HealthCare

ANTICARCINOGENIC

McGill University researchers in Canada have shown in the lab that EGCG from green tea inhibits the growth of cancer cells. A Japanese study found that women with breast cancer were less likely to suffer a recurrence if they drank at least two cups of green tea daily. An analysis of 22 studies of green tea and lung cancer concluded that consuming two cups daily was associated with an 18-percent lower risk. And the Shanghai Women’s Health Study reported that participants who regularly drank green tea at the start of the study were 37 percent less likely to develop colorectal cancer over six years than those who seldom or never sipped it. Life-long green tea drinkers fared even better, with as much as a 57-percent relative risk reduction.

More recently, a 2009 review of the effectiveness of green tea in the prevention of cancers found that much of the evidence was inconclusive. “In selected areas,” however, “green tea was effective in slowing the progression of the earlier stages of cancer.”

Green tea extract (GTE) associated anticancer activity in cell lines – such as urothelial and lung adenocarcinoma lines – have been reported; however, the direct effect of GTE on metastatic or normal cells from clinically obtained human samples had not been studied before.
Several in vitro studies have shown a dose-dependent decreased proliferation and/or increased apoptosis in a variety of cancer cell lines (lung, prostate, colon, stomach, oral, leukaemia and breast) . Additionally, photo chemopreventative effects for green tea and epigallocatechin gallate have been demonstrated in vitro, in vivo and on human skin.
The mechanism of action by which tea polyphenols exert antimutagenic and
antitumorigenic effects is still largely speculative. However, the following has been observed: inhibition of the large multicatalytic protease and metalloproteinases, which are involved in tumour survival and metastasis, respectively, and inhibition of many tumour-associated protein kinases, while not affecting kinase activity in normal cells. Tea polyphenols have also been found to inhibit some cancer-related proteins that regulate DNA replication and transformation. More recently, there is increasing evidence that catechins possess antiangiogenic properties .

Clinical note— The difference between teas
Black, green and oolong tea are produced from the same plant (Camellia sinensis) but differ in polyphenol content according to the way the leaves are processed. Green tea Black tea is made from oxidised leaves whereas oolong tea is made from partially oxidised leaves and green tea leaves are not oxidised at all. Because the oxidising
process converts many polyphenolic compounds into others with less activity, green tea is considered to have the strongest therapeutic effects and the highest polyphenol content (Lin et al 2003). Caffeine concentrations also vary between the different teas: black tea > oolong tea > green tea > fresh tea leaf (Lin et al 2003).
Variation in caffeine content in green tea is further influenced by growing conditions, manufacturing processes and size of the tea leaves (Astill et al 2001). The highest quality leaves are the first spring leaf buds, called the ‘first flush’. The next set of leaf buds produced is called the ‘second flush’ and considered to be of poorer quality. Tea varieties also reflect the area they are grown in (e.g. Darjeeling in India), the form produced (e.g. pekoe is cut, gunpowder is rolled) and processing method (black, oolong or green)