Yes and no. The truth is that tannins are neither bad nor good for you. When taken in moderate amounts, tannins can help the human body to stay in good health. These can even help prevent certain diseases. It is because tannins are some kind of antioxidants as these are the oxidized cathecins often found in tea. On the other hand, too much tannins may also disrupt the health of a person and anemia is among the side effects cited often. Just like anything, tannins must only be taken in complete moderation.