Tea polyphenols are natural phenol compounds found in several varieties of tea that are also referred to commonly as flavonoids. One of the reasons that these compounds are often mentioned as being so beneficial as tea polyphenols is that they are highly concentrated in tea products. The major category among flavonoids found in tea are known as catechins, and green tea has a higher concentration of them than any other type of tea. Flavonoids serve as antioxidants and protect the body from free radical damage, which can lead to cancer, and are concentrated at ten times the level in green tea polyphenols and black tea polyphenols as compared to antioxidant levels found in fruits and vegetables.
While different styles of tea taste different and are processed differently, some of them come from the same source and therefore have similar concentration of tea polyphenols. This is true of green tea, black tea, and oolong tea that are all derived from the Camellia sinensis species. Both black and oolong teas are fermented, while green tea leaves are steamed, which leads to the differing flavors. The main beneficial antioxidants in these three types of teas overall are the catechins, epicatechins, and thearubigins. Other types of tea polyphenols also exist in different tea flavors including herbal teas, but medical research on the benefits of these other varieties has not been as extensive as of 2011.
Aside from serving a role to protect cells from damage caused by free radical oxygen molecules in the bloodstream, tea polyphenols have been shown to have other health benefits as well. These include preventing damage to DNA caused by cigarette smoke or through other uses of tobacco, and also blocking the harmful effects of other toxic chemicals that enter the bloodstream. Incidences of heart disease are statistically reduced in nations like China and Japan versus occurrence levels in western nations. Traditions of consuming large amounts of green and black tea in these nations has led to the conclusion that reduced heart ailments are in part attributable to tea polyphenols. Population studies have also shown reduced rates of diabetes in nations where high tea consumption is the norm.
Other tea polyphenols are also found in many natural teas such as kaempferol and quercetin, but the concentrations are lower and extensive research has not been done on their benefits. A 2006 study of residents of Japan and Taiwan also found that drinking a cup of green or oolong tea with a high-fat diet significantly reduced bad cholesterol levels. Evidence further suggested that regular consumption of these teas could lead to weight loss and could also delay the onset of Alzheimer's disease.