Tea comes from the leaves of the warm-weather evergreen Camellia sinensis, and it is classified into five types: black, white, green, oolong and puerh.
Experts say all are healthful. Many scientists link health benefits to tea's polyphenol antioxidants, which protect against oxidative stress, but others say they don't know exactly which chemicals or combinations of chemicals in tea produce the benefits. Sherman, for example, said there's no evidence connecting tea's antioxidants to beneficial effects, and he pointed to a study showing that black tea reduces LDL, or "bad," cholesterol without affecting antioxidant levels, suggesting something else in tea is causing this.
Numerous epidemiological studies — which establish correlation, not cause and effect — focus on tea's role in reducing cardiovascular disease, the nation's biggest killer.
A 2004 paper in the Archives of Internal Medicine, for instance, looked at hypertension rates among people who drank tea for at least a year. The study, conducted in Taiwan, found that those who drank about four ounces to 20 ounces of tea a day had a 46 percent lower risk of developing high blood pressure than people who didn't drink tea regularly.
Another paper, published in 2002 in the American Journal of Clinical Nutrition, culled through the results of a large study concerning chronic disease and found that people drinking the greatest amount of tea — more than 12 ounces a day — had barely half the risk of heart attack as people who did not drink tea.
More recent cardiovascular research was presented in September at a symposium at the Department of Agriculture in Washington. One study found that black tea reduced blood pressure in all participants and counteracted the detrimental effects of high-fat meals in people with high blood pressure.
"The more tea you drink, the better," Sherman said. "It's astounding, really."