The scientific study of green tea’s cancer-preventive properties began about 20 years ago. Today, green tea extracts and catechins are globally recognized as important functional food components with potential cancer-preventive effects, driving ongoing vigorous research.

To be scientifically validated, the effectiveness of green tea in cancer prevention must clear three hurdles: epidemiological data showing a correlation between green tea consumption and reduced cancer incidence or mortality, experimental data supporting these findings, and finally, confirmation of efficacy through human intervention or clinical trials. Current research is deeply engaged in the third phase.

Epidemiological Studies:
Reports from Shizuoka Prefecture (Oguni et al., Shizuoka University) and the Kitakyushu region (Furuno) indicate a correlation between green tea consumption frequency and reduced gastric cancer mortality rates. The U.S. National Cancer Institute (1994) also confirmed a link between habitual green tea drinking and reduced esophageal cancer incidence in a study conducted in Shanghai, China. However, there is insufficient evidence to conclusively prove that tea consumption universally prevents various cancers. For black tea, there is virtually no data suggesting a correlation with cancer prevention.

Experimental Studies:
Extensive data from animal studies and in vitro experiments support the anti-carcinogenic effects of green tea extracts and catechins. Some animal studies, however, show inconsistent dose-response relationships, with higher inhibitory effects at lower doses. Research by Nagoya City University on multi-organ mid-stage carcinogenesis models revealed that the effectiveness of green tea catechins is not uniform, highlighting existing challenges.

Mechanisms of Cancer Prevention:
Green tea catechins have shown effectiveness in several key areas:

1. Inhibition of mutations (initiation of carcinogenesis)
2. Inhibition of cancer promotion (promotion stage)
3. Inhibition of malignant transformation (progression stage)
4. Specific inhibition of cancer cell proliferation (selective cell growth inhibition and induction of apoptosis)
5. Inhibition of cancer cell metastasis

No other food component exhibits such multifaceted inhibitory effects, and research continues at the molecular and genetic levels.

Absorption and Metabolism:
Data on the absorption, metabolism, and excretion of green tea catechins in animals and humans are still insufficient. It is estimated that a few percent are absorbed, with most excreted in feces, necessitating further analysis.

Daily Intake and Effective Dosage:
For individuals consuming 10 cups of sencha daily, the intake of green tea catechins ranges from 0.6 to 1.2 grams per person per day, with lower amounts from bancha and canned drinks containing about half to two-thirds the catechin levels of loose leaf tea. Effective cancer-preventive dosages are suggested to be 20 mg/kg body weight/day from epidemiological data and 10 mg/kg body weight/day from animal studies, with clinical applications using 20 mg/kg body weight/day. For a Japanese individual weighing 50-60 kg, this translates to 1.0-1.2 grams per day, roughly equivalent to three large cups of powdered tea served at sushi restaurants.

Human Intervention Trials:
A cohort study by Nakachi et al. at the Saitama Cancer Center reported delayed cancer onset in patients drinking over 10 cups of tea daily and improved prognosis with lower recurrence rates in breast cancer patients drinking over 5 cups daily. Clinical trials for green tea catechins and extracts as cancer preventive agents have been underway in the U.S. since September 1997, involving collaborations between Japanese corporate research institutes, the U.S. National Cancer Institute, and the University of Texas MD Anderson Cancer Center. Reports from summer 2000 indicate that these trials have entered Phase II.

In the near future, green tea and catechins may be incorporated into dietary menus for general cancer prevention and used as preventive medicine for high-risk groups.