Green tea - a miracle medicine?
Evidence for the manifold benefits of green tea continues to mount. A study of nearly 70,000 Chinese women showed a significant reduction in the risk of developing colorectal cancer in women who drank green tea regularly, with the greatest reduction among those who drank more tea overall and who drank it regularly. (Prospective cohort study of green tea consumption and colorectal cancer risk in women. Cancer Epidemiol Biomarkers Prev 2007; 16: 1219-23).
In another study of over 50,000 Japanese adults (40-79 years of age), women who drank from one to five or more cups of green tea a day showed a 40-70% reduced risk of developing oral cancer (depending on the amount of green tea consumed). No such benefit was demonstrated for men. (A prospective study of green tea consumption and oral cancer incidence in Japan. Ann Epidemiol. 2007 Oct;17(10):821-6).
Another large Japanese study which followed nearly 50,000 men (40-69 years old) for 14 years, found that drinking five cups of green tea a day was associated with a reduction of 48% of developing advanced prostate cancer. The study did not find an association between green tea intake and earlier stage (localised) prostate cancer, however. Green tea consumption and prostate cancer risk in Japanese men: a prospective study. Am J Epidemiol. 2008 Jan 1;167(1):71-7).
Green tea’s cancer-fighting ability may stem from its high antioxidant content. These compounds can stimulate the body’s production of enzymes involved in the cellular detoxification processes that eliminate carcinogens.
In a study carried out in the USA, 42 healthy volunteers took standardised green tea extract capsules, containing 800 mg of epigallocatechin gallate (EGCG, a potential cancer-fighting antioxidant which is the major polyphenol constituent of fresh tea leaves) each day. This provided EGCG equivalent to drinking 8-16 cups of green tea daily. The researchers found that the level of activity of a group of detoxifying enzymes called glutathione S-transferases (GST) in circulating blood lymphocytes increased by 80% in the study participants who had the lowest GST levels at the start of the study. Participants with medium or high GST levels showed either no increase or a slight increase in GST levels. (Modulation of human glutathione s-transferases by polyphenon e intervention. Cancer Epidemiol Biomarkers Prev. 2007 Aug;16(8):1662-6).
Green tea extract also appears to be a promising treatment for skin disorders such as psoriasis. In this condition, skin cells multiply out of control, causing the skin to thicken and flake off. Human psoriatic tissues lack normal expression of caspase 14, an enzyme associated with epithelial cell differentiation and programmed cell death. American researchers divided mice with a genetic predisposition for psoriasis into two groups, one group was bathed routinely in warm water and one in a green tea extract (again consisting of EGCG) mixed with water.
They found that the mice bathed in the green tea extract developed smaller, less inflamed skin lesions at a slower rate than the mice washed with water alone. The green tea appeared to slow down the production of skin cells by regulating the activity of caspase 14. The treatment may also work for other similar skin lesions such as dandruff and those induced by lupus. (Green tea polyphenol induces caspase 14 in epidermal keratinocytes via MAPK pathways and reduces psoriasiform lesions in the flaky skin mouse model. Exp Dermatol. 2007 Aug;16(8):678-84).
EGCG has also proved to be able to save mice from lethal bacterial sepsis. The pathogenesis of sepsis is in part due to bacterial endotoxin, which stimulates macrophages to release pro-inflammatory cytokines including HMGB1 (high mobility group box 1). An American group gave EGCG to mice suffering from severe sepsis, at a dose equivalent to ten cups of green tea in a human. Survival rose from 53% in those that did not receive green tea extract to 82% in those who did. The extract’s effects are thought to be due to suppression of HMGB1-mediated inflammatory responses. (A Major Ingredient of Green Tea Rescues Mice from Lethal Sepsis Partly by Inhibiting HMGB1. PLoS ONE. 2007 Nov 7;2(11):e1153).
And finally, EGCG has also been shown to have neuroprotective effects. When mice with Parkinson’s disease were administered EGCG (equivalent to 2-4 cups of green tea per day) by Israeli scientists, not only was further deterioration of their brain cells prevented, but already damaged neurons were also regenerated. This work is the first to suggest that such an inexpensive and readily available household product as green tea can be used for ‘neurorescue’. (Multifunctional Neuroprotective Activities of Green Tea Polyphenols. Fourth International Scientific Symposium on Tea and Human Health, September 2007).