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-3gallate 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 Ps 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.
Bibliographical noteFunding Information:
Supported by NIH/National Cancer Institutegrant R01 CA127236 (to MSK, Principal Investigator), Department of Defense/US Army Medical Research and Materiel Commandgrant W81XWH-11-1-0013 (to HS), NIH/National Cancer Institute training grant in cancer epidemiology T32CA186873, the University of Minnesota Graduate School Doctoral Dissertation Fellowship (to HS), and the National Center for Advancing Translational Sciences of the NIH, award number UL1TR000114. Author disclosures: HS, AHW, GU, CJT, RW, MCY, DY, MSK, and J-MY, no conflicts of interest. Supplemental Tables 1–3 are available from the “Supplementary data” link in the online posting of the article and from the same link in the online table of contents at https://academic.oup.com/jn/. Address correspondence to HS (e-mail: firstname.lastname@example.org). Abbreviations used: ALT, alanine aminotransferase; COMT, catechol-O-methyltransferase; EC, epicatechin; EGC, epigallocatechin; EGCG, epigallocatechin gallate; GTE, green tea extract; IGF, insulin-like growth factor; IGF-1, insulin-like growth factor 1; IGFBP-3, insulin-like growth factor binding protein 3; MGTT, Minnesota Green Tea Trial; SHBG, sex hormone-binding globulin; SNP, single nucleotide polymorphism; UGT, uridine diphosphate-glucuronosyltransferase.
© 2019 American Society for Nutrition. All rights reserved.
- Breast cancer
- Green tea extract
- Insulin-like growth factors
- Postmenopausal women
- Sex hormones