Becky--the study they are talking about is probably the one done in Germany a few years ago. Again, it was a "small" study. I am not aware of anything else out there.
I have heard that drinking large amounts of tea can decrease your iron levels though. I had a friend who was an iced tea addict in the summer and was with him at a Red Cross blood drive and his iron was too low. The first thing they asked was how much tea he had been drinking. (He drank a LOT!) They told him to lay off it a couple days and then come back. So I don't think it lowers it for long. But again--I only know this from the Red Cross people telling him that not any study.