It is the most commonly consumed beverage in the world. Black tea consumption is prevalent in Northern Europe, North America, and Western Asia, while green tea consumption is more common in Eastern Asia (Oh et al. 2015). Tea contains polyphenols and other components which have been described as antiestrogenic, antiangiogenic, antiapoptotic, antioxidant, prooxidant, and tumor inhibitory, and other potentially chemopreventive properties (Shrubsole et al. 2009). Many studies examined the association of tea intake and risk of breast cancer; however the results are contradictory (Ganmaa et al. 2008; Larsson et al. 2009; Boggs et al. 2010; Fagherazzi et al. 2011; Oh et al. 2015). In meta-analysis of 13 papers which investigated populations in 8 countries showed that the association between black tea intake and risk of breast cancer is inconsistent; a negative association was found between black tea consumption and breast cancer risk in 8 case-control studies; however in 5 cohort studies there was a moderate significant increase in breast cancer risk with black tea consumption (Sun et al. 2006). In the Swedish Mammography cohort study, the association of black tea consumption with the incidence of overall breast cancer, and study in context of estrogen receptor (ER) and progesterone receptor (PR) status of the tumor, has been investigated. The findings of this study suggest that black tea consumption may increase the risk of ER+/PR+ tumors (Larsson et al. 2009). The Swedish Women’s Lifestyle and Health study showed that tea consumption is positively associated with the risk of overall and ER+/PR+ breast cancer (Oh et al. 2015). No correlation between tea drinking and overall breast cancer risk was observed in the Nurses’ Health Study (Ganmaa et al. 2008), in the Black Women’s Health Study (Boggs et al. 2010), and in French cohort study (Fagherazzi et al. 2011) . Anticancer effect of crude green tea extract was studied on 472 patients with I– III stages of breast cancer for 7 years. The results showed that increased consumption of green tea reduced the number of axillary lymph node metastases in premenopausal patients with stage I and II. Further, increased green tea intake was linked with reduced relapse of stage I and II breast cancer (Nakachi et al. 1998). Similarly, in another meta-analysis investigation, it was shown that there is an inverse relationship between intake of green tea and breast cancer risk (Sun et al. 2006). The anti-breast cancer effect of green tea extract with tamoxifen was investigated in vitro and in vivo. The study showed that green tea extract increased tamoxifen-induced antiproliferation in ER+ MCF-7, T47D, and ZR75 human breast cancer cells in vitro. Further, the mice treated with the combination of green tea extract + tamoxifen had decreased tumor size and more apoptosis in tumor tissue as compared to the mice treated with either agent alone (Sartippour et al. 2006). Another large population-based case-control research performed in Shanghai showed that green tea intake may be weakly correlated with a reduced breast cancer risk. However in one study, the relationship between green tea intake and incidence of breast cancer remained unclear (Ogunleye et al. 2010).
