Perhaps you are already a connoisseur of green tea, or perhaps you are already aware of the many health benefits, including the area of breast cancer risk reduction and recurrence. Based on a study 
some years back, I have been advising women with stage I and II breast cancer to drink 5 cups/day or take a select number of capsules per day (amount is based on the dose per capsule ). This meta-analysis is a good update on the topic. The purpose of this systematic review and mata-analysis was to evaluate green tea consumption and breast cancer risk, recurrence and risk in relationship to menopause status.
A literature search was done following current Systematic Review and Meta-Analysis guidelines, and using 3 search systems (PubMed, Scopus, and the Web of Science). Observational studies that evaluated breast cancer risk in adult women were included and selected studies evaluated green tea consumption using a questionnaire or interview. A total of 194 studies were detected but of those 39 were duplicate studies and 115 did not meet the inclusion criteria; Another 25 studies were excluded because there was insufficient differentiation between the kind of teas that were consumed and 2 studies were excluded due to data insufficiencies. That left 13 studies that were included in this meta-analysis. Seven were conducted in Japan, five in China and one in the U.S.
Seven of these studies analyzed breast cancer recurrence in women with a previous history, and six studies followed healthy women to determine breast cancer risk. Three of the seven studies on breast cancer recurrence showed a possible protective effect of consuming green tea. The remaining four did not find a statistically significant correlation. Of the other six studies analyzing the risk of breast cancer, none of them showed a statistically significant effect. The potential benefit that was seen in those studies that reported five cups of green tea per day.
In addition to these findings, an analysis was also done comparing the risk of breast cancer in women before and after menopause and the influence of green tea. A statistically significant protective effect of green tea was seen in pre-menopausal women while no protective effect was seen in postmenopausal women. The protective effect in the overall meta-analysis, was a 15% reduction in breast cancer risk. There was also a significant reduction in breast cancer recurrence in the majority of the cohort studies but not in the case-control studies. Green tea was not associated with the risk of a new breast cancer diagnosis in those case-control studies, but conversely, green tea consumption significantly reduced breast cancer recurrence by 19%.
Commentary: One of the limitations of this meta-analysis was that the amount of green tea consumption varied with some studies reporting in grams and others in cups, and the serving size ranged from 100 mL to 350 mL. In addition, diet, other lifestyle factors and cultural differences were not considered. There is also insufficient information about breast cancer staging and what stage and receptor markers might be more influenced by green tea and breast cancer recurrence. None the less, green tea, for risk reduction, at least in pre-menopausal women, and breast cancer recurrence reduction, in at least stage I-II breast cancer patients, is still good advice. For both these effects, I would encourage approximately 3-5 cups per day which is often equal to 1-2 capsules per day of a green tea extract containing 330 mg of green tea leaf extract if it contains 98% polyphenols, 80% catechins, and 45% EGCg (epigallocatechin gallate) .
Reference: Gianfredi V, Nucci D, Abalsamo A, et al. Green tea consumption and risk of breast cancer and recurrence- A systematic review and meta-analysis of observational studies. Nutrients. 2018 December;10(12):E1886.
