Samavat, Hamed2016-10-252016-10-252015-08https://hdl.handle.net/11299/182763University of Minnesota Ph.D. dissertation. August 2015. Major: Nutrition. Advisor: Mindy Kurzer. 1 computer file (PDF); xii, 322 pages.Objective: To investigate the effects of daily intake of a highly concentrated green tea extract (GTE) for one year on circulating sex hormones and insulin-like growth factor (IGF) proteins as well as urinary estrogens and estrogen metabolites in postmenopausal women with different catechol-O-methyltransferase (COMT) genotypes. Method: The Minnesota Green Tea Trial (MGTT) is a randomized, double-blind, placebo-controlled, phase II clinical trial. Healthy postmenopausal women with heterogeneously or extremely dense breast tissue (age = 59.78 ± 5.02 years; body mass index= 25.70 ± 8.21 kg/m2) were randomly assigned to the GTE group (n=538) and were given 4 capsules a day, each containing 200 mg epigallocatechin gallate (EGCG) and the others (n=537) to the placebo group. Participants were 93% non-Hispanic white and non-current hormone users. Twenty-four hour urine samples were collected at month 0 and at the end of the study, and fasting blood samples were drawn at months 0, 6 and 12. Circulating and urinary estrogens, as well as urinary estrogen metabolites were quantified by the liquid chromatography-tandem mass spectrometry method. Blood IGF axis proteins were analyzed by ELISA. Results: GTE supplementation was associated with reduced urinary estriol levels (P= 0.02) and higher urinary 2-hydroxyestrone (P= 0.02) compared to the placebo. There was also less of a reduction in the urinary levels of 16α-hydroxyestrone in the GTE versus placebo group. Intake of the GTE resulted in significant increase of circulating estradiol and testosterone and their corresponding free and bioavailable fractions, whereas these measures were reduced in the placebo group. Additionally, COMT genotype did not modify the GTE effect on either circulating sex hormones and IGF proteins or urinary estrogens. Conclusion: Daily intake of high-dose of green tea extract for 12 month exerts modest effects on urinary excretion of estrogen metabolites, yet these effects are not modified by the COMT polymorphisms. Potential breast cancer protective effects of GTE are not mediated by alterations in circulating sex hormones or IGF axis proteins.enBreast cancerGreen teaPostmenopausal womenSex hormonesThesis or Dissertation