Drinking three or more cups of black tea a day protects against heart disease and two or more cups a day may protect against type 2 diabetes, a review in the journal Nutrition Bulletin found.
According to experts, the benefits of tea are largely due to the flavonoid content - antioxidant ingredients that counteract cardiovascular disease.
One cup of tea provides 150-200mg of flavonoids and it is the best source of antioxidants in the diet.
Nutritionist Carrie Ruxton, co-author of the latest review and a member of the industry-backed Tea Advisory Panel (TAP), said: "There is far more to the nation's favorite drink than we realise.
"With its antioxidant flavonoids, black tea packs a powerful punch with many health benefits particularly for the heart. And recent studies show that the flavonoids work their magic whether or not we choose to add milk."
In addition, a 12-week study of 87 volunteers showed how drinking three cups of tea a day produced a significant improvement in various cardiovascular risk factors.
Flavonoids found in tea are thought to control inflammation, reduce excess blood clotting, promote blood vessel function and limit furring up of the arteries.