Scientists first became interested in the cancer preventative characteristics of green tea after a study in China, when they found that male smokers drinking 3 cups of green tea a day, had a 31% reduced rate of cancer than those that did not drink green tea.
A number of studies have been conducted finding benefits for many different types of cancers, including: stomach cancer, colon cancer, esophageal cancer, prostate cancer, colorectal cancer, pancreatic cancer, liver cancer, urinary bladder cancer, and breast cancer. These studies included patients that smoked, or consumed alcohol - for example, one population-based case-control study involving 204 patients and 415 controls reported that drinking green tea reduced the risk of liver cancer by 78% among alcoholic drinkers and by 43% among smokers.
Most of the research has centered around the green tea's catechins known as EGCG. In the studies, it was found to have chemopreventative activity in promoting cell death of cancer cells (apoptosis), restricting blood supply to the tumor, and inhibiting enzymes associated with some forms of cancer.
Research is ongoing, but nearly all of the studies showed some benefit, even in patients with other high-risk behaviors, like smoking. It makes sense to add green tea to your daily ritual for that extra bit of cancer-fighting power.
To learn more about the studies mentioned above, information can be found at Make a Habit of Green Tea Drinking for Prevention of Cancer