Green Tea Extract: Cure For Prostate Cancer?
Tea - consumed in Asia since ancient times - is now a popular beverage consumed worldwide, second only to water. Depending on the manufacturing process, tea can be classified as green, black and Oolong - all of which are harvested from the leaves and buds of the same plant, Camellia sinensis. Differences in production methods change each tea's chemical composition and levels of oxidation, which is why they taste and smell so unique.
The possible beneficial effects of green tea in the prevention of cancer as well as cardiovascular, neurodegenerative, and other diseases have been studied extensively. Most of these beneficial properties of green tea are thought to be because it contains a group of plant chemicals called polyphenols, which include the catechins - known to be strong antioxidants - although exactly how they act to benefit our health remains unclear at present. Still, many health-supplement companies are producing green tea extracts due to these widely recognized health benefits.
Catechins are the main type of flavonoids found in growing tea leaves, making up roughly 15-25% of the dry weight of fresh tea. Total catechin content varies depending on clonal variation, growing location, season, light variation and altitude. Tea catechins are present in relatively high levels in green tea and Oolong tea, but black tea has very little due to its preparation method. Green tea, which accounts for 20% of world tea consumption, is not fermented but directly prepared by pan frying or steaming tea leaves. Approximately one-third of a typical cup of green tea, brewed with 2.5 g tea leaves in 250 mL hot water, is made up of catechins. Of these, epigallocatechin-3-gallate (EGCG) is the most abundant, accounting for 50-75% of the total and has been studied in great detail in terms of its health potential.
Many studies suggest that green tea consumption may protect against heart disease and some types of cancer, including prostate cancer. Clinical trials designed to study whether green tea is useful in treating prostate cancer are ongoing, although still in the early stages. At present, there is not enough evidence to confirm that green tea is effective in treating prostate cancer - however, laboratory and animal research on the effects of green tea in prostate cancer have been promising.
For example -
- EGCG has been shown to block the stimulating effect of androgen (male sex hormone) on human prostate tumor cells, slowing their growth and spread and increasing the rate at which they die. Mice implanted with prostate cancer cells and injected with EGCG had lower levels of proteins needed for androgen activity, again suggesting that EGCG blocks the effects of androgen on tumor cells.
- Human prostate cancer cells pre-treated with EGCG were less likely to die when exposed to radiation than cells not treated with EGCG before radiation.
- Green tea polyphenols may exert their anti-cancer effect at least partly by blocking enzymes called histone deacetylases that are found in large amounts in prostate cancer cells.
- Mice bred to develop prostate cancer that were given water treated with green tea catechins (comparable to a human drinking 6 cups of green tea daily) for 24 weeks did not develop prostate cancer but only developed prostatic lesions - in other words, green tea catechins delay development of prostate cancer. In a related study, EGCG treatment was seen to prevent lesions in mice that began treatment at 12 weeks of age but not in those that began treatment at 28 weeks of age.
- Similarly, mice given polyphenols in drinking water starting at different ages to match different stages of prostate cancer were tumor-free longer than water-fed mice, and mice that consumed green tea the earliest benefitted the most. As measured by MRIs over time, tumor development was delayed and tumor growth was slower in the polyphenol-fed mice compared to water-fed mice. Further, polyphenols caused high levels of cell death, possibly limiting cancer spread to other parts of the body.
Some population studies and clinical trials on humans have also been done to find out if green tea can be used to prevent or treat prostate cancer. A review of population studies showed mixed findings about the effects of green tea on prostate cancer risk, although they indicate that green tea may protect against prostate cancer in Asian populations.
- 60 men with high-grade prostatic neoplasia were treated with green tea catechin capsules for one year. Overall, 9 men in the control group were diagnosed with prostate cancer compared to 1 man in the green tea catechin group, suggesting that green tea catechins lowers risk of prostate cancer in patients at high risk for the disease. A two year follow-up showed that this effect was long-lasting - a larger, multicenter trial is presently underway.
- Patients scheduled to undergo radical prostatectomy were given green tea, black tea or soda five times daily for 5 days. Tea polyphenols were found in prostate tissue samples of patients who drank either green tea or black tea. Also, prostate cancer cells treated with blood taken from patients after they drank tea grew and divided more slowly than cells treated with blood taken from patients before they drank tea.
- A small group of patients already having prostate cancer that did not respond to hormones were given capsules of green tea extract for up to 5 months. While green tea treatment was well tolerated by most of them, all 19 patients had disease progression within 1 to 5 months. Similarly, other findings suggest that green tea may have limited benefits in patients with advanced prostate cancer.
Side effects with green tea supplements were generally mild, with the most frequently reported including headache, nausea, abdominal pain, diarrhea, upset stomach, dizziness and weakness. Green tea was generally well tolerated in clinical studies of patients with prostate cancer. The most commonly reported side effects of green tea were gastrointestinal symptoms which were usually mild, occurring most often in patients taking the drug on an empty stomach and at the highest doses.
Various green tea extracts taken orally have been linked with liver damage in recent years, mostly in women taking green tea extract for weight loss. Most patients recovered within 4 months after stopping the green tea extract. At present, the FDA has not approved the use of green tea as a treatment for cancer or any other medical condition and recommends that green tea supplements should be taken with food by patients in clinical trials and that liver function tests should be done during treatment.