Coffee, Dehydration and Tannin

Caffeine acts as a diuretic, which means that it dehydrates your body. Two or three cups of coffee per day would not dehydrate your body too much. However, if  you drink six or more cups of strong coffee per day, it may not be good for you. 

Coffee contains chemical compound called tannin. Tannin is a natural organic substance (polyphenols) which can be found not only in coffee or tea but also in wine, berries, nuts, and some herbal teas. Research results show that tannin affects iron absorption.

If you drink a lot of coffee every day, you should probably eat more food that contains iron, e.g. nuts, beef, green vegetables and  beans.

Tannin dehydrates your skin and has some other side effects