All varieties of tea come from the Camellia sinensis plant. The most common varieties are green, white, black and oolong. Herbal tea and rooibos are not real teas, since they do not come from the plant.
Studies have been done showing that people who drink tea have lower occurrences of atherosclerosis, heart disease, and digestive system cancers. The protective benefit of teas is due to polyphenols, especially catechins, which are antioxidants that fight free radicals. A great deal of research has been done on green tea, which contains a high concentration of polyphenol called epigallocatechin-3-gallate (EGCG).
The decaffeinated varieties of teas have the same health benefits as the caffeinated ones. Cold tea has the same benefits as hot tea, as long as the tea was brewed in hot water with tea leaves and then chilled.
Source: Women’s Nutrition Connection