DR. T.S. SARAVANAN
|Catechins in green tea are novel biocompounds with multifarious health benefits.|
Protective effects: Preparing green tea in Japan.
GREEN tea is a perennial shrub belonging to the family Camellia, native to the mountainous southwest of China. Teas are usually categorized into two types: Chinese (Variety Sinensis) and Assam (Variety Assamica). All teas come from leaves that are picked and processed from the same type of tree. The specific method of processing differentiates the various types of teas into green, black, and oolong tea.
In preparing green tea, the leaves are dried but not fermented. Commercially prepared green tea extracts contain 60 per cent polyphenols.
Good for health
There are four primary polyphenols in green tea and they are often collectively referred to as catechins. As powerful antioxidants, catechins have been shown in recent studies to fight viruses, slow aging, antiproliferative effect on cancer cells and also have other beneficial effect on health.
Clinical tests have shown that catechins destroy free radicals and have far-reaching positive effects on the entire body. The free radicals are highly reactive molecules that can damage the body at the cellular level leaving the body susceptible to cancer, heart disease and many other degenerative diseases.
Recent research findings suggest that green tea confers protective effects against many cancers.
The incidence of prostate cancer, for example, is the lowest in China and Japan, countries with high green tea consumption. Risk of oesophageal cancer was reduced by 60 per cent in those who consume two to three cups of green tea daily in China. A prospective cohort study of 8,552 Japanese found a significant inverse relationship between green tea consumption and cancer incidence.
Females consuming more than 10 cups of green tea daily had the most notable protection, compared with those consuming less than three cups per day.
Green tea consumption has also been associated with a better outcome in some with breast cancer. Higher intake of green tea (mean: eight cups a day) is associated with a significantly reduced recurrence rate and a longer disease-free period, particularly among pre-menopausal women with histologically classified stage I and II breast Cancer. Among the specific green tea related benefits noted in patients were decreased numbers of axillary lymph node metastases.
Further, Epigallocaechin-3-gallate (EGCG) especially has shown marked anti-cancer effects against breast, colon, prostate, pancreatic, skin, bladder, lung, stomach, ovarian, leukaemia and liver cancer.
ECGC has also been shown to induce apoptosis in several of these cancer types while leaving normal cells unaffected and also shown to inhibit urokinase, a proteolytic enzyme often required for cancer growth, angiogenesis and androgen activity in prostate cell line. Very recently ECGC has been shown to be more effectively suppress the growth of prostate cancer and epithelial ovarian cancer cell lines derived from tumours of patients with different stage of disease.
Heart and cholestrol
The incidence of cardiovascular disease in China is about 80 per cent lower than in developed countries. This has been associated with the high consumption of green tea.
Numerous epidemiological studies have also associated high intake of green tea with decreased risk of atherogenesis in Japan.
In nitro and animal studies have shown that green tea and its catechins, especially EGCG, can help prevent oxidation of LDL-cholesterol. Recently, a human study demonstrated that EGCG inhibits phospholipids hydroperoxidation in plasma.
Mixed results have been reported on the ability of green tea to significantly reduce LDL-cholesterol oxidation in humans in that daily consumption of seven to eight cups of green tea might reduce LDL-cholesterol oxidation to an extent reduce the risk of cardiovascular disease.
In Japan, researchers have found that green tea may protect the ageing brain, as regular consumption means lesser risk of mental decline due to age.
Further, a study of 1003 70-year-old adults revealed that those who drank two or more cups a day were about half as likely to show cognitive impairment as those who drank three cups or less each week. Men and women who averaged one cup per day fell somewhere in between.
In addition, catechins have exhibited a variety of anti-inflammatory effects, raising hopes that they might be helpful in treating some forms of arthritis, dermatosis, gout and other inflammatory conditions.
Green tea also has thermogenic properties and promotes fat oxidation. There is in vitro evidence that green tea and its catechins have some antiviral and other antimicrobial activities.
Recently various green tea catechins were shown to inhibit extracellular release of vero toxin from enterohemorrhagic E. coli.
The writer has carried out research on green tea catechins at John Wayne Cancer Institute at Santa Monica, Los Angeles, California.