Tea and Heart Health
The strongest evidence is on the side of heart health, attributed to the antioxidant effects in tea. Studies that looked at the relationship of black tea intake and heart health reported decreased incidence of heart attack, whereas drinking green tea was associated with lower total cholesterol, LDL and triglycerides, and higher HDL (the "good" cholesterol) levels.
Tea and Weight Loss
Evidence supporting tea as a weight-loss aid is based mainly on studies that used tea extracts (epigallocatechin gallate and other polyphenols and caffeine). These results may not be directly applicable to brewed tea consumed in normal amounts.
Can Tea Prevent Cancer?
Support for tea's cancer prevention benefits is less compelling. It has been suggested that polyphenol compounds — particularly catechins — in tea may play a role in preventing cancer. However, studies related to black tea and different types of cancers have been extremely limited or conflicting.
Tea for Teeth
In 2010, Japanese researchers reported at least one cup of green tea per day was associated with significantly decreased odds for tooth loss. Other studies have suggested tea may lower the pH of the tooth surface, suppressing the growth of periodontal bacteria. A more likely reason for tea's anticariogenic effect is its fluoride content. Tea usually is brewed with fluoridated water and the tea plant naturally accumulates fluoride from the soil.