The effect of grape seed extract on estrogen levels of postmenopausal women: a pilot study.

The role of estrogens in breast cancer (BC) development is widely accepted, leading to the development of selective estrogen receptor modulators and aromatase inhibitors for BC treatment and prevention. However, because of potential adverse effects, healthy women with high risk of BC are hesitant to take them. Preliminary evidence from animal studies shows that grapes may have an aromatase-inhibiting effect, decreasing estrogen synthesis and increasing androgen precursors. We conducted a randomized, double-blind, dose-finding early-phase trial on the effect of grape seed extract (GSE) on estrogen levels. Postmenopausal women who met study inclusion criteria (N = 46) were randomly assigned to daily GSE at a dose of 200, 400, 600, or 800 mg for 12 weeks. Primary outcome was change in plasma levels of estrogen conjugates from baseline to 12 weeks posttreatment. Thirty-nine participants (84.8%) completed the study. GSE in the 4 daily doses did not significantly decrease estrogen or increase androgen precursors.