For approximately 20 years, academic exploration into the cancer prevention potential of green tea has been ongoing. Green tea extracts and catechins are now globally recognized as some of the most significant functional food components for potential cancer prevention, attracting vigorous research attention.
Validation of Effectiveness The effectiveness of green tea in cancer prevention is validated through three major hurdles:
- Epidemiological data showing correlations between green tea consumption and reduced cancer incidence or mortality.
- Experimental data supporting these findings.
- Human intervention trials or clinical trials confirming efficacy, which are currently underway.
Epidemiological Studies Reports from Shizuoka University and North Kitakyushu have shown correlations between green tea consumption frequency and lower stomach cancer mortality rates. The U.S. National Cancer Institute confirmed a correlation between habitual green tea consumption and suppressed esophageal cancer development in Shanghai, China. However, comprehensive evidence supporting tea consumption for the prevention of cancer in other organs is still insufficient.
Experimental Data A vast amount of data from animal and in vitro studies supports the anti-carcinogenic properties of green tea extracts and catechins. However, issues remain, such as inconsistent dose-response relationships, where lower doses sometimes show stronger inhibitory effects.
Mechanisms of Action Green tea catechins inhibit multiple stages of carcinogenesis:
- Suppression of mutations (initiation).
- Inhibition of cancer promotion.
- Suppression of malignancy progression.
- Selective inhibition of cancer cell proliferation and induction of apoptosis.
- Inhibition of cancer metastasis. These diverse inhibitory actions are not commonly found in other food components, and research continues to elucidate their molecular and genetic mechanisms.
Absorption, Metabolism, and Excretion The absorption, metabolism, and excretion of green tea catechins in animals and humans are not yet fully understood. Studies suggest only a small percentage is absorbed, with the majority excreted in feces.
Consumption and Dosage A daily intake of about 0.6 to 1.2 grams of green tea catechins is typical for someone who drinks about ten cups of sencha. The effective dose for cancer prevention has been estimated at 20 mg/kg body weight per day based on epidemiological data, with clinical applications using the same dosage.
Human Intervention Trials Research by Saitama Cancer Center researchers has shown that consuming more than ten cups of tea per day can delay cancer onset, and more than five cups per day can reduce recurrence rates in breast cancer patients. Clinical trials of green tea catechins and extracts as cancer preventive agents began in the U.S. in 1997, in collaboration with Japanese research institutions and the U.S. National Cancer Institute.
Future Prospects Green tea and its catechins might soon be incorporated into cancer prevention diets for healthy individuals and potentially as preventive medication for high-risk groups.