In a study by Y. Kuroda, and Y. Hara in Mutation Research 436 (1999), the authors state that the "polyphenols in tea have a strong radical scavenging and reducing activity...that capture and detoxify radicals of various promotors of carcinogensis and radicals produced in the process of exposure to radiation and light." Tea polyphenols inactivate enzyme and virus activity and thus, may modulate the efficacy of viruses in producing cancerous by-products. Cathechins are in a far higher concentration in green teas and less oxidized teas such as Wu Long than in Black teas.
The Japanese Cancer Association as well as the Ministry of Health and Welfare reported that death rate from cancer in both females and males in Shizuoka Prefecture was much lower than the mean for all of Japan. In addition, greater intake of a partially fermented tea, such as Wu Long tea was correlated with a lower risk of lung cancer in women. As little as 1-4 metric cups a day led to significant results, though the best results were obtained from women who drank 10 cups or more. Similar results were found for men.
In female rats, Weisburger et al. reported that the volume of mammary tumors in female rates was decreased by 1.25% when the rats drank 2% tea beginning 1 week before carcinogen administration. The authors conclude by highlighting the effects of tea in the suppression of a rise in blood pressure and the reduction of blood glucose. Tea polyphenos also have an antibacterial effect against food borne bacterial was well as dental caries caused by bacteria.