Like black and green teas, oolong contains an abundant source of natural plant-derived antioxidant compounds called polyphenols. Included within the broad antioxidant polyphenol class are flavonoids and catechins. A kind of flavonoid, catechins are found in tea leaves and may provide protective antioxidant action against harmful free radicals. Research shows that these free radicals cause heart disease, some kinds of cancer and increase the risk of strokes. Drinking oolong tea with its high antioxidant levels help protect the body by combating dangerous free radical activity. In addition, oolong tea provides a source of nutrients including magnesium, Manganese, potassium, calcium, the vitamins C and K and the amino acid theanine, all in trace amounts.