In addition, polyphenols inhibit enzyme activity that potentiates the malignancy of carcinogenic compounds. The link between tea and the prevention of heart disease is not yet as strong as that for cancer. It may be that tea polyphenols reduce blood cholesterol and reduce blood pressure. It may also prevent the formation of clots that can lead to heart attack or stroke. Both regular and decaffeinated tea, as well as ice tea, have comparable levels of polyphenols.
Tea is relatively low in caffeine, with the actual amount varying by brewing time and tea type.
Pound for pound, tea contains more caffeine than coffee, but because so much less tea is used to brew a cup, the caffeine content is much lower. A cup of black tea steeped for four minutes has 40 to 100 milligrams of caffeine, whereas a three minute infusion only contains about 20 to 40 milligrams. A comparable cup of coffee contains 60 to 180 milligrams. Oolongs have even less caffeine and green teas have negligible amounts. On the other hand, over the years, multiple attempts have been made to associate coffee with negative health effects.