The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial

- Green tea may have health benefits and also cause adverse symptoms in high doses.
- The safety of green tea extract (GTE) was assessed in postmenopausal women.
- GTE was associated with higher incidence of nausea and skin-related adverse events.
- GTE was associated with higher incidence of ALT elevations compared to placebo.
- Adverse events were mainly mild and transient; GTE was generally well tolerated.

Green tea is thought to provide health benefits, though adverse reactions to green tea extract (GTE) have been reported. We conducted a randomized, double-blind, placebo-controlled study of GTE on breast cancer biomarkers, including mammographic density, in which 1075 postmenopausal women were randomly assigned to consume GTE containing 843 mg (-)-epigallocatechin-3-gallate (EGCG) or placebo daily for one year. There were no significant differences in % of women with adverse events (AEs, 75.6% and 72.8% of the GTE group and placebo group, respectively) or serious AEs (2.2 % and 1.5% of GTE and placebo groups, respectively). Women on GTE reported significantly higher incidence of nausea (P < 0.001) and dermatologic AEs (P = 0.05) and significantly lower diarrhea incidence (P = 0.02). More women in the GTE group experienced an alanine aminotransferase (ALT) elevation compared with placebo group (n = 36, (6.7%) vs. n = 4, (0.7%); P < 0.001). There were no statistically significant differences between groups in frequencies of other AEs. Overall, AEs were mainly mild and transient, indicating that daily consumption of GTE containing 843 mg EGCG is generally well tolerated by a group of predominantly Caucasian postmenopausal women. However, 6.7% of GTE consumers experienced ALT elevations, with 1.3% experiencing ALT-related serious AEs.