Tea is a name given to a lot of brews, but purists consider only green tea, black tea, white tea, oolong tea, and pu-erh tea the real thing. They are all derived from the Camellia sinensis plant, a shrub native to China and India, and contain unique antioxidants called flavonoids. The most potent of these, known as ECGC, may help against free radicals that can contribute to cancer, heart disease, and clogged arteries.
All these teas also have caffeine and theanine, which affect the brain and seem to heighten mental alertness.
The more processed the tea leaves, usually the less polyphenol content. Polyphenols include flavonoids. Oolong and black teas are oxidized or fermented, so they have lower concentrations of polyphenols than green tea; but their antioxidizing power is still high.