Green Tea: Good for What Ails YouThe ancient Chinese may have known a thing or two about green tea, as illustrated in their old saying "It is better to drink green tea than take medicine." But it was a long time before modern science began discovering the wide array of health benefits of green tea.
Although both black and green tea come from the same plant, Camellia sinensis, the difference in the color of the brew arising from how the tea leaves are processed, the unfermented green tea has higher medicinal value. This is because it contains more polyphenols, naturally occurring chemical compounds that have been credited with many health benefits, than the fermented black tea. Unfermented tea leaves may contain up to 30 percent dry weight of tea polyphenols.
Studies conducted in the last 20 years or so have focused on the physiological effects of green tea, providing scientific backing for its original use as medicine. In addition to vitamins A, C and E, green tea contains large amounts of catechin that has been shown to have an effect on a wide range of conditions including cancer, heart disease, high blood pressure, diabetes, viral diseases, food poisoning, tooth decay and allergies.
Several studies have shown a link between the consumption of green tea and the reduction in the risk of cancer and heart disease. The main polyphenols in tea are catechins, which include the compound epigallocatechin-3-gallate. EGCG appears to inhibit cell growth and play a role in apoptosis, programmed cell death, which may be important in the prevention and control of cancer. Polyphenols are also potent antioxidants that help prevent cell damage and oxidation of low-density lipoprotein cholesterol, the "bad" cholesterol, by free radicals. These two functions are attributed with inhibiting arteriosclerosis, the formation of plaques in the arteries.
Surveys conducted in Japan indicate a significant reduction in the cancer death rate in tea-producing regions where residents are accustomed to drinking large amounts of tea. For example, a standardized mortality ratio for the Shizuoka prefecture, a famous tea-growing region in Japan, from the period 1969-1983, shows significantly lower values than the national average.
New research presented in the May issue of the International Journal of Cancer suggests that green tea may lower the odds of chronic gastritis that can precede cancer. In a study of more than 600 Chinese men and women, researchers found that green tea drinkers were about half as likely as non-drinkers to have stomach cancer or gastritis. In China, stomach cancer is the most common cancer among men and women.
However, it is too early to conclude that drinking green tea wards off stomach cancer. A Japanese study published in March, for example, found no link between green tea, coffee or black tea and stomach cancer in rats.
Green tea may have another positive impact on health, by controlling obesity. Speaking at the 6th International Symposium on Green Tea held recently in Seoul, Shutsung Liao, from the Ben May Institute for Cancer Research and Tang Center for Herbal Medicine Research, University of Chicago, reported that EGCG, injected into rats, can decrease blood levels of glucose, cholesterol, testosterone and growth-promoting hormones and significantly reinvigorate the appetites of treated rodents.
These findings suggest that EGCG may be useful in controlling obesity and other diseases such as diabetes, cardiovascular diseases and hormone-dependent cancers. Specifically, researchers found that rats injected with the substance showed body weight loss within one week. The report suggests that long-term green tea drinking or consumption of EGCG-containing extracts may mimic some of the effects caused by EGCG injection and may, ultimately, be beneficial to health.
In recent years, a number of scientific studies have focused on a different application of green tea - slathering it on the skin. Researchers are Case Western Reserve University in Cleveland, Ohio, say that polyphenols have been shown to prevent cancer in laboratory mice.
When EGCG was applied directly to the skin before ultraviolet B exposure, the compound prevented both inflammation and development of leukocytes, the white blood cells that play a key role in the development of cancer.
Speaking at the symposium in Seoul, Hasan Mukhtar from Case Western Reserve said that after examining the anti-inflammatory and photoprotective effects of green tea, he concluded that the use of skin care products supplemented with green tea, in conjunction with the use of sunscreens, may be an effective strategy for reducing ultraviolet radiation-induced photodamage inflammation and skin cancer.
Giving another thumbs-up for the use of green tea on skin, Chung Jin-ho, Department of Dermatology, Seoul National University College of Medicine, reported that EGCG can have photo-protective and anti-aging effects on the skin.
Just how much green tea needs to be taken to derive the reported health benefits is anything but clear. Different studies have suggested anywhere from 10 cups a day to merely two cups a day.
To date, the only negative side effect reported from drinking green tea is insomnia from caffeine. The tea contains approximately 30 to 60mg of caffeine in every six to eight ounces of tea. To avoid caffeine overdose it would be safe to keep green tea intake to four or five cups per day.
by Kim Hoo-ran