Green Tea Catechin Extract Supplementation Does Not Influence Circulating Sex Hormones and Insulin-Like Growth Factor Axis Proteins in a Randomized Controlled Trial of Postmenopausal Women at High Risk of Breast Cancer. Issue 4 (30th March 2019)

• Record Type: Journal Article
• Authors: Samavat, Hamed; Wu, Anna H; Ursin, Giske; Torkelson, Carolyn J; Wang, Renwei; Yu, Mimi C; Yee, Douglas; Kurzer, Mindy S; Yuan, Jian-Min
• Is Part Of: Journal of nutrition. Volume 149:Issue 4(2019)
• Page Start: 619
• Page End: 627
• Publication Date: 2019-03-30
• Subjects: green tea extract -- catechins -- sex hormones -- insulin-like growth factors -- postmenopausal women -- breast cancer; Nutrition -- Periodicals; Diet -- Periodicals; 613.205
• DOI: 10.1093/jn/nxy316
• Languages: English
• ISSNs: 0022-3166

Abstract

ABSTRACT: Background: Consumption of green tea has been associated with reduced risk of breast cancer. Hormonal modulation has been suggested as one of the potential underlying mechanisms; however, it has yet to be fully elucidated in large, long-term human clinical trials. Objective: We investigated the effects of decaffeinated green tea extract (GTE) on circulating sex hormones and insulin-like growth factor (IGF) proteins. Methods: We conducted a placebo-controlled double-blind randomized clinical trial recruiting from 8 clinical centers in Minnesota. Participants were 538 healthy postmenopausal women randomly assigned to the GTE group (463 completed the study; mean age = 60.0 y) and 537 to the placebo group (474 completed; mean age = 59.7 y). Women in the GTE group orally took 4 decaffeinated capsules containing 1315 mg total catechins including 843 mg epigallocatechin-3-gallate daily for 1 y, whereas women in the placebo group took similar capsules containing no tea catechins. Blood sex hormones (estrone, estradiol, androstenedione, testosterone, and sex hormone-binding globulin) and IGF proteins (IGF-1 and IGF binding protein-3) were quantified at baseline and months 6 (for IGF proteins only) and 12, and were assessed as secondary outcomes of the study using a mixed-effect repeated-measures ANOVA model. Results: Women in the GTE group had significantly higher blood total estradiol (16%; P = 0.02) and bioavailable estradiol (21%; P = 0.03) than in the placebo group at month 12. There was a statistically significant interaction between GTE supplementation and duration of treatment on estradiol and bioavailable estradiol (both P s for interaction = 0.001). The catechol- O -methyltransferase genotype did not influence blood sex hormones before or after GTE supplementation. The circulating concentrations of IGF proteins were comparable between GTE and placebo groups at all 3 time points. Conclusion: These results suggest that a 12-mo GTE supplementation significantly increases circulating estradiol concentrations in healthy postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00917735.