By: Dr. Jordan Robertson BHSc. ND RAc

The topic of green tea and breast cancer stemmed form observations that cultural groups of regular green tea drinkers appeared to have a reduced risk of breast cancer. When compared to non-tea drinkers, women who regularly drank green tea (about 3 cups per day) appeared to have an almost 20% reduction in breast cancer (1). However, when studies have tried to replicate the results by assigning women to drinking green tea, the results are not quite as clear.

Green tea may interact with breast tissue in multiple ways. Green tea blocks the interaction of xeno-estrogens from environmental PCBs, which are known triggers for breast tissue growth(2). PCBs are a well-established risk factor for breast cancer, with a dose-response effect on unwanted breast tissue proliferation. Green tea blocks the effect of PCBs on breast tissue, also in a dose dependent manner, meaning, the more GTE you are exposed to, the less action PCBs have on breast tissue. Other biomarkers for cancer risk exist, and are currently being tracked in 1000 high-risk women who are using Green Tea Extract in the Minnesota Green Tea trial(3). Preliminary results from this study show that GTE (Green tea extract) is safe at the doses prescribed, but the results are still pending. This will help us understand the role of GTE in cancer prevention, by examining the ways GTE effects markers of breast health.

To date, most studies in humans are using green tea drinking, versus GTE – which may describe the differences we see in animal and test tube models versus the studies on tea drinking. Test tube and animal studies show a reduction in breast cancer growth, cell killing and improved effect of Tamoxifen or other Aromatase Inhibitors when combined with GTE(4). These show incredible promise for human clinical trials using GTE to achieve a pharmacological dose of green tea in breast tissue.

In women who have already experienced breast cancer, regular green tea consumption appears to reduce recurrence of both stage 1 and stage 2 breast cancers (5). Heavier drinkers (>3 cups per day) have an approximate benefit of 27% reduction in recurrence when compared to non-drinkers (1). When observing women with early stage breast cancer or DCIS, we can see that even as little as 30 days of supplementation prior to surgery changes known markers of breast cancer growth, which may have short term effects on surgical margins, and long term effects on recurrence (6). Green tea affects breast cancer growth from multiple targets, including HER2(7). Vascular development and growth factors are suppressed by green tea (1), and biomarkers of even triple negative cancers are altered in favour of reduced recurrence(8).

Regular green tea drinking (>3 cups/day) should be part of every woman’s health plan to decrease exposure to environmental estrogens, and for the added benefits of weight management and cardiovascular health we consistently see with green tea. GTE may be the most appropriate way to change biomarkers of breast cancer risk in high risk women, or in women with a previous diagnosis. Dosages in studies have ranged from 100-900 mg per day of GTE, but warrents a discussion with your Naturopath. Although we see excellent safety with GTE, a small percentage of women do experience increases in liver enzymes during treatment(9). Talk to your ND about adding GTE to your health plan. Green tea may also interact with medications such as blood thinners, antidepressants and NSADs. Talk to us before combining natural products with your drug therapy.

  1. Li M-J, Yin Y-C, Wang J, Jiang Y-F. Green tea compounds in breast cancer prevention and treatment. World J Clin Oncol. 2014 Aug 10;5(3):520–8.
  2. Baker KM, Bauer AC. Green Tea Catechin, EGCG, Suppresses PCB 102-Induced Proliferation in Estrogen-Sensitive Breast Cancer Cells. Int J Breast Cancer. 2015;2015:163591.
  3. Samavat H, Dostal AM, Wang R, Bedell S, Emory TH, Ursin G, et al. 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. Cancer Causes Control CCC. 2015 Oct;26(10):1405–19.
  4. Yiannakopoulou EC. Interaction of green tea catechins with breast cancer endocrine treatment: a systematic review. Pharmacology. 2014;94(5-6):245–8.
  5. Inoue M, Tajima K, Mizutani M, Iwata H, Iwase T, Miura S, et al. Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett. 2001 Jun 26;167(2):175–82.
  6. Yu SS, Spicer DV, Hawes D, Tseng C-C, Yang CS, Pike MC, et al. Biological effects of green tea capsule supplementation in pre-surgery postmenopausal breast cancer patients. Front Oncol. 2013;3:298.
  7. Masuda M, Suzui M, Lim JTE, Weinstein IB. Epigallocatechin-3-gallate inhibits activation of HER-2/neu and downstream signaling pathways in human head and neck and breast carcinoma cells. Clin Cancer Res Off J Am Assoc Cancer Res. 2003 Aug 15;9(9):3486–91.
  8. Crew KD, Ho KA, Brown P, Greenlee H, Bevers TB, Arun B, et al. Effects of a green tea extract, Polyphenon E, on systemic biomarkers of growth factor signalling in women with hormone receptor-negative breast cancer. J Hum Nutr Diet Off J Br Diet Assoc. 2015 Jun;28(3):272–82.
  9. Dostal AM, Samavat H, Bedell S, Torkelson C, Wang R, Swenson K, et al. The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial. Food Chem Toxicol Int J Publ Br Ind Biol Res Assoc. 2015 Sep;83:26–35.
  10. Pianetti S, Guo S, Kavanagh KT, Sonenshein GE. Green tea polyphenol epigallocatechin-3 gallate inhibits Her-2/neu signaling, proliferation, and transformed phenotype of breast cancer cells. Cancer Res. 2002 Feb 1;62(3):652–5.