Both green and black teas contain a concentrated dose of catechins, substances that help blood vessels relax and protect your heart. In a study of more than 40,500 Japanese men and women, those who drank 5 or more cups of green tea every day had the lowest risk of dying from heart disease and stroke. Other studies involving black tea showed similar results. You really need only 1 or 2 cups of tea daily to start doing your heart some good—just make sure it's a fresh brew. Ready-to-drink teas (the kind you find in the supermarket beverage section) don't offer the same health benefits. "Once water is added to tea leaves, their catechins degrade within a few days," says Jeffrey Blumberg, PhD, a professor of nutrition science and policy at Tufts University. Also, some studies show that adding milk may eliminate tea's protective effects on the cardiovascular system, so stick to just lemon or honey.