The Minnesota Green Tea Trial (MGTT), a randomized controlled trial of the efficacy of green tea extract on biomarkers of breast cancer risk: study rationale, design, methods, and participant characteristics

Abstract

Purpose The Minnesota Green Tea Trial (MGTT) was a randomized, placebo-controlled, double-blinded trial investigating the effect of daily green tea extract consumption for 12 months on biomarkers of breast cancer risk. Methods Participants were healthy postmenopausal women at high risk of breast cancer due to dense breast tissue with differing catechol-O-methyltransferase (COMT) genotypes. The intervention was a green tea catechin extract containing 843.0 ± 44.0 mg/day epigallocatechin gallate or placebo capsules for one year. Annual digital screening mammograms were obtained at baseline and month 12, and fasting blood and 24-hour urine samples were provided at baseline, months 6, and 12. Primary endpoints included changes in percent mammographic density, circulating endogenous sex hormones and insulin-like growth factor axis proteins; secondary endpoints were changes in urinary estrogens and estrogen metabolites and circulating F2-isoprostanes, a biomarker of oxidative stress. Results The MGTT screened more than 100,000 mammograms and randomized 1075 participants based on treatment (green tea extract vs. placebo), stratified by COMT genotype activity (high COMT vs. low/intermediate COMT genotype activity). 937 women successfully completed the study and 138 dropped out (overall dropout rate= 12.8%). Conclusions In this paper we report the rationale, design, recruitment, participant characteristics, and methods for biomarker and statistical analyses.

Effects of green tea catechin extract on serum lipids in postmenopausal women: a randomized, placebo-controlled clinical trial

“…Participants showed excellent compliance, taking, on average, 96.5% of their prescribed supplements. This was confirmed by analysis of urinary catechin content in a random subsample of participants (15), by which participants in the GTE group showed a .10-fold increase in the urinary concentrations of EGC and EC compared with the placebo group. Taken together, supplementation with GTE for 12 mo was shown to significantly reduce TC, LDL cholesterol, and non-HDL cholesterol in postmenopausal women.…”

“…The current trial is a substudy of the Minnesota Green Tea Trial (MGTT), which was previously described in detail elsewhere (15). Briefly, the MGTT was a double-blind, placebo-controlled, randomized clinical trial (clinicaltrials.gov; NCT00917735).…”

“…Results for catechin compositions of capsules were similar between the 2 laboratories. A detailed description of catechin and caffeine composition of the treatment and placebo capsules was presented previously (15). GTE capsules were decaffeinated with ,4 mg caffeine/ capsule and, on average, provided 1315 mg catechins/d, including 843 mg EGCG, 202 mg epicatechin gallate, 107 mg EGC, and 107 mg EC.…”

Long-Term Supplementation of Green Tea Extract Does Not Modify Adiposity or Bone Mineral Density in a Randomized Trial of Overweight and Obese Postmenopausal Women

“…The Minnesota Green Tea Trial (MGTT) was a randomized, parallel-arm, double-blinded, placebo-controlled study designed to examine the effect of GTE on breast cancer risk factors, including obesity. Details of the study design, eligibility criteria, randomization, blinding, study conduct, and patient flow through the trial have been previously published (23). Briefly, postmenopausal women aged 50 to 70 y and classified as having high breast density (a breast cancer risk factor) were recruited from 2009 to 2013 at clinical centers in the Minneapolis-St. Paul metropolitan area.…”

Green Tea and Its Extracts in Cancer Prevention and Treatment

“…Samavat et al [165] have proposed a clinical study called the Minnesota Green Tea Trial (MGTT) which is designed to detect GT effects on postmenopausal womens health including cancer prevention. The layout of this large study was published in 2015, only safety data have been published [166].…”