As for cancer prevention, the evidence is less compelling.
A review of studies published in the Journal of Cancer Research and Clinical Oncology last year suggested that consuming 10 Japanese-size cups of green tea a day helps prevent several cancers and protect against recurrence of colorectal cancer. And a 2006 review in the Journal of the American College of Nutrition of the beneficial effects of green tea noted studies linking tea to reduced risk of ovarian, prostate and breast cancers.
But that review also cited some conflicting research. For example, two studies revealed a breast cancer benefit, one showing a decreasing risk among Asian American women with rising tea intake and another showing a lower risk of recurrence among Japanese patients who drank three or more cups a day. But a larger Japanese study of more than 35,000 women concluded tea intake didn't affect the risk of breast cancer.
And scientists at the Johns Hopkins Kimmel Cancer Center announced last week that black and green teas (and coffee) were among the foods and flavorings that affected a gene linked to cancer. But they said this doesn't mean people should stop drinking tea and coffee, only that more research is needed.
Studies have also examined whether tea affects weight loss. One, from 2004, found that caffeine, theanine and perhaps other components in green tea powder suppressed weight gain and fat accumulation in laboratory mice.
There is also some evidence that drinking tea promotes digestive health generally. Gerry Mullin, an associate professor of medicine at Johns Hopkins School of Medicine and author of "The Inside Tract: Your Good Gut Guide to Great Digestive Health," said tea appears to help control glucose and insulin and keep the gastrointestinal system running well.
"At the end of the day, these teas are anti-inflammatory in nature. They have anti-bacterial properties," Mullin said. "They [boost] the immune system and provide a lot of different benefits."