Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis

Abstract

BACKGROUNDHormonal effects of soy and isoflavones have been investigated in numerous trials with equivocal findings. We aimed to systematically assess the effects of soy and isoflavones on circulating estrogen and other hormones in pre- and post-menopausal women.METHODSThe Cochrane Library, MEDLINE and EMBASE (plus reviews and experts) were searched to December 2007. Inclusion of randomized or residential crossover trials of soy or isoflavones for 4 or more weeks on estrogens, SHBG, FSH, LH, progesterone and thyroid hormones in women was assessed independently in duplicate. Six percent of papers assessed were included. Data concerning participants, interventions, outcomes, potential effect modifiers and trial quality characteristics were extracted independently in duplicate.RESULTSForty-seven studies (11 of pre-, 35 of post- and 1 of perimenopausal women) were included. In premenopausal women, meta-analysis suggested that soy or isoflavone consumption did not affect primary outcomes estradiol, estrone or SHBG concentrations, but significantly reduced secondary outcomes FSH and LH [by ∼20% using standardized mean difference (SMD), P = 0.01 and 0.05, respectively]. Menstrual cycle length was increased by 1.05 days (95% CI 0.13, 1.97, 10 studies). In post-menopausal women, there were no statistically significant effects on estradiol, estrone, SHBG, FSH or LH, although there was a small statistically non-significant increase in total estradiol with soy or isoflavones (∼14%, SMD, P = 0.07, 21 studies).CONCLUSIONSIsoflavone-rich soy products decrease FSH and LH in premenopausal women and may increase estradiol in post-menopausal women. The clinical implications of these modest hormonal changes remain to be determined.

Soy, phytoestrogens and their impact on reproductive health

“…There have been reports in humans which reveal a modest suppressant effect of soy and isoflavone exposure on the hypothalamic-pituitary-gonadal axis. Although available data are highly heterogeneous, a recent metaanalysis of 47 studies concluded that consumption of soy and isoflavones in premenopausal women reduces circulating LH and FSH, and increases menstrual cycle length (Hooper et al, 2009). In contrast no statistical effects were observed on hormonal status in postmenopausal women.…”

Isoflavonas de soya y salud humana: cáncer de mama y sincronización de la pubertad

“…Por el contrario, cuando las ratas fueron inyectadas con estrógenos, la ingesta de ISO atenuó la acción estimuladora del estradiol sobre la expresión de la luciferasa, es decir, produjo un efecto antiestrogénico 17 . Un reciente meta-análisis de 47 protocolos sugiere que el consumo de soya o de isofl avonas, en mujeres pre o postmenopáusi-cas, no afecta los niveles circulantes de estrógenos, pero reduce signifi cativamente los niveles de FSH y LH en mujeres premenopáusicas 18 .…”

Soy Isoflavones as Bioactive Ingredients of Functional Foods

“…This chapter does not describe the effects of soy IFs on circulating levels of estrogens and other hormones in women, and the extensive review and meta-analysis of the literature to examine these effects published by Hooper et al (2009) is recommended. Since a variety of functional foods especially formulated for women are marketed considering the putative beneficial effects of IF intake on bone health and menopausal symptoms, these subjects are briefly described.…”