In a recent article in the Journal of Agricultural and Food Chemistry, Kaur et al., presented their research on the effect of green tea catechins (GTC) and black tea theaflavins (BTT) on the occurrence of breast cancer in mice.
From the introduction:
Epidemiological evidence suggests that breast cancer is preventable as its incidence is lower in Japan and China than in the US. Additionally, Western countries have a 4x increased incidence than less industrialized nations. The recurrence of breast cancer was especially low in Japanese women who drank daily three or more cups of green tea. The epidemiological evidence of for black tea is less conclusive but black tea extracts have prevented breast cancer in rodents.
The active ingredient for green tea is thought to be the catechin epigallocatechin-3′-gallate (EGCG). During fermentation, catechins undergo enzymatic oxidation to form theaflavins and thearubigins.
The objective of the study was to investigate the effect of GTC and BTT on the life span and formation of breast cancer in both wild type and breast cancer experimental (BCE) mice. BCE mice are breed to be more susceptible to breast cancer than wild type mice. The tea extracts contained:
Green tea extract (GTC)…was comprised of 95% polyphenols including 3% epicatechin, 10% epigallocatechin, 5% epicatechin-3-gallate and 60% epigallocatechin -3′-gallate. Black tea extract (BTT)… contained 11% theaflavin, 28% theaflavin-3-gallate, 16% theaflavin-3′-gallate and 45% theaflavin-3,3′-digallate. The caffeine contents of GTC and BTT were < 0.5% and 0, respectively.
Female mice were given either plain drinking water (control) or drinking water with either GTC or BTT at 0.01 or 0.05 % (w.v) (treatment groups). The intake of GTC or BTT had no effect on fluid or food consumption. BCE Mice in the higher level treatment groups lived longer than control BCE mice and there was also a slight but insignificant reduction in the number and size of tumors. The consumption of the lower level of tea extracts (0.01 %) had no effect on mammary carcinogenesis.
In a study where mice were killed at the same age of 19 weeks, tumor development was reduced by the consumption of tea extracts, but only tumor volume was significant reduced by tea consumption.
The study considered the extent of apoptosis (programmed cell death) and the extent of lipid oxidation, which is thought to be one of the mechanisms, in the mammary tissues of the mice. In treatment mice indicators for apoptosis were higher and indicators of lipid oxidation were lower than in control mice.
In conclusion, GTC and BTT decreased both the incidence and size of mammary tumors, with GTC being more effective than BTT. Both tea extracts also decreased the extent of lipid oxidation, which fits with the proposed antioxidant effects of catechins. Finally, both GTC and BTT increased the extent of apoptosis. So extracts from green tea and black tea may be important dietary factors limiting the incidence of human breast cancer.
Kaur, S., Greaves, P., Cooke, D.N., Edwards, R., Steward, W.P., Gescher, A.J. and Marczylo, T.H. “Breast Cancer Prevention by Green Tea Catechins and Black Tea Theaflavins in the C3(1) SV40 T,t Antigen Transgenic Mouse Model Is Accompanied by Increased Apoptosis and a Decrease in Oxidative DNA Adducts” J. Agric. Food Chem.,ASAP Article 10.1021/jf0633342 S0021-8561(06)03334-6: Web Release Date: April 4, 2007 link (subscription required)
Wikipedia info on Green Tea
Wikipedia article of apoptosis (very informative).