studies done on rodents with extremely high levels of green tea extract found this to be the case. BUT you'd have to drink swimming pools of the stuff to come anywhere close to the levels of green tea extract in the trials.
The other thing is: you are not a rodent.
unless of course you are. which I doubt.
so, if you drink a few cups of green tea, even brewed strong, per day ... you'll be getting benefits but seriously you are not going to get that sort of side effect..