The way scientific studies and health gurus alike have touted the perks of tea over the past few years, you'd think the stuff was some kind of all-powerful magical elixir.Improving heart health, reducing cancer risk, warding off dementia and diabetes—there's barely a health benefit that hasn't been credited to tea.It's true that the brew has disease-fighting antioxidants, and, as far as anyone can tell, should be great for us. "The science is certainly promising," says David L. Katz, MD, director of Yale University's Prevention Research Center. "But the hype goes beyond it and tends to make promises which the science can't yet deliver." (No, tea probably will not cure depression, eliminate allergies, or boost your fertility!) We talked to the experts and weighed the studies to separate the truth from the hype.Why tea is so hotFirst, a definition: When scientists talk about tea, they mean black, green, white, or oolong teas—all of which are made from the leaves of the Camellia sinensis plant. Herbal brews, like chamomile and peppermint, are not technically considered tea; they're infusions of other plants with different nutritional characteristics. If you're not sure what kind you're drinking, check the ingredients for the word "tea."What makes the four tea types different from each other is the way the leaves are prepared and how mature they are, which affects both flavor and nutritional content. Black tea is made from leaves that have been wilted (dried out) and then fully oxidized (meaning that chemicals in the leaves are modified through exposure to air). Green tea's leaves are wilted but not oxidized. Oolong tea is wilted and then only partially oxidized, and white tea is not wilted or oxidized at all.All four types are high in polyphenols, a type of antioxidant that seems to protect cells from the DNA damage that can cause cancer and other diseases. It's the polyphenols that have made tea the star of so many studies, as researchers try to figure out whether all that chemical potential translates into real disease-fighting punch. Most research has focused on black tea, which is what about 75% of the world drinks, and green tea, the most commonly consumed variety in China and Japan.Green tea contains an especially high amount of antioxidants—in particular, a type of polyphenol called a catechin, the most active and abundant of which is epigallocatechin-3-gallate (EGCG). That's why there are five times more studies on green than black tea each year—and likely why you're always hearing about the power of the green stuff, says Diane L. McKay, PhD, assistant professor of nutrition at the Tufts University Friedman School of Nutrition Science and Policy.