The Effect of Soy Isoflavones on Steroid Metabolism
Abstract
Objective: This study is a post-hoc analysis of steroid hormones before and after administration of pharmacological doses of soy isoflavones in a large cohort of men and women from two independent studies. Isoflavones are reported to inhibit mineralo- and glucocorticoid hormone production as well as reproductive steroids in vivo and in vitro. We focused on cytochrome P450 17α-hydroxylase (CYP17A1) which catalyses the production of dehydroepiandrosterone (DHEA), in the androgen biosynthesis pathway to elucidate effects on sex steroids in vitro. Design and Setting: Effects of soy isoflavones on steroid levels in two studies comprising 400 patients were examined: 200 men (study 1; 3 months duration) and 200 postmenopausal women (study 2; 6 months duration), randomized to consume 15 g soy protein with 66 mg isoflavones (SPI) or 15 g soy protein alone without isoflavones (SP) daily. Effects of genistein and daidzein on steroid metabolism were determined in vitro, in HEK293 cells expressing CYP17A1 and in the human adrenocortical carcinoma H295R cell model. Results: SPI decreased serum dehydroepiandrosterone sulfate (DHEAS) levels in both men and women (P < 0.01), with decreased androstenedione (A4) (P < 0.01) in women not observed in men (P < 0.86). Cortisol, cortisone, 11-deoxycortisol, aldosterone, testosterone (T), or estradiol (E2) levels were unchanged. The dual hydroxylase and lyase activity of CYP17A1, which catalyses the biosynthesis of androgen precursors, and…
How strong is the evidence?
Evidence Hub reads this as a randomized trial, done in people. Its evidence level is 2 of 5 (High · randomized trial). Randomized trials of a reasonable size are the strongest single-study design. Reported size: 400 participants or records.
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