Green tea might cut colon cancer risk by 60%
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April 13, 2007
Filed under Uncategorized
International Health News – More good news for tea lovers. A joint study by Chinese and American scientifists have identified the specific contents in green tea that could prevent the occurrence of colon cancer by as high as 60%.
Researchers at the University of Minnesota, Rutgers and the Shanghai Cancer Institute recently reported on what they claim is the first study to examine the association between specific biomarkers of tea polyphenols and the risk of colorectal cancer in humans.
Subjects were dawn from the Shanghai Cohort Study who were between 45 and 65 years of age and had no history of cancer at recruitment. Dietary and lifestyle data was collected at enrollment and in addition, blood and urine samples were acquired and stored.
The study involved 16 years of follow-up during which 162 incident colorectal cancer cases were identified and matched with 806 controls. Levels of green tea polyphenols and their metabolites (six in total) were determined in the urine samples of cases and controls.
What are polyphenols? Polyphenols are a group of chemical substances found in plants. Research indicates that polyphenols may have antioxidant characteristics with potential health benefits. They may reduce the risk of cardiovascular disease and cancer. Polyphenols have also been investigated as a source of additional health benefit in organic produce, but no conclusion was made. It is believed that polyphenols can bind with nonheme iron (from plant sources) and decrease its absorption by the body.
What are tea polyphenols? According to the National Cancer Institute, tea polyphenols are compounds in tea leaves that are natural plant antioxidants. Antioxidants have been shown to prevent damage caused by free radicals to DNA and other molecules.
Tea polyphenols have demonstrated several cancer preventive properties. In addition to antioxidant activity, these compounds may reduce abnormal cell growth and inflammation; help the body get rid of cancer-causing agents; and restore communication between different cells in the body.
The relationship between tea consumption and human cancer has been studied in several different populations and at various cancer sites. Some of the studies comparing tea drinkers to non-tea drinkers support the claim that tea-drinking prevents cancer, others do not. Dietary, environmental, and population differences may account for these inconsistencies.
In animal studies, different tea extracts, tea polyphenol mixtures, purified tea components, and tea infusions as the sole drinking fluid have more consistently been shown to prevent cancer, including cancers of the colon, esophagus, liver, stomach, lung, breast, pancreas, and skin.
The purified component, epigallocatechin gallate (EGCG), prevented colon cancer, but did not prevent cancer of the esophagus in animal models. A polyphenol mixture with EGCG, called Polyphenon E, has also shown cancer preventive properties in animals. Animal studies were inconclusive as to whether EGCG or Polyphenol E caused DNA mutations that might trigger cancer growth. Both EGCG and Polyphenon E are being tested for safety and efficacy in humans.
In the present study, the results were stratified by quartiles or tertiles of polyphenol levels and colon, rectal and the risks for colorectal cancer were determined. Significant results were obtained for two polyphenols, epigallocatechin (EGC) and 4’-0-methyl-epigallocatgechin (4’-MeEGC) and only for colon cancer.
For EGC, compared to undetectable levels, a 60% risk reduction was found for the highest urine level, and almost the same risk reduction was seen when the first vs. 4th quartile of 4’-MeEGC were compared or when the two polyphenol levels were combined.
These results were consistent with epidemiologic data on green tea intake and colon cancer where a 26% risk reduction was found. The authors briefly discuss possible mechanisms including the potential for tea polyphenols to protect against the carcinogenic activity of heterocyclic aromatic amines.
[Yuan, J.-M. Urinary Biomarkers of tea Polyphenols and Risk of Colorectal Cancer in the Shanghai Cohort Study., International Journal of Cancer, 2007, Vol. 120, pp. 1344-50.]