Preliminary evidence suggests that tea may reduce risk for cardiovascular diseases, cancer, and dental caries and increase risk of certain nutritional deficiencies. All tea is not alike. Green tea is dried fresh tea leaves. Green tea is commonly consumed in Asian countries.
Black tea is made of tea leaves that are crushed, allowing enzymes to catalyze oxidation.
Black tea is usually consumed in Western nations. A third type of tea, oolong, is made from tea leaves that are partially fermented. Some research has not differentiated between the types of tea and is, therefore, inconsistent and difficult to interpret. Tea catechins have attracted the most interest because they are capable of antioxidant activity. Catechins are absorbed and appear in the circulation within 1-2 hours after ingestion.