Polyphenols are most definitely antioxidants, which means that they can reduce the risk of developing coronary artery disease and a number of other health problems. The polyphenols found in tea have also been linked with cancer reduction, as they appear to block the action of some enzymes linked with cancer. Because cancer is so complex and it can be influenced by many environmental and genetic factors, scientists are reluctant to say that tea polyphenols will categorically prevent cancer, although cancer rates do seem to be lower in tea drinkers after controls for other obvious factors like diet are used to evaluate the data.

The polyphenols found in tea also appear to suppress the growth of harmful bacteria, while promoting beneficial bacteria in the gut. The Chinese tradition of drinking tea with and after many meals may be linked to this activity, as food can be a prime source of bacterial infection when it is not handled well, and drinking tea with food could reduce the risk of developing infections.

The flavor of tea is also influenced by tea polyphenols. Tannins, found in high concentrations in black tea and lower concentrations in green and white tea, lend tea its distinctive dark color and bitter, sharp flavor. Other polyphenols can also change the color of the tea, making it more reddish or brown depending on how it is handled, and the subtle and distinctive flavors of well-processed teas are due in part to polyphenols.