Green tea may stop colon cancer in its tracks - study

By Stephen Daniells

- Last updated on GMT

Related tags: Green tea, Cancer, Colon cancer

Green tea may stop the growth of colon tumours in their infancy,
suggests a new study using mice, but merely drinking green tea
offers no benefits against larger tumours.

If the study, published in the journal Carcinogenesis​, can be translated to humans, then this could have implications for the beverage and its extracts as a preventative against colon cancer. There are 363,000 new cases of colorectal cancer every year in Europe, with an estimated 945,000 globally. About 492,000 deaths occur from the cancer each year. "Our results suggest that green tea specifically targets initial stages of colon carcinogenesis; the time of administration of green tea is pivotal for effective chemoprevention,"​ wrote the researchers, led by Ala Issa from University of South Carolina. "Beverage levels of green tea are not likely to inhibit the progress of any large adenomas or adenocarcinomas existing prior to the tea administration,"​ they added. The results add to an ever-growing body of science linking consumption to a wide range of health benefits, including lower risk of certain cancers, increased weight loss, improved heart health, and protection against Alzheimer's. Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin. Issa and collaborators from the Medical University of South Carolina and the University of Columbia used ApcMin mice as a model for colon cancer and treated the animals with azoxymethane (AOM), a chemical that selectively induces cancer in the colon At the age of eight weeks, the mice were divided into two groups - one to receive water or a green tea solution (0.6 per cent) as the only beverage source for a further four to eight weeks. The researchers report that consumption of the green tea solution significantly inhibited the formation of new tumours in the colon, but had no effect against larger tumours. A mechanistic study indicated that green tea decreased the total levels of the early carcinogenesis biomarker beta-catenin and its downstream target cyclin D1. No effect on the cyclooxygenase-2 (COX-2) enzyme that plays a role in inflammatory responses and has been linked to cancer development. "Despite its appeal as a target for chemoprevention by green tea, inhibition of COX-2 expression seems to be achieved at concentrations far exceeding the physiological concentrations of catechins present in the green tea beverage,"​ wrote the researchers. "Therefore, inhibition of COX-2 cannot explain the vast number of epidemiological data that shows negative association between drinking green tea and the risk for cancers such as colorectal cancer,"​ they stated. Additional in vivo​ studies and human intervention trials are needed to further explore the potential benefits of green tea, but a large body of epidemiological data already indicates that the beverage and its extracts may offer significant benefits for lowering the risk of colon cancer. European demand for tea extracts is currently surging, and this has seen companies such as DSM, with its Teavigo boasting 95 per cent purity of EGCG, and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets. Source: Carcinogenesis​ Published online ahead of print, doi:10.1093/carcin/bgm161 "Green tea selectively targets initial stages of intestinal carcinogenesis in the AOM-ApcMin mouse model" ​Authors: A.Y. Issa, S.R. Volate, S.J. Muga, D.Nitcheva, T. Smith and M.J. Wargovich

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