Really not sure if Green Tea Extract would have this effect, but green tea (much like other tea's) has many health benefits due to the antioxidants it contains.
I drink 2 cups every day, green tea can be an acquired taste, if you buy the cheap brands like Clipper they can taste like dish water, we get our tea from Holland & Barrett and the brand name is Double Dragon, it's a excellent quality tea but is a little pricey at nearly £2 for a box of 20.
H&B also do their own green tea which contains lemongrass, that is nice too for those who want a sweeter taste.