The bulk of the research on tea till now has focused on the antioxidants it contains, the flavonols, catechins, and lignans that appear to arm the body against disease. It's thought that they improve blood vessel dilation, for example, and lower the risk of aortic atherosclerosis. "We know that the more tea one consumes, the stronger the cardiovascular protection will be," says Lenore Arab, a nutritional epidemiologist at the University of California-Los Angeles David Geffen School of Medicine. By inhibiting damage to dna, some researchers theorize, the antioxidants may also slow tumor growth.

Now neuroscientists are weighing in with evidence that components in the leaves of the Camellia sinensis plant may work wonders in the brain as well. According to Foxe's research, the amino acid theanine, which is found in green, black, and oolong teas, causes a decrease in the brain's "alpha rhythms" when people perform complex attention tasks, causing them to pay closer attention. His ongoing research, funded by the food and beverage conglomerate Unilever, suggests that theanine and caffeine together improve performance more than either substance alone. The findings, described in September at a conference on tea and human health, argue for further studies specific to add, Foxe thinks.

Other brain studies are still in the very early stages but offer hope that tea might battle degenerative diseases like Parkinson's and Alzheimer's, too. Silvia Mandel, vice director of the Eve Topf and the National Parkinson Foundation Centers in Israel, has found that—in mice, at least—tea's main antioxidant shows an ability to curb brain cell death and encourage neurons to repair themselves.