placebo reported an improvement in libido (p =0.015), facial hair (p = 0.014) and dry skin (p = 0.011) but not vaginal dryness. Conclusions In this group of 94 older postmenopausal women with a high frequency of mild menopausal symptoms, 3 months of soy supplements containing phytoestrogens did not provide symptomatic relief compared with placebo.