Green Tea Consumption Reduces Risk of Type 2 Diabetes

A high intake of green tea may reduce the risk of developing Type 2 diabetes according to a study conducted at Osaka University, Japan and published in the Annals of Internal Medicine (144, 8:554-62, 2006). For five years researchers followed 17,413 individuals (6727 men and 10,686 women; 40 to 65 years of age) from 25 communities across Japan, who had no history of the disease. Researchers evaluated the relationship between consumption of green tea and other beverages and the development of Type 2 diabetes. During the five year trial 444 new cases of diabetes were diagnosed by physicians (231 men and 213 women). After adjustment for age, sex, body mass index, and other factors, consumption of green tea was found to be inversely associated with risk of developing Type 2 diabetes. Further, total caffeine intake from green tea was associated with a 33% reduced risk of developing the disease. These inverse associations were more pronounced in women and overweight men, suggesting a greater benefit in individuals at higher risk.

The active constituents in green tea are a family of polyphenols (catechins), which possess potent antioxidant activity. Tannins, large polyphenol molecules, form the bulk of the active compounds in green tea, of which catechins comprise nearly 90%. Several catechins are present in significant quantities including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). EGCG makes up 10-50% of the total catechin content and appears to be the most powerful of the catechins, with antioxidant activity about 25-100 times greater than vitamins C & E.

Research over the past 15 years has shown that green tea extract, containing EC and EGCG, has a number of significant health benefits.

EGCG in green tea may facilitate prostate cancer cell death, a process known as apoptosis. Researchers identified a gene involved in prostate apoptosis known as Clusterin and hypothesized that EGCG induces death in cancer cells but not normal cells by inducing Clusterin expression. Previous studies demonstrated that green tea catechins inhibited cancer cell growth in laboratory models and that use of green tea extract resulted in no significant side effects or adverse reactions. Researchers suggested using green tea as a prostate cancer prophylactic in men in high risk groups such as the elderly, African-Americans, and those with a family history of prostate cancer. Green tea may have other tumor inhibiting effects, particularly in epithelial cancers (skin, lung and digestive tract). Green tea extract may be antimutagenic, inhibiting chromosomal changes.

Green tea has also been shown to help reduce atherosclerosis and hypertension. One study found that high consumption (10 cups per day) of green tea is associated with decreased total cholesterol, LDL, VLDL, and triglyceride levels along with increased HDL levels. Green tea may also provide broad-spectrum antibacterial, antiviral, and anti-parasitic activity and be particularly beneficial in diarrheal conditions.