Green, black, and oolong teas -- along with coffee, red grapes, kidney beans, raisins, prunes, and red wine -- contain large quantities of polyphenols. Polyphenols, which are a class of bioflavinoids, have been shown to have antioxidant, anticancer, antibacterial, and antiviral properties.
Most of the polyphenols in green tea are catechins. Catechins, which are antioxidants by nature, have also been shown to function as anti-inflammatory and anticancer agents. One of the major catechins in green tea has been shown to be the most effective agent against skin inflammation and cancerous changes in the skin.
In their review of the scientific literature, Mukhtar and his colleagues found evidence that the compounds in green tea protected mouse skin from cancer caused by sunlight. Additionally, his team conducted a few experimental studies on human skin, and found that the polyphenols in green tea also had anti-inflammatory and anticancer properties.
While acknowledging that antioxidants are important, Allan Conney, PhD, believes there may be more at work. Conney's lab is also trying to unravel the mechanism by which green tea protects against cancer, and is now looking at the effects of the caffeine. "In our studies, if we remove the caffeine from tea and feed the decaffeinated tea to mice at a moderate dose, it loses most of its effectiveness at inhibiting ... skin cancer," says Conney, director of the Laboratory for Cancer Research at Rutgers University College of Pharmacy in New Jersey.
"The important question is, what happens in people?" says Conney. "There is a need for more clinical studies in the future in order to be able to say tea has a beneficial effect in preventing ... human sunlight-induced skin cancer."