This is an interesting one.
The largest trial to date came from Japan. In the Ohsaki Studay, published in JAMA in 2006, investigators enrolled 40, 000 patients. After 11 years, "Green tea consumption was inversely associated with mortality due to all causes and due to cardiovascular disease." Interestingly, "the inverse association with all-cause mortality was stronger in women."
While still speculative, the possible mechanisms include green tea's antioxidant properties as well as its ability to help cholesterol and high blood pressure.
Therefore, while not definitive, there is definitely no downside to drinking green tea. There is the possibility that it might have a benefit, especially in women.