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Shukla Y.
Environmental
Carcinogenesis Division, Industrial Toxicology Research Centre, Mahatma
Gandhi Marg, Lucknow 226001, India
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Dietary components that are capable of inhibiting the growth of cancer
cells without affecting the growth of normal cells are receiving
considerable attention in developing novel cancer-preventive
approaches. Tea, made from young leaves and leaf buds of the tea plant,
'Camellia sinensis', and the world's second most consumed beverage, has
received a great deal of attention both from the general public and the
scientific community because tea polyphenols are strong antioxidants ,
and tea preparations have inhibitory activity against tumorigenesis.
Besides this, the wide spread consumption of tea throughout the world
evoked the interest of the scientific community in the possibility of
its use in cancer prevention.
There are three main types of tea , all
coming from the tea plant viz. black tea (fermented,) green tea
(unfermented), or oolong tea (semi-fermented), classified based on the
methods of brewing and processing. Inhibition of tumorigenesis by green
or black tea preparations has been demonstrated in various animal
models in different organs. Various epidemiological studies
substantiate the correlation between tea consumption and cancer
prevention; however, they have not yielded clear conclusions pertaining
to the protective effects of tea consumption against cancer development
in humans. Many mechanisms have been proposed for the inhibition of
carcinogenesis by tea, including the modulation of signal transduction
pathways (including growth factor-mediated, mitogen-activated protein
kinase (MAPK)-dependent, and ubiquitin/proteasome degradation pathways
) that lead to the inhibition of cell proliferation and transformation;
induction of apoptosis of preneoplastic and neoplastic cells, and
inhibition of tumor invasion as well as angiogenesis. These mechanisms
need to be evaluated, verified and corroborated in animal models and
humans in order to gain more understanding on the effects of tea
consumption on human cancer. Because the causative factors are
different for different populations, tea consumption may affect
carcinogenesis only in selected situations rather than having the
general effect on all cancers.
Although, on the basis of many
epidemiological observations and numerous laboratory studies, it can be
concluded that tea consumption is likely to have beneficial effects in
reducing cancer risk in different populations, yet there is a need to
define the population that could benefit from tea consumption. After
careful evaluation of additional studies, it may be possible to
recommend consumption of tea polyphenols by humans. Although
considerable accumulating information provides a compelling body of
evidence for the preventive potential of tea against cancer, naturally
occurring tea polyphenols have yet to be evaluated in clinical
intervention in human trials.
Published in Asian Pacific Journal of Cancer Prevention. 2007 Apr-Jun;8(2):155-66.
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